March 1975 Bulletin 467 11a~te r I'otton: A Rh izotro ii S1udv! AGRICULTURAL EXPERIMENT STATION AUBURN UNIVERSITY R. Dennis Rouse, Director Auburn, Alabama CONTENTS Page INTERPRETIVE SUMMARY 3 LIST OF TABLES AND FIGURES INTRODUCTION MATERIALS AND METHODS 4 5 6 Construction Details of the Rhizotron Soil Preparation and Measurement Measurements of Root Parameters Plant Shoot Measurements Time Course of the Experiment RESULTS AND DISCUSSION .......- 6 9 10 11 14 15 Compaction Treatment, Bin 2 15-cm Treatment, Bin 4 155-cm Treatment, Bin 5 55-cm Treatment, Bin 6 Drying Control, Bin 7 Well-water Control, Bin 8 CONCLUSIONS 15 15 17 17 22 23 30 LITERATURE CITED 32 APPENDIX I 8833 33 Monitoring Environmental Conditions: Data Acquisition, Reduction, and Storage APPENDIX II 40 -Data Not Cited in Text and U.S. Weather Bureau Data -- 40 66 66 APPENDIX III Publications for which Research was Conducted Wholly or Partially in the Auburn Rhizotron FInRsT PRINTING 2M, MARCH 1975 Auburn University is an equal opportunity employer. INTERPRETIVE SUMMARY Long-term drought probability data collected for Alabama and other southeastern states have shown that despite the high annual rainfall, cotton plants will suffer at least 20 days of seasonal drought in 9 out of 10 years. While the number of drought days can be reduced by encouraging deeper root penetration, these practices are generally expensive. The experiments reported in this bulletin are designed to permit quantitative estimates of the economic return from practices which increase the effective soil water storage capacity. The response of cotton plants to water stress was carefully monitored, and the precise time and amount of water stress was estimated by specially developed instrumentation in the Auburn rhizotron. Beyond the general conclusion that deeper roots are as effective as shallow roots in supplying the needs of cotton plants, a number of specific hypotheses relating to the mechanisms by which plants remove water from the soil was tested. These conclusions are reported elsewhere in technical journals. This bulletin includes extensive summaries of the data obtained for those wishing to test their own hypotheses against the data obtained in this set of experiments. LIST OF TABLES AND FIGURES Table 1. Total root length and root length in soil wetter than -1 bar for all bins containing cotton at the Auburn rhizotron, 1972. Table 2. Leaves and bolls present on September 5 for the various cotton plants in the experiment. Table 3. Summary of plant top measurements made during the 1972 growing season for cotton plants of bin 5, Auburn rhizotron. Table 4. Volumetric water content as function of depth and time in bin 5, Auburn rhizotron, 1972. Table 5. Rooting density as a function of depth and time in bin 5, Auburn rhizotron, 1972. Table 6. Summary of plant top measurements made during the 1972 growing season for cotton plants in bin 6, Auburn rhizotron. Table 7. Volumetric water content as funetion of depth and time, and total water-use as a function of time for bin 6, Auburn rhizotron, 1972. Table 8. Rooting density of cotton as function of depth and time in bin 6, Auburn rhizotron, 1972. Figure 1. Aboveground view of the Auburn rhizotron. Figure 2. Underground view of the Auburn rhizotron showing the glass fronts of compartments on each side of the central walkway. Figure 3. Glass face of a compartment of the Auburn rhizotron showing the wire grid used as a reference for root measurements. Figure 4. LVDT apparatus used for continuous monitoring of stem diameter. Figure 5. Diagram showing how data were obtained on stem shrinkage and swelling for reporting in tables. Letter "A" designates the maximum stem diameter attained during the night: "B" the minimum diameter obtained during the day; "C" the point on the curve when the stem diameter returned to its early morning maximum value; "D" the point where the night curve begins to appear linear; and "A1 " the maximum stem diameter attained during the following night. In the tabulated data, the third column is the time, "D"; the fourth column is the diameter at "Al" minus the diameter at "'A"; the fifth column is the length of time represented by the length of line "AC"; the sixth column is the distance in mm at which point "B" is below line "AC"; and the seventh column is area "ABCA." WATER RELATIONS of COTTON: A RI-IIZOTRON STUDY' V. DOUGLAS BROWNING, HOWARD M. TAYLOR, MORRIS G. HUCK, and BETTY KLEPPER 2 INTRODUCTION PLANT GROWTH requires a steady supply of water, the ability of a root system to continue supplying water during a drought can mean the difference between success and failure of a crop. Alabama receives about 125 to 150 cm (50 to 60 inches) of moisture annually, often as widely-spaced afternoon thundershowers during the growing season. Consequently, droughts occur periodically, and those plants with deep, well-proliferated root systems survive better than those with shallow, sparse roots. Previous experiments, Pearson (11) showed that soil layers restrict roots whenever soil pH is below about 4.5 to 4.8, soil bulk density of a loamy fine sand is above 1.80g/cm8 , and that of silt loam is above 1.65 g/cm3 . Many soil managementpracticesencourage root extension deeper into the soil. For example, a compacted soil can be loosened by various mechanical treatments; an acid soil can be limed. However, these are expensive operations, and more information is needed to determine the relative effectiveness of roots at different depths in the soil and to evaluate the effectiveness of root systems in supplying sufficient water and SINCE 'Contribution from Soil and Water Research, Southern Region, Agricultural Research Service, U.S. Department of Agriculture, in cooperation with the Departments of Agricultural Engineering, Agronomy and Soils, and Botany and Microbiology, Auburn University, Auburn, Alabama. 2 Respectively: Agricultural Engineer, Southern Region, ARS, USDA cooperative with the Department of Agricultural Engineering, Alabama Agricultural Experiment Station, Auburn University; Soil Scientist, North Central Region, ARS, USDA, Ames, Iowa, formerly of Auburn, Alabama; Soil Scientist, Southern Region, ARS, USDA, cooperative with the Department of Agronomy and Soils, Alabama Agricultural Experiment Station, Auburn University; and Research Scientist, Ecosystems Department, Battelle Northwest Laboratories, Richland, Washington, formerly Assistant Professor, Department of Botany and Microbiology, Alabama Agricultural Experiment Station, Auburn University. 6 A L A A LAAA AGRICULTUR~AL EXPERIMENT STATION Adamis et al. (2) found that xxbeu su rfacc soil xxas Mjilied and fe;tiliicd, a~ttoii hci ht in creased fastcr dnIiviii jumi aid (1iix xxho'i the subhsoil plh was iuodcratelx acid thain xxhen subsoil ph1 xxas 1)c.hmx .. Thic AuburnI rhlizo(tron. Tado (1i wxas lImilt (lii ]4 1965' aind 1969 to stiitl factors underlc coniditionis simiilar to those (\ 1 itcd ini field. the TLhis report dlescrnihes an 2\~ viii ('I it ini the s1immicrte of 1972 coiidiicted in the rhizotioni to Stni(\ (I ) the influii'ice o1 rootiii(r dIepthl aid 1((eiisitx upon1 i rv th and itixater uptake pattern s of cottoii puits, 2 the iiifaueiiec of plaiit wxater siipply on «roxx tb ? ate and yIxield. (3 ) the iitilitx of xariotis plant xxatei su ppIN pava ictevs in pr edictii t reduce( roxx th rate due to wxater stress. andc to dlocueniiit ( 4 ) the situiltaiieoiis reactioiis of1 cottoii tops aiid root sx stemos, Broiixxer and( dc\\ it (4) toi plaint xxater stress. MATERIALS AND METHODS Construction Details of the Rhiizotron 11li \iilbiiii rhizo(tron i Leure 1, is an ii uuIl-groiun d root obscrxatioii labotratorx x it I t)10 )artiiicits on each sice iiiia cell- FIG. 1. Aboveground view of the Auburn rhizotron. WATER RELATIONS of COTTON 7 2. The cenotral endr(1( 2rollndc xxalkxx ax is to prop idle a tempileratuire near the meani of the( soil tcrpeatije pro~he in) adhiac int fied soil. Vatch co)mpartmien t hias a glass side facii!. the wxalkwxax. side panels oif steel or ahiin t plate 1 tt xx n tei stajin1(ss steel sheets, a rear w\all xx i h is tho OIf er ietainer( coincrete xxaH. and a hiottcIl ci oisisting or(f It) co f-inchl ) tiricl: conert shalb. Con1crtete sillf aces hax e b)e (1 treated wxith epo\\' painut to redu lce soil conitam in ation bx the concrete imaterijal. All joinits and c acks liaxve 1 t i scaledi xxith si licone eaiilkiui sealan t. Each comlpartmlenlt is al toit I S8 cmi 4 iliehes ) hi~ri 12 (" m (418 inchles ) xxidc, and 60 cm ( 24 iniches) f1r1m front to rear. xxith atotal xolille o)1 1.3 1113 47.8 It." ). Four reeta1Mi ular porous plates. 15 I 15 1.3 cimi I6(x 6 I inch ) xxitli drain age tuoes F'igure air-coniditioi 11d tral xxalkxxa a, t- -~ FIG. 2. Undergro3und visw of the Auburn rhizjfron- -howirg the glass fronts of compartments on each side of the central walkway. 8 ALABAMA AGRICULTURAL EXPERIMENT STATION xxere placedl in the bottom of each com partmnlt and covecred with a 5-cm (2-inch ) lax er of dliatomaceous earth. The vertical glass tront of each c)mpartmeiit consists of :32 glass panes albout 25 cm ( 10 inches) s( uare and 0.6 cm (1,4 inch ) thick, %vith1.2.5-cnm l inch ) sq uare (grid wire mIesl embiiledded ini thet Mlass, Figrure 3. This wxire prox ides a stab~le reference grid for root measurenments and also reduces shattering if the glass breaks. Vertical stainless steel b~ars, 1.3 x .5.0 cm (I x 2 inches) support the glass panes that are attached 1w stainless steel clips andl sealed Wxith silicone caulking se'alant. 11v use of the rhizotron, then, repe'titiv e roeasurements of a growxing root sy stem ox er the entire life of a cotton ( Goss?,pium hirsuon ) plant can he made . A comparisoni of successic enasulrem~ents wxill showx growxth or rotting of a population of roots at a gix en1 d epth for each treatment ini ani experimnie t. Facilities for nmcroscopic ob serv ation s of roots groxxin g ini a parti culmar soil (lix iroimnent are av ailable, and time-lapse cinematography prox ides a p~ermanen1(1t reco rdl of certain selected experimlents. * FIG. 3. Glass face of a compartment of the Auburn rhizotron showing the wire grid used as a reference for root measurements. WATER RELATIONS of COTTON 9 Soil Preparation and Measurement Six of the 20 rhizotron compartments (bins) were used in this study. Three were filled with loamy fine sand, the Ap horizon of Cahaba soil from Tallassee, Alabama. They were designated as (1) control, well-watered (Bin 8); (2) control, allowed to dry (Bin 7); and (3) compaction treatment (Bin 2). The compaction treatment consisted of trampling the soil by foot after the compartment had been filled to within 15 cm (6 inches) of the top, and then filling in the top 15 cm with loose Cahaba soil. A layer of acid subsoil (pH 4.6) from the 15- to 22-cm layer of a Dothan (formerly Norfolk) loamy fine sand was placed in the bottom of each of the other three compartments. Then they were filled with Cahaba loamy fine sand to obtain the following treatments: (1) 15-cm treatment (173 cm of acid soil overlaid by 15 cm of Cahaba loamy fine sand, Bin 4); (2) 55-cm treatment (13 cm of acid soil overlain by 55 cm of Cahaba material, Bin 5); and (3) 155-cm treatment (33 cm of acid soil overlain by a 155-cm layer of Cahaba material, Bin 6). The Cahaba material in Bins 4, 5, 6, 7, and 8 had a bulk density of about 1.3 g/cm 3; the compacted layer in Bin 2 was about 1.5 g/cm3 from about 15 to 25 cm deep. The soils for the experiment were prepared during the early spring of 1972. They were fumigated with methyl bromide and sieved through a 0.6-cm mesh screen to remove old root material. After bins were uniformly filled with soil to the desired density, they were fertilized on April 28 with nitrogen (NH 4NO 3 ) at the rate of 30 g N/m 2 and potassium (KC1) at the rate of 20 g K/m 2 per bin - the equivalent of 200 lb./acre of KNO 3 (16 g KNO 3 per bin). An additional 15 g N/m 2 was applied to each bin on June 23. At a 4.6 pH, the Dothan soil material in Bins 4, 5, and 6 had an aluminum activity of 35 M in the soil solution,.Pearson et al. (12). The relationship between water content and hydraulic conductivity was determined for Cahaba soil by the one-step method of Doering (5). The relationship between water content and total water potential was determined in situ in a bin of Cahaba soil, using water content measured by a neutron absorption meter and total water potential measured by thermocouple psychrometer calibrated as described by Fiscus and Huck (6). A neutron meter access tube was installed in the center of each compartment and sealed at the bottom and top with a rubber 10 ALABAMA AGRICULTURAL EXPERIMENT STATION stopper which prevented water from seeping into the tube. The neutron probe was calibrated for Cahaba soil in a rhizotron compartment at the end of the growing season, with the access tube in the same position during calibration and measurement. Measurements of Root Parameters The quantity of root material at a particular depth on the glass face was assumed representative of the roots at that depth throughout the compartment. A previous experiment, Taylor et al. (15) and an unpublished one by F. M. Melhuish, B. Klepper and M. G. Huck, have shown little or no concentration of roots at the glass surface. Rooting density was defined as cm of root length in a cm 3 of soil volume. Rooting intensity was defined as cm of root length visible per cm2 of viewing surface. In this Cahaba soil it was estimated that one could see 0.2 mm into the soil and assumed that all roots in the 0.2-mm layer adjacent to the glass were visible and all roots further than 0.2 mm from the glass were not visible. Depth of vision into the soil was confirmed periodically by microscopy. On the basis of these inferences, rooting density was calculated from root intensity measurements simply by multiplying by 5. At 2-day intervals root intensity at 15-cm depth increments along the glass was estimated by the line-transect method, Taylor et al. (15), from the number of roots crossing a 105-cm transect. The relationship between root intensity and number of roots crossing the transect was obtained in early August when a range of values was available for measurement. The root count-root intensity relationship was established by the following technique: An operator counted the number of roots intersecting a 25-cm horizontal transect and obtained 56 data sets, and measured the length of roots appearing in an area within and 1.3 cm on either side of that transect line with a ruler. Statistical analysis was employed to obtain the regression formula between root length and number of root intersections: (1) I =- -0.00003316 N2 + 0.00485 where I is root intensity and N is the number of roots intersecting a given transect line across the face of a bin. The correlation coefficient was 0.98. This equation differed slightly from that previously developed for corn and tomato root systems, Taylor et al. (15), possibly because of a difference in the anisotropy term, Lang and Melhuish (10), between cotton and the other species. WATER RELATIONS of COTTON 11 Plant Shoot Measurements Plant water potential was determined three times weekly on detached leaves with a pressure chamber, Klepper and Ceccato (8), when measurements were made twice daily (0700 and 1400 hr.). Sampling on one of the two plants in each treatment was started on the hour followed by a second series of samples on the other plant in each treatment. Additional replication was impossible because of the limited number of plants in the study. The leaves on the plants in the 15-cm treatment (Bin 4) were insufficient for sampling more than a few times. Thus, generally 10 samples were taken at each sampling time. Since 3 to 5 min. were required to process each sample, the time of sampling was different for all treatments. This is important since clouds over a short period of time can have a marked effect on plant water potential, Stansell et al. (13). Therefore, the sampling order for the second series of treatments was reversed to make the average water potentials for the two plants as comparable as possible from one treatment to another. The early morning leaf samples were taken in the shade - usually on the west side of the plant to estimate the maximum plant water potential reached during the night. The afternoon leaves were also generally taken from the west side of the plant and were specifically chosen since they were exposed to the sun. Thus, they were chosen to reflect the minimum water potential values reached during the time of greatest stress. Two top growth measurements were made: plant height daily with a meter stick, and stem diameter (approximately 40 cm above ground level) continuously with a linear variable differential transformer (LVDT), as previously described, Klepper et al. (9). Each LVDT was incorporated into a holder which permitted recentering the LVDT core daily (Figure 4 showing LVDT arrangement) by turning the micrometer head, which provided an internal calibration standard in absolute units. Actual stem diameter was measured at installation with a micrometer caliper. Daily growth increments in millimeters were measured and recorded for later use in converting millivolt output from the LVDT's into diameter (millimeter) units. Since stem diameter decreases after dawn each morning, increases during late afternoon in response to reductions in evaporative demand, and generally continues to increase nightly, selecting a standard time to compare daily stem diameters for determination of daily growth ALABAMA AGRICULTURAL ALABAMA AGRICULTURAL EXPERIMENT EXPERIMENT STATION STATION V 4 FIG. 4. LVDT apparatus used far contirnuous monitoring af stem diameter. irineeit xwas arliitrarx . The authors eiiisc to comtpare the nmaximunl1 xvaltues jimediatelx beflore sontip, sinice c\ idieitly tiuse vaitics xxere less affected bx daiiix liidiffieces inl aerial ci ix iroi111(1 t. x ol tagcs fromli the I A VIs wxere recorded chart recordiers, at d( peni \oltagzcs of the reco)rdiers m oiiitored at 2-in l te iitcrx is in a digrital (lata acijusitioli sN stemo. \\ith data onl the iniitial x oltagre ai ( the initial stein di aileiter, tihe appropriate calillrat ion factors foir each cihanne], aiid the instanitaieou1s output signal x altu', a coiiipittr-dax I plot from magl(netic tape records ) oIf stem d Iiameiter in tniillieters for each pilnt wxas prepared throti ghotit tihe en tire cxpcritientii period. The 0o1tptit si gil al tolltiiiooi isix oil strip WATER RELATIONS of COTTON 13 Diameter of the central stem was monitored for both plants of all treatments except one plant in the 55-cm treatment which was not monitored because it could not be determined that a central stem existed. Because of occasional equipment failures, values are missing for some days on each treatment. When available, the continuous trace of stem diameter was analyzed to establish relationships among top growth and patterns of daily dehydration. Computer-drawn plots had the shape and appearance of the curve shown in Figure 5. For each plant of each treatment on each day, values were determined for (1) the time DA', i.e., the length of time nightly when the diameter appeared to increase linearly with time, (2) the time AC, i.e., the time length necessary for the stem to return to its early morning maximum diameter, or the duration of the shrinkage, (3) the distance below the line AC of point B, or the maximum amount of Stem diameter (mm) 9.440Al 9.280 D CI B 8.960 Aug. 17 8.800 8 1 Aug. 18 20 H u ( 0 4 Hours (0DT) 1 i 1 i i 16 20 ! I 24 12 16 8 12 FIG. 5. Diagram showing how data were obtained on stem shrinkage and swelling for reporting in tables. Letter "A" designates the maximum stem diameter attained during the night: "B" the minimum diameter obtained during the day; "C" the point on the curve when the stem diameter returned to its early morning maximum value; "D" the point where the night curve begins to appear linear; and "A1" the maximum stem diameter attained during the following night. In the tabulated data, the third column is the time, "D"; the fourth column is the diameter at "A 1"' minus the diameter at "A"; the fifth column is the length of time represented by the length of line "AC"; the sixth column is the distance in mm at which point "B" is below line "AC"; and the seventh column is area "ABCA." 14 ALABAMA AGRICULTURAL EXPERIMENT STATION shrinkage from early morning until the minimum diameter during the day, and (4) the area ACBA, or the integrated value of shrinkage in millimeters and duration of shrinkage in hours. The area ACBA was determined with a planimeter on the computerdrawn plots. A description of the data acquisition system and magnetic tape files developed can be found in Appendix I. Time Course of the Experiment Cotton seed were planted on May 2 in two hills equidistant from the front and rear walls, and approximately 30 cm from a side wall. Plants were thinned to one per hill (two per bin) a few weeks later. Plants were sprayed regularly for insects, especially early in the growing season. Bins were watered every few days to prevent drought from affecting root distribution or top growth before July 4. On July 5 and 6, all six bins were fitted with metal covers around the plants 5 cm above the soil surface and sloped to shed rainwater. The hole in the metal cover for each plant was lined with soft cloth to prevent injury to the bark and to keep excessive rainwater from running down the stem during storms. On July 8 routine measurements were begun. Net radiation, Fritschen (7), was monitored over a clipped grass sod about 3 m (10 feet) from the bins at 2-min. intervals. Ambient wet and dry bulb temperatures were recorded at 20-min. intervals. Plant height was measured daily. Plant water potential, soil water content, and rooting density were determined three times weekly. Measurements of Class A pan evaporation, daily total wind speed and direction, and 6-hr. temperature and relative humidity were obtained from the U.S. Weather Bureau station less than 1.5 km (1 mile) from the rhizotron site. The well-watered control (Bin 8) was irrigated whenever the soil water potential in any layer reached -1 bar. The soil in the 55-cm treatment (Bin 6) was irrigated twice and received 20 liters on August 4 and 80 liters on August 25. The other treatments received no water after July 6. Each LVDT was moved about 10 cm higher on the central stem and recalibrated on July 31 or August 1. Except for Bin 4,which was terminated on August 11 because their plants became chlorotic, the experiment was terminated on September 5. WATER RELATIONS of COTTON 15 RESULTS AND DISCUSSION Compaction Treatment, Bin 2 Bin 2, which contained Cahaba loamy sand soil with a compacted layer (bulk density 1.5 g/cm3 ) from about 15 to 25 cm deep, was not irrigated during the experimental period. Plant height increased almost 1.7 cm/day from July 7 to August 12, then increased 2 cm during the next 6 days. After that, height remained stable. Stem diameter increases followed the same pattern. Whenever water content of a particular layer decreased below about 0.07 cm3 /cm 3 , uptake rate from that layer decreased. In general, rooting density also decreased as water content of a particular layer decreased below 0.07 cm 3/cm 3 . Total root length and length of roots in soil wetter than -1 bar are presented in Table 1. When the experiment was terminated on September 5, the two plants had a total of 401 leaves and 132 bolls (Table 2). 15-cm Treatment, Bin 4 Bin 4 contained 173 cm of Dothan sandy clay loam soil (pH 4.6) as a subsoil material covered with 15 cm of Cahaba loamy fine sand surface soil. This treatment simulated a prevailing field situation with a plow layer limed sufficiently to raise pH to 6.0, but with the subsoil sufficiently acid for the aluminum ions to be highly toxic to cotton roots, Adams and Pearson (2). Soon after emergence, plants in this compartment became stunted as compared with those of all other treatments. Thereafter, these plants were shorter and yellower than all other plants. Some factor other than water stress apparently caused the reduced growth because plant water potential and stem shrinkage values were about the same as for well-watered plants. However, the plants stopped growing August 1. In all other bins, cotton growth ceased only when the plant root systems did not extract sufficient water to maintain low plant water stress (high plant water potential). Some roots penetrated at least 15 cm into the acid subsoil. No soil water contents were measured in this compartment because the acid soil layer was so close to the soil surface. The maximum total root length (Table 1) was less than half that of any other treatment. TABLE 1. TOTAL ROOT LENGTH AND ROOT LENGTH IN SOIL WETTER THAN -1 COTTON AT THE AUBURN RHIZOTRON, 1972 BAR FOR ALL BINS CONTAINING I-m Bin No. 2 Total rout Bin No. 4 Total root Bin No. 5 Total Root lngsoi Bin No. 6 Total rout Bin No. 7 Total root length Root >-1lbarb 0.0 0.0 0.0 0.50 0.93 1.23 3.52 4.51 8.19 10.28 13.59 17.63 21.19 21.86 23.65 23.09 17.32 20.28 11.58 8.68 5.40 length in soi Bin No. 8 Total root lengrthb length Root length in soil >-1 bar 1.54 1.64 2.66 3.70 5.30 8.32 9.34 10.67 14.86 17.10 20.13 22.30 22.85 19.85 14.15 0.0 0.0 0.0 0.0 0.0 0.0 Root lesoil lnta>-1 1.75 2.76 3.46 4.33 4.82 5.07 4.73 5.16 5.55 5.02 5.62 4.82 3.04 rout length gh bar cm X100.93 1.38 1.75 2.70 3.18 4.34 1nsi length baroi >-1ba 3.06 3.23 3.39 3.73 3.65 5.01 6.45 7.61 9.96 11.46 1.75 12.87 13.65 11.03 9.32 1.35 0.80 4.65 3.82 3.00 3.16 June 26 30 July 3 7 10 14 17 21 26 31 Aug. 4 7 11 14 18 21 25 27 30 Sept. 1 5 1.54 1.64 2.66 3.70 5.30 8.32 9.34 10.67 14.86 17.10 20.13 22.30 22.85 23.76 23.16 19.73 15.74 12.01 9.28 7.91 4.49 0.93 1.38 1.75 2.70 3.18 4.34 5.31 6.35 10.04 15.21 16.26 19.55 24.84 ---- 22.64 ---- 23.24 ---- 5.31 6.35 10.04 15.21 16.26 19.55 24.84 22.64 23.24 11.79 4.60 2.51 2.27 2.11 2.27 ---- 14.88 ---- 18.51 ---- 11.69 ---- 8.68 5.44 22.57 3.06 3.23 3.39 3.73 3.65 5.01 6.45 7.61 9.96 11.46 10.75 12.87 13.65 11.03 9.32 5.33 2.45 4.65 3.82 3.00 3.16 0.0 0.0 0.0 0.50 0.93 1.23 3.52 4.51 8.19 10.28 13.59 17.63 21.19 21.86 23.65 23.09 17.32 20.28 15.10, 10.98 7.69 -1 bar. 0.73 0.84 1.12 1.56 1.94 2.98 3.51 4.95 7.05 10.56 12.00 15.66 18.75 17.09 19.07 19.35 17.82 22.27 19.20 16.93 13.35 r 3.'Ii C -1 C x m 9.0 1.z z rn a No water contents were measured, so no determination possible on roots in soil wetter than -I OI ZI b Water content at all depths always greater than at -1 bar. WATER RELATIONS of COTTON 17 155-cm Treatment, Bin 5 Bin 5, which contained 33 cm of Dothan sandy clay loam soil (pH 4.6), covered with 155 cm of Cahaba loamy fine sand, was not irrigated. Plant height (Table 3) increased almost linearly with time until August 15, and then increased 1 or 2 cm over the next 5 days. Volumetric water contents and rooting densities are presented as functions of depth and time in tables 4 and 5, respectively. Substantial rooting and water extraction occurred at least 10 cm into the acid subsoil material. The total root length equaled the root length in soil wetter than -1 bar (Table 1) through August 21, then total root length started to decline and the plant height growth rate decreased. This occurred just as boll formation was starting. When the experiment was terminated on September 5, the two plants had a total of 568 leaves and 95 boils (Table 2). 55-cm Treatment, Bin 6 Bin 6 contained 133 cm of Dothan sandy clay loam (pH 4.6) covered with 55 cm of Cahaba loamy fine sand. Plants grown in Bin 6 were first to develop water stress. At that time (July 27), about 80 to 90% of the available water was extracted to a depth of 70 cm, even though the well-limed and loosened soil stopped at the 55-cm depth. This 70-cm depth of soil held about 14% available water - equivalent to a 10-cm (4-inch) depth of water. The soil was irrigated twice. Plant height (Table 6) increased almost linearly with time until July 27, then increased again for a few days after the soil was irrigated on August 4. Volumetric water contents and rooting densities are presented as functions of depth and time in tables 7 and 8, respectively. Substantial rooting and water extraction occurred at least 20 cm into the acid subsoil material. The total root length equaled the root length in soil wetter TABLE 2. LEAVES AND BOLLS PRESENT ON SEPTEMBER 5 FOR THE VARIOUS COTTON PLANTS IN THE EXPERIMENT Bin 2 Leaves 237 Left plant Open bolls 3 0 6 5 2 Closed bolls Leaves Leaves 164 232 254 234 653 Right plant Open bolls 8 0 3 2 3 Closed bolls 61 38 49 53 259 . 60_ 57 52 67 186 LI^ II--L-l -- 4 5 336 155 6 7 258 8 492 Iinn~rlTT ~rrrf~crfima TABLE 3. SUMMARY OF PLANT ToP MEASUREMENTS MADE DURING THE 1972 GROWING SEASON FOR COTTON PLANTS OF BIN 5 AUBURN RHIZOTRON Date July Height cm Duration of Daily Duration Maximum of nighttime increase Sshrinkagesrnkg in linear phase dia rshrinka dmeter TimeTTime (a.m.) Water diameter shrinkage potetial a.m. poten shrnrinkmeauredmeasue mm-hr. X 10 -Bars Hr. Water -BarsHr. Ten(pm. Hr. mm Hr. mm X 10' Left plant 7 9 10 11 12 13 14 15 16 28.4 29.3---- 8 30.5 31.0 31.5 32.6 33.6 36.0 37.5 37.8 3.3W 2.0W 2.3W 2.3W 8.3E -- LVDT not installed---------------- 0700 0705 0700 -- 11.3W* 11.0 1440 1425 w E** -- 9.3E - 1434 -- 17 18 19 20 38.2 40.2 0711 1000 11.3E 1401 39.5C 3.0 W --------- 0703 0714 ---- 8.7 W -- --- 1415 --- 42.5 21 22 24 25 45.4 47.0 49.0 49.5--55.5------- 2.0 W -- -- - ----- 26 2.0 W 53.5 ----- W 2.0 0709 0710 0708 23 11.0 W 48.5 ---- 1405 --- m X m 13.3 W 11.0 W 11.7 W 1425 -1414 1419 28 29 27 57.1 1.3 W -- Z 30 31 58.6 61.461.6 1.0 W 0711 9.3 W 1406 Z Aug. 1 2 3 4 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Sept. 1 2 3 4 5 5 cm 62.7 64.5 66.0 67.8 68.6 71.0 72.5 73.4 75.0 76.4 76.5 78.0 79.5 79.0 79.0 80.6 80.0 80.3 80.1 80.0 81.2 80.6 80.7 80.2 81.0 81.0 80.1 80.5 80.9 81.3 81.6 cm 80.2 80.6 80.8 80.5 80,5 Hr. mm Hr. mm X 10$ mm-hr. X 10 -Bars Hr. 0714 -Bars Hr. 1422 .7p 1.7W 2.0W 2.3W 2.3 W 2.3W 4.7 W 4.0W 5.3W ----------- ------- V DT not installed-----------------L 80'. 1 -----------------------------LV D------____ 10.0w 10.0w 12.3W 12.3 W 15.3W 18.3 W 19.0W 19.0W 24.7W --------- 0711 0711 0714 0710 0712 0706 0710 - -- 1410 1406 1409 1404 1414 1404 1414 1409 .-m m .Ior z I A 0 -I z --- lO.E 8.3 E 17.3 W 11.7 E 14.0 W 0710 -------- 0714 0842 0705 0703 Hr. 0710 26.7 W 28.0 W ---- 1414 31.3 W -Bars 1413 Hr. 1408 Hr. mm Hr. mm X 10' mm-hr. X 10 -Bars 14.7 E 19.3E 32.7 W 32.7W 0713 1406 (Continued) r iN TABLE 3 (Con't.). SUMMARY OF PLANT ToP MEASUREMENTS MADE DURING THE 1972 GROWING SEASON FOR COTTON PLANTS OF BIN 5 AUBURN RHIZOTRON Daily Duration of ,.al Duration Date Height nighttime linear phase July 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 cm 29.1 29.5 30.0 30.5 32.3 33.9 34.7 36.5 39.5 39.9 41.7 43.4 45.3 47.7 50.0 52.4 55.0 57.5 59.8 62.5 64.9 68.0 70.3 72.4 73.6 Hr. dimte shrinkage ineermeasured mm Hr. inrese of 'shrinkage Maiu Time- Time Time (p.m.) diametr Wer (m)ater potential shrinkage potential a.m. potential potential p.m. measured mm X 10' mm-hr. X 10 Right plant 10.4 2.8 1.2 3.2 10.8 6.4 10.8 2.0 4.4 10.0 6.8 7.2 3.6 7.2 2.8 10.8 1.6 8.0 6.8 -Bars Hr. -Bars Hr. 0.0 9.8 9.8 9.6 10.4 9.8 8.0 11.0 10.4 10.1 11.7 11.0 10.1 13.7 10.7 14.5 10.6 14.5 12.9 17.4 ---.023 .081 .177 .246 .255 .180 -.133 .170 .250 .151 .152 .143 17.9 10.4 8.0 6.3 7.1 11.9 ---- 9.8 4.0 1.6 0.5 1.2 7.5 3.3 7.4 0.7 2.8 6.5 5.3 5.2 0.9 3.7 0.4 5.8 0.2 2.4 a- 2.7 W 0718 11.3E 1453 r 2.0 W 2.7 W 3.0W 4.7W 1.7 W 1.7W 1.0W 0.7W 0716 0734 0728 0742 0734 0732 0735 0738 a C 11.0 11.2 8.0 9.3 12.2 11.5 11.5 ---- 3.3 8~.3 4.6 9.0 1.4 5.3 10.3 E 6.0W 11.3W 12.0W 12.3 W 10.3W 9.3W 1425 1842 1438 1435 1448 1438 1447 In I- C x -v 'i .358 .446 .366 .285 .349 aI OI 0 Aug. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Sept. 1 2 3 4 5 West cm 75.8 77.0 78.1 80.3 82.4 84.6 86.6 88.8 90.8 92.3 94.0 95.0 97.0 97.0 99.0 99.6 99.0 100.3 100.8 101.0 100.9 101.4 101.2 101.0 101.0 101.0 100.8 101.0 101.2 101.4 101.2 cm 100.9 101.4 101.4 101.4 101.0 * * East Hr. 11.4 12.3 11.4 11.4 10.1 9.8 10.3 11.7 12.8 7.9 7.9 7.4 6.3 0.0 7.6 5.0 7.9 8.0 5.8 5.8 5.0 5.4 3.9 3.2 5.5 5.5 5.5 Hr. 0.0 0.0 0.4 mm Hr. 11.3 mm X 10' 6.4 2.0 1.6 mm-hr. X 10 4.4 0.4 0.4 1.9 0.9 7.4 6.2 9.6 5.2 9.7 12.7 17.6 25.9 11.9 45.6 49.3 39.9 38.2 52.4 41.4 56.8 64.8 48.6 69.2 -Bars 3.3 W 1.7 W 2.7 W 2.7 W 3.3W Hr. 0747 0739 0733 0734 0737 .- Bars 11.7w 10.3 W 13.3 W 12.7 W 12.3 W 11.7w 16.7 W 20.7 W 22.0 W 28.3 W 28.3 W B-I .322 .509 .517 4.7 2.4 6.0 10.8 10.1 9.6 1446 1436 m .518 .509 .375 .348 .223 7.2 --9.3 3.6 3.2 12.0 11.6 16.0 8.8 13.2 16.4 19.2 32.8 I- 17' 1445 1433 1434 1440 1426 1423 1434 1428 1432 z H .267 .224 .205 .143 .103 -.063 -. 036 -. 071 -.027 -. 018 -.045 -- +.027 027 -.035 -. -. 11.6 12.4 7.2 17.4 14.2 24.0 24.0 23.7 23.8 23.8 24.0 A 3.3W 4.7 W 5.3 W 11.7 E 11.7 E 20.7 W 10.0OE 0746 0741 0732 0731 0730 0818 0724 0726 0 ZI 22.0 40.4 44.8 44.8 39.2 51.2 44.0 53.6 044 .071 mm 24.019.6 24.0 24.0 Hr. 24.0 60.8 59.2 62.0 57.2 60.4 mm X 10' 59.6 mm-hr. X 10 8.7W -Bars 20.0W 32.7W 1432 Hr. 1429 Hr. 0731 -Bars 33.3W 20.0E 0735 32.0W 1424 L Ew 22 TABLE ALABAMA AGRICULTURAL EXPERIMENT STATION 4. VOLUMETRIC WATER CONTENT AS FUNCTION OF DEPTH AND TIME IN BIN 5, AUBURN RIIZOTRON, 1972 Depth 30 8 10 12 14 17 19 21 26 28 31 Aug. 2 4 7 9 11 14 16 18 21 23 25 27 30 Sept. 1 5 July .223 .213 .202 .190 .174 .162 .151 .124 .264 .217 .174 .114 .090 .081 .072 .068 .063 .056 .051 .048 .045 .041 .039 .036 60 .235 .220 .210 .204 .196 .190 .184 .170 .163 .169 .167 .134 .115 .099 .080 .072 .065 .056 .051 .048 .045 .041 .040 .037 90 cm /cm .265 .259 .254 .248 .240 .230 .220 .202 .196 .190 .185 .178 .156 .142 .127 .108 .095 .084 .070 .062 .057 .053 .048 .046 .041 .245 .238 .283 .228 .221 .216 .211 .201 .197 .189 .182 .175 .160 .146 .126 .101 .084 .070 .052 .045 .041 .037 .033 .031 .030 .253 .251 .248 .245 .241 .238 .234 .222 .217 .209 .202 .196 .180 .160 .139 .103 .083 .063 .045 .040 .088 .036 .034 .033 .082 .322 .345 .355 .357 .358 .357 .351 .347 .337 .342 .328 .345 .322 .325 .310 .297 .287 .284 .277 .280 .267 .262 .242 .242 .240 120 150 180 Total water use cm/day .27 .38 .47 .44 .57 .66 .54 .75 1.76 1.38 1.50 1.27 1.13 .94 .76 .42 .47 .33 .41 .13 .12 than -1 bar (Table 1) through August 18, although the total root length started to decline after August 11. Plant height reached its maximum August 18, although maximum root length occurred 7 days earlier. When the experiment was terminated on September 5, the two plants had a total of 409 leaves and 110 bolls (Table 2). Drying Control, Bin 7 Bin 7 contained 188 cm of Cahaba loamy fine sand which was not irrigated during the experiment. Plant height increased almost linearly with time until August 15. By August 25, water content was less than 0.08 cm 3/cm 3 at all depths, and rooting density was greater than 1.0 cm 3/cm 3 at all depths. Total root length and root length in soil wetter than -1 bar are presented in Table 1. When the experiment was terminated at September 5, the two plants had a total of 492 leaves and 127 bolls (Table 2). WATER RELATIONS of COTTON 23 TIME TABLE 5. ROOTING DENSITY AS A FUNCTION OF DEPTH AND IN BIN 5, AUBURN RHIZOTRON, 1972 Depth (cm) 30 60 .06 .10 .10 .15 .18 .26 .40 .55 .58 .63 .73 .76 .92 .94 1.02 1.07 1.15 1.22 1.32 1.42 1.50 1.48 1.58 1.43 1.41 1.10 .79 .98 .66 .45 .15 90 120 150 cm root/cm soil .06 .10 .13 .19 .21 .24 .21 .21 .21 .27 .27 .27 .40 .56 .72 .85 .87 .97 1.30 1.53 1.58 1.50 1.56 1.55 1.58 1.45 1.15 1.20 1.08 .79 .37 0 .03 .07 .07 .13 .10 .13 .13 .13 .18 .27 .29 .45 .61 .74 1.00 1.05 1.33 1.88 2.27 2.48 2.42 2.33 2.70 2.47 2.23 1.43 1.90 .97 .82 .40 0 0 0 0 .09 .09 .09 .14 .14 .18 .22 .22 .30 .46 .58 .90 .94 1.40 1.88 2.31 2.70 2.49 2.06 2.96 2.52 1.81 1.62 1.98 .86 .66 .23 165 0 0 0 0 0 0 0 0 0 0 0 0 .11 .11 .11 .11 .11 .11 .19 .27 .74 .66 .74 .74 .74 .74 .98 1.05 1.05 .98 1.05 180 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .11 0 0 0 June 26 28 30 July 3 5 7 10 12 14 17 19 21 24 26 28 31 Aug. 2 4 7 9 11 14 16 18 21 23 25 27 30 Sept. 1 ,,5 .31 .34 .34 .40 .48 .56 .64 .84 .95 1.20 1.38 1.40 1.72 1.97 2.09 2.12 2.14 2.50 2.48 2.57 2.50 1.93 2.52 2.12 1.73 1.60 .92 1.35 .79 .32 .32 A-~ Well-water Control, Bin 8 Bin 8 contained 188 cm of Cahaba loamy fine sand, which was watered sufficiently to prevent any layer drying to -1 bar soil water potential. Plant height increased almost linearly with time until August 16. After that date, height continued to increase, but more slowly than before. Volumetric water contents, water additions, and drainage were measured and used to calculate the daily water use. Total root length is listed in Table 1. When the experiment was terminated on September 5, the two plants in this compartment had a total of 1,145 leaves and 450 bolls (Table 2). In all other treatments the available water supply was greatly reduced or exhausted prior to August 15. Yields of the wellwatered treatment (in number of bolls) was twice that of any other treatment. TABLE 6. SUMMARY OF PLANT ToP MEASUREMENTS PLANTS IN BIN 6, MADE DURING THE 1972 AUBURN RHIZOTRON GROWING SEASON FOR COTTON Dt Hegt Julyi 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Datenightime eigh linear Duration of ngtie increase o in phase diamein shrinkag Hr. 8.4 9.2 8.4 9.9 12.2 mm Hr. 11.0 Daily Duratio- Maximum daee shrinkae dmtr shrinkag e mm X 10' mm-hr. X 10 Left plant 7.2 2.8 5.2 7.6 4.5 1.3 3.1 4.8 Time potential a.m. Water (a.m.) potential Hr. Time potential p.m. esrdmaue Water Tie(m. potential cm 36.8 37.5 38.0 38.5 39.5 43.0 44.6 46.0 48.3 50.0 52.2 54.5 55.1 58.2 60.8 62.5 -Bars -Bars Hr. .059 .131 .146 .193 6.3 9.6 10.7 ___ 3.7W 4.3 W 3.0 w 0703 0710 13.OW* 10.7 W 8.7 W 1445 1432 1436 1403 1845 1418 1412 1222 1432 1726 1822 1420 1708 1712 1852 1334 1424 1409 .I).I .Ir 0702 0715 1003 0707 0718 0712 14.2 11.4 10.1 ____ 12.1 13.7 .321 .215 ___ 19.6 22.0 13.0 17.6 2.3W 7.7E** 2.0W 1.7 W 12.7W 7.7W 12.7W 13.3 W 12.7 W .-I A C 7.9 11.4 .054 .080 11.9 23 24 64.5 66.0 10.8 11.3 8.4 8.0 13.6 5.5 4.0 7.4 1.3---W 8.7 W 0950 14.7 W 8.0 W 6.3W 13.0 W 11.0 W 10.7 W 9.3W 17.3 W 16.0 W m m 25 26 68.3 68.3 8.7 14.8 25.2 17.2 3.0 W 7.0 W 7.3 W 6.3W 2.7 W 2.0 W 27 28 29 30 31 69.1 71.0 71.1 72.8 72.5 9.2 9.5 9.8 15.9 --- .098 .187 -. 017 .223 .053 6.3 23.9 5.3 11.6 --- 13.2 32.4 6.8 25.2 5.2 38.0 2.0 13.4 9.3 W 0715 0922 1008 1045 z 0844 0714 0716 6.0 W z Aug. 1 2 3 4 cm 73.4 73.2 73.2 73.5 Hr. 7.6 9.2 10.1 mm .072 .143 .232 .125 .116 .161 .178 .134 .125 .125 .018 .053 -. 088 +045 -. 098 -. 124 -. 018 -. 080 -. 051 +.027 -. 054 Hr. 18.0 14.0 10.2 11.6 12.7 11.2 12.6 15.4 ___ 10.2 14.8 21.2 17.4 24.0 18.9 24.0 24.0 24.0 24.0 24.0 24.0 mm X 10' 19.6 21.6 15.2 10.8 11.2 11.6 15.2 16.8 10.0 14.8 21.6 19.6 33.2 30.0 56.8 58.4 46.8 42.0 mm-hr. X 10 18.0 16.1 7.2 7.7 7.2 8.1 10.4 12.3 6.2 9.8 20.3 16.6 32.7 16.7 65.7 71.7 47.1 52.6 47.3 36.5 57.5 29.5 25.0 41.1 -Bars 4.0W 1.3 W 6.0 W 2.3W 2.7 W 1.7W 3.0 W Hr. 0721 0715 0750 0715 0717 0714 0720 0711 -Bars 15.3 W 16.3 W Hr. 1425 1414 mI m r 5.4 74.3 5 9.3 74.2 6 9.9 75.1 7 8.8 75.8 8 7.9 76.5 9 76.9 5.4 10 77.8 11 11.4 78.5 12 7.1 78.5 13 6.0 77.7 14 4.4 79.3 15 7.7 79.2 16 0.0 78.0 17 7.1 79.2 18 0.0 78.6 19 0.0 77.5 20 6.6 79.3 21 5.5 78.2 22 4.4 78.4 23 0.0 78.1 24 78.0 25 78.1 0.0 26 0.0 77.5 27 8.5 78.2 28 77.7 29 30 31 77.7 Hr. cm Sept. 9.8 1 77.7 78.0 2 78.2 3 4 78.0 5 78.0 Add 4 cm for true height. 15.0W 10.7 E 11.7W 11O0E 16.7 1426 1411 1414 1409 1417 1406 1417 1413 1418 0 0 0 3.7 W 5.3 E z 0715 19.7 W 0.0 22.9 15.1 24.0 .161 .054 .116 18.3 24.0 40.8 35.6 46.0 46.0 33.2 35.2 13.7 E 17.3 E 24.7 W 8.0OE 7.3W 0713 0717 0850 0707 0706 Hr. 28.0W 33.3 E 34.7 W 18.3W 1416 Hr. 1411 mm Hr. ---- --- mm X 102 22.8 mm-hr. X 10 ---- -Bars 8.3 W -Bars 22.7 W 0713 10.0 E 0716 12.3 W 1409 (Continued) N' 0% TABLE 6 (Con't.). SUMMARY OF PLANT ToP MEASUREMENTS MADE DURING THE 1972 GROWING SEASON FOR COTTON PLANTS IN BIN 6, AUBURN RIIZOTRON ,.al Duration of Duration Date Height linear nighttime rae of phase dimeter shrinkage Mxmm shrinkage dianme~ shrinkage Time- Time Time Wtr (m)Wter potential a.m. poentiald potential p.m. potential measured (p.m.) July 7 8 cm 28.6 29.3 Hr. 8.2 6.6 11.2 11.5 11.0 mm Hr. mm X 10' mm-hr. X 10 -Bars Hr. -Bars Hr. Right plant 9 10 11 30.3 31.0 32.0 11.0 .173 .164 .132 .166 .162 .114 7.4 9.6 10.5 10.7 12.4 12 13 14 15 16 33.9 36.0 36.5 39.6 42.0 8.7 10.6 7.6 2.4 5.6 4.8 5.2 12.4 12.8 8.4 1.2 7.2 10.8 12.8 17.2 16.4 5.6 1.0 3.0 1.7 W 0720 0725 2.8 3.5 8.2 9.0 30W 2.7 E 5---2.3W ---11.3 W 1455 0718 0732 0724 10.OE 12.3W 12.3 W 1423 1434 1431 OiO 17 18 43.4 44.0 9.2 8.8 11.4 10.4 11.4 .107 .250 .401 .313 19 20 21" 22 23 24 25 26 27 46.4 47.2 49.8 51.5 52.5 54.9 55.6 56.8 57.8 13.5 11.8 5.0 9.1 9.3 3.8 0.5 3.8 5.9 - 8.4 9.2 9.0 10.6 10.4 .259 .205 .179 .214 12.2 12.6 9.0 --- 8.0 11.2 9.4 14.2 4.0 3.3 W 2.0W 0737 0730 15.7 W 14.3 W 16.0W m 3 -I 1445 m 28 29 30 31 54.5 60.0 61.0 61.5 9.8 12.6 10.1 ---- 12.1 .214 6.4 .259 11.0 .161 --10.4 24.4 11.6 21.6 26.8 3.7 W 2.3W 1.8W 0727 0733 0734 1435 13.3 12.4 1442 ZI z Aug. 1 2 3 4 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 25 26 27 28 29 30 31 Sept. 1 2 3 4 5 *West 5 cm 62.3 63.5 64.0 64.5 65.0 Hr. 9.5 9.5 9.5 9.9 9.9 9.2 9.5 10.4 10.9 8.7 mm .098 .187 .304 .232 .205 .134 .134 .186 .151 .125 .000 .009 -. 126 +.045 -. 134 -. 098 Hr. 16.6 mm X 100 18.8 18.0 15.2 6.4 7.2 9.6 10.8 12.8 10.4 16.8 21.6 23.2 44.0 35.2 58.4 54.4 41.6 mm-hr. X 10 16.8 13.3 5.3 4.8 4.5 8.2 4.7 8.8 5.8 12.6 21.5 25.1 56.0 25.3 73.4 67.8 43.4 55.6 -Bars 2.7 W 4.0W 3.3 W 2.0 W 2.0 W Hr. 0743 0734 0729 0730 0734 0744 0734 0728 0728 0735 0915 0720 0722 Hr. 0728 -Bars 17.7W 13.3 W 14.0 W 12.3 W 8.3 W 15.3 W 18.0 W 22.0 W 28.0 W 32.7 W 34.0 W Hr. 1443 1433 1442 1428 1430 1435 1433 1420 1431 ,00 7M - 65.9 67.5 69.0 69.5 70.3 71.5 72.8 72.0 72.0 72.2 13.3 10.0 10.2 11.8 12.9 10.7 10.4 10.7 16.3 II' m - z 0 5.8 72.4 6.6 24 73.2 73.1 73.3 73.3 72.5 72.8 73.0 72.6 72.5 73.0 72.4 73.7 5.7 0.0 5.2 0.0 0.0 9.3 7.9 6.8 7.9 7.7 5.0 8.4 +.018 20.9 22.8 24.0 23.2 24.0 23.5 24.0 24.0 3.3 W 2.3 W 5.3 W 14.0 E 15.0OE 24.7 W 7.3 W 6.7 W 0 0 z +.09,8 -. 062 -. 054 -. 018 -. 045 .040 24.0 24.0 24.0 17.4 24.0 42.8 40.4 39.2 39.2 40.4 27.6 32.4 51.5 50.9 48.5 29.6 33.7 1433 --- 17.7 W -Bars 22.7W 1429 Hr. 1426 --- -- --- - 9.5 cm 72.8 73.6 73.5 73.6 73.6 East Hr. mm Hr. mm X 102 mm-hr. X 10 -Bars 9.3W 8.7 E 0732 12.0W 1420 28 28 ALABAMA AGRICULTURAL EXPERIMENT STATION TABLE 7. VOLUJMETRIC WATER CONTENT AS FUNCTION OF DEPTH AND TIME AND TOTAL WATER USE AS A FUNCTION OF TIME FOR BIN 6, AUBURN RHIZOTRON, 1972 30 July 8 10 12 14 17 19 21 24 26 28 31 Aug. 2 4 Irrigated 7 9 11 14 16 18 21 23 25 Irrigated 27 30 Sept. 1 5 .228 .216 .204 .191 .168 .153 .111 .087 .072 .062 .054 .051 .047 .240 .185 .147 .097 .075 .054 .040 .037 .036 .317 .190 .160 .105 45 .264 .247 .228 .211 .184 .165 .137 .086 .072 .062 .054 .051 .047 .257 .200 .157 .097 .075 .054 .040 .037 .036 .274 .212 60 .279 .267 .249 .234 .204 .180 .150 .105 .093 .084 .075 .071 .069 .257 .200 .162 .108 .085 .072 .061 .060 .053 .225 .216 Depth 75 cm'/cm3 .285 .278 .270 .265 .250 .241 .234 .221 .213 .205 .193 .185 .177 .269 .247 .220 .189 .174 .172 .153 .150 .148 .206 .227 90 .322 .322 .318 .805 .303 .317 .321 .300 .293 .290 .297 .298 .299 .298 .290 .289 .288 .287 .287 .280 .277 .278 .274 .275 120 .337 .334 .333 .331 .329 .327 .326 .324 .323 .322 .320 .319 .318 .317 .316 .315 .313 .312 .312 .311 .3101 .309 .309 .308 .307 .307 180 .337 .403 .401 .399 .407 .420 .419 .380 Total uster cm/day .397 .383 .390 .391 .380 .375 .382 .372 .385 .382 .390 .375 .384 .375 .380 .387 .390 .381 .24 .52 .47 .59 .62 1.12 .78 .48 .35 .23 .16 .17 1.84 1.38 1.22 .78 .59 .36 .10 .09 1.52 .94 .93 .182 .120 .195 .132 .213 .199 .275 .278 Large quantities of water are absorbed by plant roots from the soil reservoir. The quantity of water usually considered available to plants from a particular profile depends upon the amount of water retained after drainage for 2 or 3 days (field capacity), the amount retained by soil when the plants can no longer recover overnight (wilting point), and the depth of rooting. Significantly changing the available water capacity (field capacity minus wilting point) of a soil is quite difficult, 'but rooting depth can often be increased by correcting adverse soil conditions (Pearson (11); Taylor et al. (16). Our results indicated that cotton top growth was reduced to zero whenever the leaf water potential at sunrise was less than -7.6 bars, or whenever the leaf water potential at 2 P.M. was less than -21.1 bars. With the same accuracy, plant water stress at the time growth became zero, could be, determined in terms of the maximum stem shrinkage, the duration of shrink- WATER RELATIONS of COTTON TABLE 8. ROOTING DENSITY OF COTTON AS A TIME IN BIN 6, AUBURN RHIZOTRON, 29 FUNCTION 1972 OF DEPTH AND Depth (cm) 75 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .19 .19 .59 1.05 1.05 .74 .98 .66 .66 .66 .74 .59 .82 .51 .19 90 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 15 June 26 30 .43 .43 .51 .51 .59 .59 .59 .66 .59 .74 .74 .90 1.05 1.43 1.66 1.58 1.66 1.81 2.03 2.24 2.39 2.39 2.10 2.17 1.51 .74 .59 1.81 1.36 .66 .82 28 30 July 3 5 7 10 12 14 17 19 21 24 26 28 31 Aug. 2 4 7 9 11 14 16 18 21 23 25 27 30 Sept. 1 5 1.66 1.88 1.66 1.73 1.73 1.73 1.66 2.17 2.24 2.53 2.46 2.60 2.87 2.81 3.01 2.94 3.01 2.46 3.15 3.01 3.08 2.10 2.38 1.88 .90 .19 0 .59 .27 .51 .98 60 45 cm root/ cm, soil 0 .74 0 .83 0 .82 0 .90 .98 0 1.13 0 1.13 0 0 1.58 .10 1.81 .10 2.60 .11 3.01 .27 3.28 .82 3.87 1.05 3.93 4.73 1.21 4.73 1.36 4.67 1.51 4.06 1.43 4.79 1.36 1.58 4.67 1.51 4.61 4.00 .98 1.05 3.54 2.94 .98 .59 1.28 .74 .59 .43 .66 .66 .43 .66 .51 .59 .43 .51 age, or an amount of shrinkage-duration parameter. In addition to these factors relating stem or top growth to plant water status, our results show that plant water status also has very important effects on root systems. drought in Alabama during various months of the growing season and at various available water supplies. Data on available water capacity was combined with theirs on drought-day probabilities to estimate the depth of rooting necessary for high yields. Admittedly, these data must be rechecked in experimental trials before farmers undertake large-scale profile modification. The drought probability data for Auburn, Alabama shows that in 9 out of 10 years at least 20 days of seasonal drought should be expected with a soil water storage capacity of 10 cm in the rooting zone. If the Ward et al. (17), calculated the probability of plants suffering 30 ALABAMA AGRICULTURAL EXPERIMENT STATION depth of limed and loosened soil is decreased to 30 cm (45-cm total depth of rooting), the available water storage capacity is reduced to 6.3 cm and, in 9 out of 10 years, at least 32 days of seasonal drought should be expected. Considerable power is required to lime and loosen the soil to a 60- to 75-cm depth, and in some soils the loosening process is quite temporary. Large quantities of lime would be required to increase soil pH from 4.6 to 6.0, but the available water supply in the 85-cm rooting zone would be 12 cm, and in 2 out of 10 years plants would suffer no drought. In half of the years the plant would suffer less than 35 days drought. CONCLUSIONS Data collected during this experiment allow estimates of the available water capacity and rooting depth for these sandy soils. Thus, the minimum depth of rooting necessary for high yields of cotton during most growing seasons can be estimated. Results (Bin 4) show that an acid (pH 4.6) subsoil at the 15-cm depth reduced growth rate of cotton soon after emergence. These data indicate that some factor other than plant water stress caused a reduction in growth. Therefore, regardless of the frequency of rain or irrigation the depth to an acid soil layer should be greater than 15 cm (6 inches) if maximum cotton yields are desired. Apparently, where root-restricting layers are present, long-term cotton yields would be increased by profile modification to at least 60 cm, and probably to the 75-cm depth. Although long-term yields would be increased by profile modification, the farmer may not be able to justify the additional expense to create soil conditions necessary for additional yields. Therefore, the farmer should carefully consider whether or not the increase in yield is worth the additional cost. Data from the well-water control (Bin 8) indicate that for best cotton yield the plant must have a continuous water supply during boll formation. Water stress and plant aging reduce the growth of new roots, and thus reduce the ability of the root system to supply water to plant tops. These drought-associated rooting changes apparently cause earlier closure of stomates while light for photosynthesis is optimum. The root-shoot interactions result in a progressive degradation of the water-supplying ability of the root system. The basic data presented in this bulletin and appendices may WATER RELATIONS of COTTON 31 be of use to research workers interesting in simulating water uptake by root systems or plant growth as affected by various environmental factors. Because of plant modelers' possible interest in this data, weather data for a station located about 1.5 km from the rhizotron is included in Appendix II. In addition, Appendix III includes a list of summaries of publications for which data were collected wholly or in part at the Auburn rhizotron. These publications will provide further analyses of various plant growth experiments and may be helpful as background material. 32 ALABAMA AGRICULTURAL EXPERIMENT STATION LITERATURE CITED (1) ADAMS, F., R. W. PEARSON, AND B. D. Doss. 1967. Relative effects of acid subsoils on cotton yields in field experiments and on cotton roots in growth chamber experiments. Agron. J. 59:458-456. (2) ADAMS, FRED AND R. W. PEARSON. 1971. Differential response of cotton and peanuts to subsoil acidity. Agron. J. 62:9-12. (3) BROWN, K. W. AND NORMAN J. ROSENBERG. 1969. Computer program for plotting time-dependent data with instruction and examples. Univ. Nebraska Bull. MP 23. Nebraska Agr. Exp. Sta., Lincoln, Nebraska. (4) BROUWER, R. AND C. T. DEWIT. 1968. A simulation model of plant growth with special attention to root growth and its consequences. Pages 224-242 in W. J. Whittington, ed. Root growth. Plenum Press, New York. (5) DOERING, E. J. 1965. Soil-water diffusivity by the one-step method. Soil Sci. 99:322-326. (6) Fiscus, E. L. AND M. G. HUCK. 1972. Diurnal fluctuations in soil water potential. Plant Soil 37:197-202. (7) FRITSCHEN, L. J. 1963. Construction and evaluation of a miniature net radiometer. J. Appl. Meterol. 2:165-172. (8) KLEPPER, BETTY AND R. D. CECCATO. 1969. Determination of leaf and fruit water potential with a pressure chamber. Hort. Res. 9:1-7. (9) KLEPPER, BETTY, V. DOUGLAS BROWNING, AND HOWARD M. TAYLOR. 1971. Stem diameter in relation to plant water status. Plant Physiol. 48:683-685. (10) LANG, A. R. G. AND F. M. MELHUISH. 1970. Lengths and diameters of plant roots in non-random populations by analysis of plane surfaces. Biometrics 26:421-431. (11) PEARSON, R. W. 1966. Soil environment and root development. Pages 95-126 in W. H. Pierre, Don Kirkham, John Pesek, and Robert Shaw, eds. Plant environment and efficient water use. American Society of Agronomy and Soil Science Society of America Press, Madison, Wis. (12) PEARSON, R. W., L. F. RATLIFF, AND H. M. TAYLOR. 1970. Effect of soil temperature, strength, and pH on cotton seedling root elongation. Agron. J. 62:243-246. (13) STANSELL, J. R., BETTY KLEPPER, V. DOUGLAS BROWNING, AND H. M. (14) TAYLOR. 1973. Plant water status in relation to clouds. Agron. J. 65:677-678. TAYLOR, H. M. 1969. The rhizotron at Auburn, Alabama - A plant root observation laboratory. Auburn Univ. Agr. Exp. Sta. Circ. 171. Measurement of soil-grown roots in a rhizotron. Agron. (15) TAYLOR, H. M., M. G. HUCK, BETTY KLEPPER, AND Z. F. LUND. 1970. J. 62:807-809. (16) Root development in relation to soil physical conditions. Pages 55-77 in D. Hillel, ed. Optimizing the soil physical environment toward greater crop yields. Academic Press, New York. (17) WARD, H. S., C. H. M. VAN BAVEL, J. T. COPE, JR., L. M. WARE, AND H. BouwER. 1959. Agricultural drought in Alabama. Bull. 316. Agr. Exp. Sta. of Ala. Polytech. Inst., Auburn, Ala. TAYLOR, H. M., M. G. HUCK, AND BETTY KLEPPER. 1972. WATER RELATIONS of COTTON 33 APPENDIX I Monitoring Environmental Conditions: Data Acquisition, Reduction, and Storage To facilitate describing root growth and function as influenced by measurable soil properties, the physical environment of the soil in each rhizotron bin was monitored by a network of transducers during the entire experiment. Additional measurements describing the aboveground microclimate were made and recorded on master magnetic tape datasets, which are available for use by other investigators wishing to analyze the accumulated data. A. Hardware 1. Transducers a. Temperature. The temperature of the soil in each rhizotron compartment was monitored by a network of thermistors buried at 30-cm depth increments in each bin. Commercially-available thermistors from Fenwall Electronics, Inc. 1 were factory-selected for uniformity of temperature response curve. The manufacturer guaranteed absolute accuracy to within 0.2 C over a temperature range of 0 to 80 C, using factory-supplied calibration data applicable to each interchangeable unit. Statistical regression analysis of the resistance-temperature could be obtained from measured thermistor resistance by substitution into the following equation: T = 236.986744 + (0.00002832 X r) + (0.4424 (47.869563 X loglo (r)) X 1/sin (r X 10-5)) (1) where r is measured thermistor resistance in ohms, and T is the indicated temperature in degrees centigrade. The thermistors were embedded in epoxy resin or sealed into heat-shrinkable tubing and buried in the rhizotron compartments at the beginning of the growing season. Additional thermistors embedded in epoxy resin monitored ambient air temperature, wetbulb temperature, and temperature in the rhizotron walkway. b. Net radiation. A Fritschen (7) net radiometer was maintained over clipped grass sod at a distance of approximately 3 m from the rhizotron compartment and 1 m above the sod. The integrating hemisphere was kept under slight positive pressure by a continuous stream of filtered air blown in through an aquarium pump. The factory calibration value of 8.05 mv/ly was used without further experimental verification. c. Oxygen concentration. Oxygen concentration in the air-filled pore spaces of the soil in the compaction treatment (bin 2) was monitored by Chem-tronics Model GP-10 Gas Phase Oxygen Transducers 1 installed in inverted 100-ml glass diffusion chambers. Duplicate transducers were installed just below the compacted layers of bin 2. An additional pair of diffusion 1 Mention of a trademark name or a proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture, and does not imply its approval to the exclusion of other products that may also be suitable. 34 ALABAMA AGRICULTURAL EXPERIMENT STATION chambers was installed in the center of the compacted zone with one transducer adjacent to the glass window and the other in the center of the bin. Shielded leads in waterproof cable connected each transducer to the Digital Data Acquisition System (DDAS), which recorded the 0- to 10-mv output voltages from each transducer. Calibration was accomplished at periodic intervals by flushing the diffusion chambers with N 2 gas supplied from a cylinder, or with ambient air (21% oxygen) through capillary tubes leading to the surface of the soil. 2. Data Acquisition System Hardware A Vidar Model 5403-03 Digital Data Acquisition System (DDAS) 1 is installed in an instrument trailer adjacent to the rhizotron. The trailer is air-conditioned to keep ambient temperature and humidity within the DDAS manufacturer's specified tolerance limits. This DDAS is capable of reading analog data from up to 200 input channels (transducers) and converting it to digital form. The input can be either D.C. volts (± 10 my to ± 100 v full scale) or D.C. resistance (100f to 10Mf full scale) with resolution of ± 0.01% full scale range. Binary coded decimal (BCD) output from the system is recorded in IBM-compatible EBCDIC characters at a density of 800 bits per inch on a 9-track digital Incremental Magnetic Tape Recorder (ICMR). Because of frequent thunderstorms during the growing season, lightning protection as well as an auxiliary power source was essential to keep the system in operation on a continuous basis. Lightning protection was accomplished by installing a Joslyn Model 1201-02 lightning and electrical surge protector' between the DDAS and the power line. With this device, an impulse voltage of 20,000 volts is held to no more than 50 volts deviation from nominal output over 0.4 microseconds, and output returns to normal operating voltage within less than 0.7 microseconds. All transducer leads utilized multiconductor shielded cable between the various rhizotron compartments and the DDAS. They were buried to minimize interference and signal loss. With many data acquisition systems a temporary power interruption will cause all data to be lost from the time of the power failure to the time of resetting the digital clock and the ICMR. Power failures tend to occur during periods of heavy rainfall and rapidly changing temperatures, so that data lost for this reason will occur during the most critical times of an experiment. To prevent data loss, the clock for the rhizotron DDAS was ordered with a 100 kHz crystal time base so that it could be operated from a simple power inverter without precision frequency regulation. Both the digital clock and the ICMR were continuously run by a 300-watt Topaz inverter 1 which, in turn, was powered from a 12-volt storage battery. The battery was kept at full charge by a 15-amp battery charger supplemented by an automatic 8-amp battery charger which charged only when needed. The total cost of the inverter and charging components was approximately 10% that of commercially-available off-line power supply units with precision cycle regulation. In operation, the transducer inputs are grouped into blocks with similar functions clustered on consecutive channels, because each time the system WATER RELATIONS of COTTON 35 changes range or function, its scan time is increased. While auto-ranging is available for channels with widely fluctuating signal strength, it was not generally used because of the increased scan time required. An online paper tape printer and Nixie tube displays were available for setup or for checking output of a particular channel during an experiment. Two strip chart recorders with a total of 12 channels were used to monitor transducers and to provide feedback information to the experimenters about realtime changes occurring in the plants before computer dumps from the magnetic tapes were available. Because the rhizotron DDAS is a free-standing system without on-line computer support, the switching mechanism of the scanner requires that when any channel is scanned, all other channels in use must also be scanned. Thus, if one channel has a rapidly changing input which must be scanned frequently to monitor rapid fluctuations (e.g., net radiation, which varies with each cloud), all channels then in use must be scanned at the same frequency even though other channels (for instance, those monitoring soil temperature) change much more slowly. The result is an accumulation of redundant data at the magnetic tape from the slowly-changing input channels. As a result of recording the status of all channels each time any channel is examined, the tapes were filled sooner than if only essential information was recorded. During the 1972 growing season the DDAS was set to scan all 200 channels at 2-min. intervals. At the recording densities used, tape consumption was still less than two 1,200-ft. reels per week. After primary data reduction by a remote computer in a batch-mode operation, the original tapes could be returned to the rhizotron and reused for storage of additional data until consolidated into the master tape files by computer. B. Software 1. Primary data reduction After data collection intervals of 2 to 4 days, tapes from the rhizotron data-acquisition system were processed to remove redundant information and to build data files compatible with further studies. Using a file-oriented language (PL-1 on the Auburn University IBM 360/50 computer) millivolt values representing net radiation and stem diameter were copied at 2-minute intervals. Oxygen concentration, ambient air temperatures, and wet-bulb temperatures were recorded onto the master tape records at 20-minute intervals; soil temperatures were computed and recorded at 60-minute intervals. All other data on the field tapes were ignored. Information selected for further processing and storage was converted from the electrical units (volts or ohms) into the measurement units appropriate to the device monitored at this time. Stem diameter was computed from the millivolt output of each LVDT according to the calibration factor recorded daily. Net radiation was obtained from the factory calibration value of 3.05 mv/ly. Temperature was obtained from measured resistance by substitution into equation (1). Following conversion to appropriate units, the data was stored on magnetic tape files as a series of 80-character card-image records, using the 36 ALABAMA AGRICULTURAL EXPERIMENT STATION format of Brown and Rosenberg (3) as illustrated in Appendix Figure 1. As each field tape was processed by the primary data reduction program, the output data file was manually verified to be free from computational errors. Then each scratch tape was copied onto the end of a pair of master tapes. Duplicate or backup master tapes were useful in preventing errors introduced in the updating process. 331 023x.1I7+)4(2+n 152-03359+0261+;7(765+032()9+042031 5673+0726+063372+-1008+l1 3Th>-))c OR 1702'5 35 --'757+026 231+0299+0428+0560+0726+406372+1 0083+113+4 33 )76-'383 03113704437+041 720+03372+ 1007+- 1394X0+73-) )531317'4 2 17-+()'+1.40362-105-+0)262 +0(286+029+0428+05' 87-0 726+-06 7?+ I1T+3o4-303350-30834)242-0u3333+0288'3342b+06+0 51)263-(056+02 +262 +(7 698 10 C74-I)lL'-'?035-3343 172441 7+ 3-1 4+x)360-0385 T+02630i8341+(299+0483+056,+0)726-+0 871+ ^3t17024617-41+033633383-3 c,904?+0566+03726+08371+10(7+11+66038330051 3 3171)24') 1 74- l-+23 37079+7493+0428+40566+0726+08 71+1307+ 1 1671-33 i1 33350 03170?58017+4? o4+3 374-"!885+"7267+0482+0-21--y+04284-0560+7+ 371+ 1007+1 (.R3046-0()483 001 7(37521 7+4382+0332-0354+'3'62+0( 204-02+9+334284-086+378+371-13371133 333230344 -3' 0343. 1+0+30+038?3-004-5+-3?62+0366+-0?08'0428-3363'3+'3728'0371+1037+-1 36(3 'l:' 10 7 168q30)7-0()52 +1 17- 0l1025?8+1 '3337333^127'(0+7367-0334+243+8l84-224+21258+2552+2482+?31 7+2528+00332+)033) 0173033 32+?7(,3+2' 53+2610+25 324243+23737+2678+-2567+2-1 7+243=;+258314-2764+30)3+c33(03 383 7.)3()0;333+?(31+74,55+76,74+25'-4+? 2 7+2702+2761+265 1+2718+27-73+3000i+00003+0700+0000,3 301 7'3)33C)4-'44+2 7?c+2416+-'?5?+488+2710+2678+42596+2533+2803+000#)3 700+00+0")00 ()4 037005,3(+2'1852+816+42 763+2 74+27L1 2+?50+80+'747+265+2.(,04+04-0(0(+0000(4+00')0+03)03 75 +2695+72?0+25 73+2647+2 7'4+2h07+?23+7.562+-250 300(40303(0003344J0 345724+2141+21737+2634+2?' )5+2590+254()+00430+03000+333I +313033 430113740 ('0+7734+?' 704-2836+2578+2553+273(++272 1+23443+264 1+2841+0)0+3 3C+00 30+332)!( 33+33300 033703304- 9424-1+28334)508+283842244-2436+2821+24-4742327+2624+0003 +O03O+0+ 4337(33034+ 0+6?7084233364-3442247+07+3-36+42246+2575+2533+4333.3+003 +033+433333 0)1703'),11 ?5 0+1)551 +76221 964 +2241+2264+7621+ 34337031)3124~7-v7. +2 71'++7599+254-3+2515+-2 18+23633+27136+263)7+00000+3333+300 3317000)10-7 14+27344-2702+834- 63 2 730+267528202-7 74+7694+01)07+0 700 00 +423+4+42772+7631+03326+2?9+2-738+278+2-)77+767 1+2671+273+2617+000+070030 43 3737303]1 7+3430+3387)J374+03262+052 8+32'4-4-'34)42+0")6++077 5+08 71 +1 1 -31) 33+1-304? '170)04217+r+849+0433-n) 4+0322-0388+-03:+0428+400-7 +0725+()871+1(07+1167--3330-0343 04337;)33304533333+03033+ 33+(3 3+0261+?241+20374-2313+01224-0000+ 4237+01851-0344+8,)31 43431-403334 17+0+)C+04.331-005)9+)?61 +0~237+-0294+03423++3)+3725+03371+ 1033+ 1 1643358-0047 0317)_281 03173288,1 7+(+' +0 1+5427+-03537- 3330854+13251 -0.1)2c,93?+04?8+0566+0725+08371 + I037+ 116 7-001;-0.04? "34+0?2614+(31 304-0?99+'83+08t1+07285+08 71 +1 03.+ 1 146-3300332 0317004171)6+-? 0317030031)7+2171+23:565x1+?5 +21-)'706-2638+2 7333031 7+73342830 ?7 26.2-4+29587+000 000+071243+0300 (;:7+ 13 773')6417++358+(4,28- )61+0243,+0'37-2+02 )9+0 '28+0(A+1725+08731+1 +11( 015+ 5-333i-7347 1.1137)33117+0447043-03406.102614+0 3311 0317031217+74 7:17:)31347+).-.45'5."356+ 7 110 17 4A 338074-324 3+4 233+3334+3428+083 ,6+734 3771+775783~7112+C)2' '43+054-67+0726+0872+1008+116" 5+3840441 7?27+025+0425+06-072+071+103+ 1 160-')0) 7+0726+t)8 72+L 63342 1 18-73-3035 33730-3151 425c0(717+(0+ 2017;31617+0:)13+38437-')3355+)?83+;)383384-+3j34'+084-3+3726+373+ 3.317)3133 +303-+0333408443373 7(2)17+3C434+4435-133-4 +3217.58 3?5334+4-374-298'48284-3363 77+)294+04429+056: 42+,7567+016+187+107+1169-13363-3351 137+313346-77346-0354 +3 726+333724-13333+1168-0351-0)83 +4726+0872_+10336+11+-05036)336 043'04436-()0515+32583+041 7+3321+43+342+083-.'+43724+037+134+3 11733 -408052 ' :) 17113241 5+-1')0+04040303+ 00 +2 '+R+2 ?7+?O? 1 +1996 129+000:)+0(- 8+01 51 -"31153+ 5 382 0333703324 -2'9+-)429+0567+076+33372+1310)+13684 333-+'i335? 331 7,32417+()4306+04 37- )'74+1)?=)8+') 313+'))433!;+3419+053 7+(0726+05 03170324137443+()45)3-3)384+3255+4-3' 87)31) '-3)424-+05b87+0726+083724-10(76+1170-00386-0385 52+')4-28+0524+3030+()429+056-7+3726-033724-10135+11 7t)-31)32-0380 031 7;)301337+"7443+0431 3?+')+0-3 +')3333+(42490-3734(723+33372+10043+3170-0033803)37 ')-117()332 04+3-++28-') 0-33104 317+')4+31+35 12-;7152+J?35)+137331 4+01,?+0429+05647+0776+05372+1006+1 170-004 7-0088 0333)3721'7 174-+0437+04140"_13+325;3+0+40 72+1,)7.6+1164-300351 . 3103733637+3453+04583-338524 8334-43(33-3064-42+3367+3726+3312+1003411 70-3)055-0348 1):170)3)3337+474344-0)5?+)2)-3:,343+3)03+3)428+30567+3726+08724-3406+1170-333)03530 30311700)4:))7+1 483+;)445-,)')43,77,;+71o4031)44+40867+0372 7+372+1()-78+1170-()054-3382 K0 3 3* Cc a 2 3 4 5 6 7 8 9 10 II 12 13 14 App. Fig. 1. Example of the card-image record format used in compiling master tapes with information from all channels monitored by the data acquisition system. Following the time of observation, a card number is entered to identify the data in the 14 data-columns which follow. In the example shown, corresponding to August. 17, 1972, card 17 is entered in the master tape record at 2-minute intervals because it contains net radiation and stem diameter data which fluctuate very rapidly. Card 15, containing ambient air temperature, oxygen concentrations, wet-bulb temperatures, vapor pressure, and relative humidity appears at 20-minute intervals, while cards 1-14 with soil temperature arrays appear only at the beginning of each hour.. WATER RELATIONS of COTTON 2. Secondary data files 37 Because many different experiments or many different kinds of data are often recorded simultaneously on the rhizotron data acquisition system, short PL-1 routines based on Brown and Rosenberg's (3) card-image format were developed for examining a 'single (or only a few) variables as a function of time. CALCOMP plots of various parameters as a function of time were also prepared for study. Separate auxiliary files containing only microclimatic data or only stem diameter data have been prepared. An auxiliary file with only stem diameter and net radiation at 2-minute intervals (card 51) and at 20-minute intervals (card 52) is shown in Appendix Figure 2. 917 317 917 817 817 236511.?31 23851172? 2405110232 2429110232 2445110732 9275 9276 9276 9276 5?76 -57 -57 -57 -58 -56 257 248511:233 9?76 817 2465210233 9276 917 2489110233 9277 817 2505110234 9277 2529110284 9279 817 2545115234 9278 817 2565110734 9278 817 259110234 9279 917 3005111234 '270 817 9925117236 9289 817 3045117734 9284 x17 3065110215 9283 817 3065210035 92893 P17 308511234 9283 817 9195117239 9285 317 91201135 15110236 917 3165117234 929+ 91 ;317 3185110215 9734 317 320513073592979 817 25110 9 9294 317 32+5110235 9285 817 -55 117 8285 986 -55 -54 -54 -53 -5 -53 -53 -73 291 -73 -99 267 290 -60 -(2 ) -61) 260 -56 259 258 -57 257 -55 297 -94 297 -54 -55 257 -54 297 297 -52 261 261 261 262 292 262 261 261 261 261 790 265 261 ) - -57 -58 412243 7981 8211 9303 9241 780815728 -55 -57 -1012243 7931 8203 9303 9241 780815728 -44 -55 -9712243 7981 8203 9303 9241 779915728 23512243 7981 8211 9303 9241 77-'15728 -34 -52 -56 -51 3982243 7991 8203 9303 9232 779515728 -50 -5512243 7981 6203 9303 9232 779915719 0 -5512243 2°81 8203 9903 9232 779915719-1071 -50O-49 77812243 7981 8203 9303 9232 779915719 48112243 7981 8203 9294 9232 779'-15719-45-47 -22 -43 92212243 7991 82(3 9294 9292 779915719 -18 35 16512243 7981 8213 9294 9232 -41 -1712243 7991 8203 3294 9232 778915710 -49 -57 -41 12912243 7991 8203 9294 9232 775015719 -41 52312243 7581 8203 9794 9292 779915715 -50 38-40 35712252 7581 8203 9294 9232 779915719 -53 -41 32312249 7981 8203 9294 9232 779915719 -57 -6 89112249 7991 8203 9294 923? 779915719 0 95112249 7981 8209 9294 9232 779915719 -887 -55 -51 72012249 7581 8203 9294 929?779915719 -52 51 20512243 7990 8211 9303 9241 780815728 -49 -50 11112243 7990 8211 9393 9241 780835728 8211 9303 9241 773919728-50-50 55-53 59712243 7990)9273 9303 9292 774915728 -503-52 56617249 7930 8203 9303 9241 780815728 7561243 7990 8211 9309 9241 289815728-54-52 -50 -51 41612249 790 8211 9303 9241 780615797 98-51 4+712243 7990 8211 9303 9241 260815728 -49 77c)15719 (-8912252.7990 317 917 9265110735 917 3265219'79 817 39511(23h 9284 )79 -53 257 73212252 7-90 8211 -303 9243 70815728 -4 -50 '786 -53 -53 1351103 69289 817 337913,)718 <94 X9377994511338993 '5371351510237 9286 717 4137 3+,)511(256 -345110737 -572259 5289 "86 7090 297 7712252 59412252 7990 297 7? 7312252 7990 -5193278t 27512292 7990 -51 ?5P73017292 7990 2572212252 7990 -51 951 299 -35°-12252 79909 141252 7990 -51 6213 9303 9241 8213 9909 9241 8213 9903 9241 8711 9303 9241 8211 9309 9241 8211 9303 92-ti 8211 9303 9241 3213 9312 9241 780615728-1333 0 -44 -4 780815737 780635737-51-49 780835737 -49 -49 -46 -48 780915737 780)815737 -94 -48 780815737 -57 -49 -51 787915737 -53 00 0Ko ? < Ica I 2 3 4 5 6 7 8 9 10 II 12 13 14 App. Fig. 2. Example of a specialized subset of data selected from the master tape described in Figure 1. Millivolt output from the LVDT's stored on card 17 in the master tapes has been converted to stem diameter in millimeters by use of the calibration values recorded each morning. In the data presented here (August 17), card 51 represents the diameter of stems on channels 1, 2, and 5 to 12. Instantaneous net radiation (ly/min) is shown in column 18, while column 14 contains a 15-minute moving average of the radiation given in column 13. Columns 3 and 4 are not used because the corresponding plants (in bin 4) had already been harvested on August 16. Card 52 contains the same information as card 51 except that it is entered into the data stream at 20-minute intervals and contains a 20-minute summary of net radiation in column 13 and a daily total in column 14. 38 ALABAMA AGRICULTURAL EXPERIMENT STATION For many studies, such as those of Huck and Klepper (in preparation) relating stem diameter to plant water potential, it is useful to store data in a format compatible with the Continuous Systems Modeling Program (CSMP) supplied by IBM 1. The values for xylem water potential as a continuous function of time, for example, were computed by a CSMP program described elsewhere (Huck and Klepper, in preparation). Because it views input data as a continuous function, CSMP requires a set of discrete points entered as x-y pairs, with a variable spacing of the x-values permitted. Thus, it is possible to greatly reduce the volume of data without significant reduction of information content, as illustrated in Appendix Figure 3. The linear-interpolation function of CSMP then simply connects each x-y point with a straight line, and a continuous function (of time) which very closely approximates the original data is regenerated in the simulation. The computer-cost of the linear interpolation is generally less than the search time for an input-output operation if the data file had been stored on a peripheral device. To obtain a set of x-y pairs from the dataset shown in Appendix Figure 2, the second derivative (with respect to time) of these rapidly-fluctuating measured variables was computed from a five-point moving average. Each time the second derivative of a time-dependent variable changed, a set of x-y paired values was recorded on a temporary disk dataset, giving both the 3 o00 388,00 392.00 396.00 900.00040.00 HOUR 008.00 12.00 916.00 20.00 28.00 428.00 App. Fig. 3. Instantaneous net radiation plotted as a function of time from August 17 to 19. Values labeled "hour" are cumulative hours from the beginning of August 1972. "X" symbols along the curve represent those points at which the data compression program considered that an entry was necessary because of a significant change in the second time derivative. Negative values of net radiation (night) were ignored. The goodness of fit achieved by straight-line segments connecting the "X" symbols compared with the data line connecting the 720 measurement points per day (2-minute measurement interval) can be seen from visual inspection of the plots. WATER RELATIONS of COTTON 39 time and the value of the variable at that time. The accumulation of data pairs at strategic points was copied to cards for later use in simulation studies, Appendix Figure 4. All net radiation values and stem diameter values for all channels have been processed by a computer program which examines the second deriva- tive of the measured value with respect to time. Card datasets of the compressed data in CSMP-compatible format are also available to interested investigators upon written request to the authors. HOUR Y HOUR 3a3.3, 385.77, 0.228, 955.43, 10.244, 331 43 ,3 17 24 7, 3391 , 1 1, 1).2 1, 391.403,103.251, 31.77, 10.250, 13 .?-1, , 0.4'3 .31)7, 10.376, 343.30, 10.75, 4 3, 4 3,1), 31 1, '77 334.77, 10 . 3 35.77,.10. 153, 3) 9. +3,11. 1-1, .. 3 . 1 3 .J 24, , . 77,310.02?, 400. 10,10.:139, 4 ,'"0 . ' 17o'9,401.41, , .245, .4J<. 77,31 . 155, 7710.195, +74&, -,7.77. 17.70 7 3.:?,10.704, 4'3P.10, 10.20), 4 ,<7 7 ,11.1 . 03, .4 3,31 0. 734, 4 11. 10, 1J.216, 411.77,310.7,1 4 1 2, 7 7,3, 1 2?, 413 . 3. 1"' .2 41 ,. 1 , 1 ?. 22 ,+ 15.10 10.22 , 1(I? 1, 10.2316, 38 4.10.10.2 39 37' .'1, 47, 37.43 ,31(.72331, 137. D33,1 ,(),7J 1 Y HOUR 33:.10, Y 3 HOUR Y ... ... 4110 10 ... A(Js,( 5403 ... 0 1 330 ... AJGC H"101 031.H301 - 312 , 3°2.77, 1) , 91 13.224, 406. ... 73 13H01 ... 5JGCHN453 ... 0)(,CHO73 41 ...AIJCH((\1 . .. ... ... ... ... ... 12,CH ,15.43, 410 417 10<, (7^3, 415*71'0.214, tie-(4, 415.43,37.0E 3, 1.745, 9.t-77, 416, 0 77, .844, Q. 777, 9.072, 9.807, 9.R3!?, 4JU1H\01 41 7,43, 4. 77, .7 ,7, 4.7 5.-3 -,2.--3, 4?8.10. 4:34.37, 437. 77, 43' .13, -27.77, 433.37, 43r.33, AJv., 51 043( 401357 411. .'3 1.5=3, 427.77, ,. 8121, 43"3. "', 7, . 3.7 4, 792 , 41 C.75031 0'1019401 App. Fig. 4. Listing of the X-Y coordinate values of the "X", symbols plotted in Appendix Figure 3. Note that by the information compression technique used here, some 1,440 measurement" points have been sum- marized by approximately 60 points without significant loss of content. The card image records with a . . . symbol. at the end of into a function statement used in listed here are in CSMP-compatible each record for convenience in continuous simulation studies. information format grouping WATER RELATIONS of COTTON 41 W(ATER RELATIOS of COTTON APPENDIX II 4 Data Not Cited in Text and U.S. Weather Bureau Data Appendix Table 1. Summary of plant top measurements made during the 1972 growing season for the cotton plants of bin 2, Auburn rhizotron. Appendix Table 2. Volumetric water content as function of depth and time in bin 2, Auburn rhizotron, 1972. Appendix Table 3. Rooting density as a function of depth and time in bin 2, Auburn rhizotron, 1972. ,Appendix Table 4. Summary of plant top measurements made during the 1972 growing season for the cotton plants of bin 4, Auburn rhizotron. Appendix Table 5. Rooting density as a function of depth and time in bin 4, Auburn rhizotron, 1972. Appendix Table 6. Summary of plant top measurements made during the 1972 growing season for the cotton plants of bin 7, Auburn rhizotron. Appendix Table 7. Volumetric water content as function of depth and time in bin 7, Auburn rhizotron, 1972. Appendix Table 8. Rooting density as a function of depth and time in bin 7, Auburn rhizotron, 1972. Appendix Table 9. Summary of plant top measurements made during the 1972 growing season for the cotton plants of bin 8, Auburn rhizotron. Appendix Table 10. Water balance. Volumetric water content as function of depth and time, water added to surface, and water removed from bottom by suction or by plant use, in bin 8, Auburn rhizotron, 1972. Appendix Table 11. Rooting density as a function of time and depth in bin 8, Auburn rhizotron, 1972. Appendix Table 12. Data of temperature, relative humidity, radiation, and windspeed for the experimental period. Data were obtained from the U.S. Weather Bureau station about 1.5 km from the Auburn rhizotron. APPENDIX TABLE 1. SUMMARY OF PLANT TOP MEASUREMENTS MADE DURING THE PLANTS OF BIN 2, AUBURN RHIZOTRON 1972 GROWING SEASON FOR THE COTTON Duraton ofDaily Duration of icrease Date Heigt nghttme i Duration of Maximum Time Water Time( potential a.m. lier hs diameter shinka ge mm Hr. shrinkage shinkeer srnage measuredp -Bars Hr. potential potential p.m. potential measured Hr. July cm Hr. mm X 10' mm-hr. X< 10 Left plant -Bars 7 8 10 11 12 13 9 36.5 37.8 38.5 9.1 39.8 40.6 42.5 45.0 9.8 11.4 9.8 9.8 9.3 .113 ---- 11.0 8.6 14 15 16 17 18 19J 20 21 22 23 24 25 46.5 48.2 50.6 51.9 53.9 55.3 56.8 59.8 12.2 11.2 8.4 .177 .239 .263 .251 .232 .246 .232 .192 .114 -- 6.0 9.7 9.3 11.1 6.0 4.4 7.6 3.2 2.8 2.8 3.6 6.4 5.2 5.9 1.3 a 1.3 1.8 1.1 2.7W 3.0W 0650 0700 13.0 W 11.OE44 1430 4.3 1.4 0.6 5.7 1415 1425 1354 1835 1409 1358 1416 1409 1411 1402 a a 2.7W 2.0W 0655 0704 0957 9.0W 12.7W 6.7W 11.3 12.1 12.1 9.4 1.2 8.0 r 8.0 10.1 8.2 9.9 10.3 61.5 63.5 26 27 64.5 67.7 69.4 70.8 11.7 10.7 10.6 12.8 15.9 .162 .179 .218 .115 .190 .275 11.9 11.9 10.8 10.8 4.4 8.6 8.4 8.8 13.6 10.4 5.8 6.2 9.3 E 3.7W 3.0 W 2.3W 1.7W 0657 0705 0702 0704 0703 11.7W 12.0 W 16.3W 11.7W 12.3W I- 7.7 6.0 28 29 30 31 71.8 74.8 75.6 76.8 10.4 16.4 .298 .290 .140 -- 5.2 9.7 7.9 12.4 14.0 19.2 3.2 7.6 6.8 16.8 10.4 8.1 7.6 11.9 0.5 m m .3.7 1.4 9.0 1.7W 0.8 W z -I m 4.7 0706 12.0 W z Aug. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Sept. 1 2 3 4 5 cm 78.3 79.3 81.0 82.0 83.4 84.7 86.6 86.8 88.0 89.4 90.0 90.5 91.4 91.5 91.0 91.4 91.8 92.2 92.5 93.0 91.8 92.2 92.2 92.4 92.5 92.5 92.8 92.7 92.6 92.7 92.7 cm 92.6 92.4 92.2 92.0 91.5 Hr. 10.1 8.7 9.8 7.9 9.5 9.0 8.5 8.4 mm ---- Hr. 14.1 mm X 10' 19.2 13.2 10.4 15.6 15.6 21.2 mm-hr. X 10 15.7 7.8 5.3 10.2 8.6 15.2 15.8 10.2 4.9 9.8 11.6 -Bars 2.0 W 2.3 W 2.7 W 2.7 W 3.3W Hr. 0705 0704 0703 0706 0703 0707 0702 0707 0705 0710 0848 0702 -Bars 13.7 W 11.7 W 17.7W 15.3 W 16.3 W 16.7W 19.0W 19.0 W 25.3 W 28.7 W 31.3 W Hr. eI 0 .102 .198 .239 11.2 11.0 11.9 1403 3I- .235 .207 11.3 12.2 .175 .121 - 1414 1404 1404 12.9 10.4 9.4 22.4 15.2 8.8 14.8 16.0 20.4 15.6 z 7-I 0 0 10.7 10.6 7.6 6.6 5.0 2.8 6.8 6.9 8.5 6.6 6.6 6.8 6.0 0.0 .179 .138 .118 .084 .168 -.060 -.057 -.029 -. 019 -.002 -. 001 .051 -. 040 12.6 13.2 12.6 11.7 24.0 24.0 4.0 W 6.3 W 5.0W 10.7 E 13.3 E 20.7 W 14.0E 1402 1410 1400 1410 1406 1410 0 24.0 24.0 24.0 24.0 24.0 24.0 0.0 0.0 -.027 .051 24.0 24.0 28.8 34.4 41.6. 27.2 32.0 24.0 28.4 32.8 34.0 37.2 14.3 8.2 27.8 36.8 41.8 29.6 32.7 24.3 33.9 z 7-I 3-I 35.0 39.8 0.0 Hr. 0.0 mm Hr. -----------mm X 102 mm-hr. X 10 31.6- 22.0 W -Bars 26.E 0700 Hr. 37.0 W -Bars 36.7 W 0707 0710 1410 Hr. 1405 32.7 E 36.0 W 1402 (Continued) w APPENDIX TABLE 1 (Con't.) SUMMARY OF PLANT ToP MEASUREMENTS MADE DURING THE 1972 GROWING SEASON FOR THE COTTON PLANTS OF BIN 2, AUBURN RHIZOTRON Duration of Dt Hegtngtieincr~ease DBashrinkagtalnam.totential July cm Hr. mm lnaphsdimeter 9.9 9.2 9.6 9.9 9.3 10.1 9.0 ---- Daily Duration o Maximum srnae mm X TmeTimeT dim- shnkge Hr. shrinkage 10' mm-hr. X 10 potential pieaopasedathrnkatr otnilptnilp.m. a.m. p Water (am.) Hr. Tim Water measured Tie(m. potential maured ma -Bars -Bars Hr. Right plant 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 35.5 35.8 36.0 37.0 38.3 40.5 41.5 43.0 44.6 46.8 47.8 49.9 51.6 54.2 56.5 57.0 59.7 61.7 64.7 65.4 68.0 70.5 71.8 73.2 74.3 12.6 .108 .167 .212 .243 .250 .393 .314 .323 - 9.3 8.6 9.0 7.7 12.2 7.9 9.4 11.3 10.8 11.0 12.6 13.0 5.3 10.4 9.6 6.0 2.4 2.8 2.0 7.2 4.0 7.2 7.2 10.0 16.8 27.8 26.0 4.5 3.0 0.9 1.4 0.6 5.7 1.6 3.8 4.4 6.9 8.6 22.1 18.2 1.8 7.9 I 2.3W 0715 0737 a 0W 2.3W 4.3 W 071 12.0 E -14.0- 1447 0714 9.0 9.0 9.9 10.1 11.0 8.4 9.0 11.4 1430 1445 5.3W 2.3W W 79.0W 1.3 0916 0735 0738 n C I C 12.3 W 1438 1452 1443 .198 .169 .317 .426 1.7 W x z 8.8 16.0 1.7 E 0742 12.0 W 1451 1708 1402 z Aug. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Sept. 1 2 3 4 5 cm 75.6 77.4 78.5 80.5 83.5 83.7 86.0 87.5 89.5 90.2 91.0 91.7 92.9 92.5 93.6 94.2 94.3 94.4 94.6 95.0 94.2 94.5 94.2 94.6 95.0 95.3 95.1 95.1 95.2 94.9 cm 94.6 94.5 94.5 94.5 94.5 Hr. 9.8 7.3 8.7 8.5 8.7 9.0 9.3 7.0 10.3 8.2 7.3 7.7 8.7 3.8 6.6 4.9 6.5 8.7 6.6 6.2 5.4 0.0 0.0 0.0 0.0 mm Hr. 17.3 11.0 11.5 12.4 11.6 14.1 13.5 13.0 10.5 11.6 11.8 12.2 16.1 15.5 19.9 24.0 mm X 10' 21.2 9.6 10.8 15.6 15.6 25.2 23.6 21.6 12.0 11.6 16.8 18.0 29.6 21.2 31.2 41.2 56.0 38.8 44.0 36.0 42.4 41.2 44.4 46.4 44.8 35.2 mm-hr. X 10 21.2 5.2 6.9 11.4 9.1 18.2 15.3 15.5 6.4 8.4 9.6 11.8 21.6 11.0 _24.0 39.9 55.0 41.2 46.2 37.7 47.2 43.0 45.6 50.9 -Bars 3.3E 4.0E 3.3 E 3.3-W 3.0W 4.3 W 5.7 W 4.7 E 5.0W Hr. 0816 0755 0743 0737 .006 .211 .180 .162 .157 .083 .060 .188 .174 .151 .111 .076 .046 -. 080 -. 048 -. 017 -. 001 -. -Bars 7.7E 5.0 E 13.3 W 12.3 W 16.0 W Hr. 1752 1830 1450 1439 1448 1435 1427 1444 1438 1428 1437 1431 1435 m m 0737 0742 0750 0745 0735 0735 0740 09201 0730 17.3W 15.0 W 13.3 W 20.3 W 21.7 W 25.3 W 29.3 W 31.0 W 0 O 0 -. 037 .015 24.01 24.0 24.0 24.0 24.0 12.7 E 11.7 E 25.3 E 11.7 E 22.7W -Bars 28.0W 045 -. 014 +.005 -. 060 24.0 24.0 23.7 24.0 ---37.0W -Bars 36.0W Hr. mm Hr. mm X 10' --mm-hr. X 10 0729 Hr. 0734 1435 Hr. 1432 E ast ------ - -- -- ------ --- 32.0E 0735 36.7W 1428 U' 46 ALABAMA AGRICULTURAL EXPERIMENT STATION 46 APPENDIX TABLE 2. ALABAMA AGRICULTURLEPRMN TTO VOLUMETRIC WATER CONTENT AS FUNCTION OF DEPTH AND TIME IN BIN 2, AUBURN RHIZOTRON, 1972 Depth 80 July 60 .198 .180 .166 .155 .141 .132 .123 .110 .102 .0915 .085 .079 .074 .067 90 cm3 /cm 120 3 150 .212 .. 08 2 .208 .208 .210 .212 .215 180 .251 .262 .266 .266 .803 .308 .326 .837 Total water use cm/day .81 .78 .37 .36 .42 .16 .38 1.21 .62 .54 .65 1.1 10 12 14 17 19 21 24 26 28 81 Aug. 2 4 7 9 11 14 16 18 21 28 25 27 8.0 Sept. 1 ~ v 5 8 .216 .200 .177 .158 .138 .126 .118 .107 .100 .094 .084 .078 .074 .067 .187 .177 .167 .158 .147 .140 .132 .120 .113 .105 .094 .086 .078 .067 .215 .201 .195 .190 .183 .178 .172 .164 .157 .138 .130 .123 .107 .148 .212 .207 .199 .295 .187 .295 .297 .180 .172 .260 .251 .213 .063 .059 .055 .053 .063 .059 OS55 .053 .062 .056 .052 .049 .095 .084 .073 .053 .048 .043 .140 .120 .104 .081 .071 .051 .048 .046 .044 .051 .048 .046 .044 .046 .042 .040 .038 .067 .061 .040 .036 .035 .034 .177 .162 .128 .106 .062 .052 .046 .083 .045 .042 .040 .039 .037r .042 .040 .039 .037 .036 .034 .033 .032 r~I-r .042 .038 .034 .033 .032 .038 .035 .033 .032 .032 .032 1.18 1.29 .84 .85 .72 .72 .70 .38 .29 .24 .16 .08 .06 WATER RELATIONS of COTTON 47 AS A FUNCTION OF DEPTH AND RHIZOTRON, 1972 APPENDIX TABLE 3. ROOTING DENSITY TIME IN BIN 2, AUBURN 30 June 26 28 30 July 3 5 7 10 12 14 17 19 21 24 26 28 31 Aug. 2 4 7 9 11 14 16 18 21 23 25 27 30 Sept. 1 5 .63 .69 .63 .96 .89 .97 1.07 1.20 1.40 1.47 1.60 1.40 1.77 1.77 1.77 1.77 1.82 1.77 1.72 1.60 1.38 1.58 1.53 1.36 1.13 .90 .50 .61 .56 .31 .28 60 .10 .10 .0,9 .23 .24 .27 .45 .56 .64 .77 .89 .87 1.05 1.32 1.30 1.25 1.32 1.42 1.35 1.15 1.05 1.20 1.15 1.10 1.02 .90 .84 .77 .82 .61 .50 Depth 90 0 0 .04 .04 .16 .24 .45 .69 .85 1.00 1.13 1.31 1.53 1:68 1.70 1.83 1.78 2.04 2.02 1.88 1.81 1.81 1.73 1.71 1.71 1.46 1.38 1.36 1.08 1.08 .85 120 0 0 0 0 .07 .16 .24 .34 .45 .53 .61 .66 .81 .89 .94 1.09 1.09 1.31 1.55 1.53 1.53 1.48 1.41 1.43 1.33 1.23 1.25 .95 .87 .87 .36 150 0 0 0 0 0 .07 .13 .19 .24 .29 .37 .35 .51 .56 .72 .85 .87 1.20 1.80 2.05 2.00 2.12 2.02 2.11 1.58 1.51 1.51 1.13 .97 .69 .09 180 0 0 0 0 0 0 .10 .10 .27 .27 .43 .35 .43 .66 .98 1.13 1.21 1.58 1.88 2.38 2.81 2.81 2.53 3.01 2.39 2.10 1.81 .74 0 .10 0 3 cm root/cm soil APPENDIX TABLE 4. SUMMARY OF PLANT ToP MEASUREMENTS MADE DURING THE 1972 GROWING SEASON FOR THE COTTON PLANTS OF BIN 4, AUBURN RHIZOTRON Dae Hegt Daily Duration ofximumWaterDuration shink in ihtie linear phase diameter shikge Duation f shrinkage Timedimee shrink age Time Tie(m. (am.) Water potential potential am. potential potential p.m. measured measured July 7 8 9 10 cm 31.9 Hr. 11.5 mm Hr. ____ 13.7 mm X 102' mm-hr. X 10 Left plant 6.8 -Bars Hr. -Bars Hr. 32.5 32.5 33.1 3.8 2.7 2.0W _ 6.6 12.2 11.0 12.7 ____ 14.4 4.4 9.6 5.2 0655 0703 0657 10.0 W 1435 11 12 13 14 15 16 34.0 35.5 36.5 38.0 39.3 39.7 9.2 1.8 6.3 10.7 9.2 8.7 7.9 9.9 10.6 .025 .173 .132 ---.183 .292 .308 .296 11.0 14.4 5.8 13.0 9.9 9.4 10.5 12.9 2.3 E* 2.3 E 1.7 W ---11.3 B 8.0 6.8 10.8 1.6 4.0 1.0 9.6 0.3 1429 1358 1840 1410 - 17 18 19 20 41.0 41.8 43.0 43.4 0706 0700 11.7 W 6.0W 2.8 3.6 C F- 21 22 23 24 25 26 27 44.5 45.3 46.0 46.3 47.1 47.5 47.7 9.3 9.3 10.7 12.6 10.4 11.0 .160 .165 .160 .097 -. 018 .096 12.1 12.6 14.4 23.6 12.1 20.2 4.8 15.2 9.2 12.4 18.0 33.6 7.6 19.6 8.0 10.4 .037 .102 .183 8.6 --- 20.4 7.2 15.6 12.4 7.4 7.0 12.1 33.7 2.4 16.8 7.0 1.3 10.1 2.0W 2.0W 1.7 W 2.3 W 1.7 W 1.3 W 8.7 W 11.3W 15.3 W 14.7 W 14.0 W 0709 0704 0706 0706 0709 1402 1421 1411 1416 OI ZI m z 28 29 30 31 48.6 48.6 48.7 48.8 -- 6.6 15.5 12.6 Aug. 1 2 3 4 5 6 7 8 9 10 11 cm 49.3 49.1 49.3 49.5 50.0 49.8 50.3 49.8 49.9 49.9 49.9 cm 24.5 25.1 25.5 26.5 28.7 31.4 31.0 31.5 34.6 Hr. 8.7 9.9 8.0 8.4 8.0 8.0 5.0 - - mm ---.061 .097 .080 .028 .049 -. 036 --- Hr. 18.2 13.2 13.7 20.9 17.7 22.6 23.1 --- mm X 10' 15.6 14.0 14.4 21.6 22.8 mm-hr. >X10 12. 0 9. 6 9.0 20. 7 17. 35. 25. -Bars 2.0W 2.7 W Hr. 0710 -Bars Hr. 1418 1407 1417 m m 13.3 W 9.7E 17.7 E 0707 0706 0711 z 0 - ---- 8.2 +.010 21.2 -- 34.4 30.4 33.2 2 2.7 W 5.3W 29..25.3W _ - 6.8 Hr. .029 mm 0708 0 -I 0 July 7 8 9 10 11 12 13 14 Hr. mm X 10' mm-hr. X 10 Right plant r -Bars Hr. -Bars Hr. z L]V' 33.2 12.0OE 1424 15 16 17 18 19 20 21 33.3 34.0 35.3 36.8 38.3 40.0 9.0 __ 9.9 .155 0.8 12.9 11.0 10.1 10.9 11.0 .217 .226 .. 16 2 .129 4.9 10.2 12.4 9.4 6.6 2.0 2.8 3.2 8.8 4.4 0.7 1.3 1.0 1.8 5.4 2.2 (Continued) n0 APPENDIX TABLE 4 (Con't.). SUMMARY OF PLANT ToP MEASUREMENTS MADE DURING THE 1972 GROWING SEASON FOR THE COTTON PLANTS OF BIN 4, AUBURN RHIZOTRON Duration of Daily Duration TimeTime Time Date July 22 Height cm 40.5 nighttime linear phase increase ln of Hr. 11.0 Maximum shrinkage diameter shrinage Water ppotential potmeasuredmeasured (a.m.) Water (p.m.) U- O diametershrinkage Hr. 9.8 12.3 mm .102 mm X 10' 4.8 mm-hr. X 10 2.1----- -Bars Hr. ------------------------- -Bars Hr. 7ala 23 41.1 9.9 9.0 11.0 8.7 .097 .082 10.7 8.4 4.5____ 1.6 12.8 1.9 24 41.0 25 26 27 41.9 43.6 43.7 .091 .069 .119 13.8 9.9 14.6 6.3 10.4 6.6----- 4.8 18.8 9.2 .____ ____ -B-I -------- ----- ---- -------- 28 29 45.3 44.5 45.8 10.6 8.4 .244 --- 22.8 2.7 7.5 28.4 30 12.9 ___ 31 Aug. 1 2 3 4 5 6 7 8 46.0 cm 46.8 48.5 49.1 50.0 51.0 49.7 51.9 51.1 3.2 21.6 mm X 10' 27.9 0.5-----------------8.3 ---Hr. Hr. mm Hr. mm-hr. X 10 -Bars -Bars Hr. C C x m 9 10 11 *West 51.3 51.9 51.3 ** z -l -- - ---- - - --- - -- -- East -I 0 z WATER RELATIONS of COTTON 51 APPENDIX TABLE 5. ROOTING DENSITY AS A FUNCTION OF DEPTH AND TIME IN BIN 4, AUBURN RHIZOTRON, 1972 Depth 15 cm 30 cm 45 cm June 26 28 30 3 July 5 7 10 12 14 17 19 21 24 26 28 31 Aug. 2 4 7 9 11 1.51 1.81 2.46 3.01 3.54 3.74 3.87 3.87 4.18 3.87 3.93 4.12 3.93 4.55 4.37 4.06 3.93 4.61 3.87 3.80 2.31 .11 .11 .11 .19 .27 .27 .59 .59 .51 .51 .59 .66 .59 .59 .59 .59 .59 .59 .59 .59 .51 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 APPENDIX TABLE 6. SUMMARY OF PLANT ToP MEASUREMENTS MADE DURING THE 1972 GROWING SEASON FOR THE COTTON PLANTS IN BIN 7, AUBURN RHZOTRON Duration of nighttime Date Height linear phase increase metershrinkage of DalyDurationWater-(aim.) Daily TimeMaximum diameter TimeimP potel(a.motnt ptnilam oenalsred Waer Waptentarpm shrinkage shrinkage iapm.measured Time potential (p.m.) July 7 cm Hr. 8.5 10.1 10.3 9.0 9.0 mm - Hr. 11.5 mm X 10.8 9.6 10.4 9.2 10.8 mm-hr. X 10 10 ' Left plant 7.4 -Bars Hr. -Bars Hr. 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 29.1 29.5 29.5 31.0 32.0 32.5 34.0 35.5 36.7 37.5 39.5 40.5 43.0 45.3 46.9 48.7 50.5 52.0 54.9 55.6 56.7 59.1 .133 .404 .148 6.1 11.1 10.7 7.4 6.5 r- 3.3 W 3.7 W 3.0 W .188 .107 12.2 6.0 8.2 0705 72 0705 12.0 E 9.3E 9.O 1447 1435 1440 1846 1406 1426 1417 1435 1422 1428 0 .in .in W4 14.3 ---- 9.9 .125 .143 .188 11.2 9.1 9.3 12.8 12.8 3.2 6.4 8.0 13.6 10.4 4.4 13.6 12.4 29.6 12.8 15.6 9.8 7.4 10.6 10.9 11.5 8.8 9.3 11.0 12.2 11.7 10.1 16.1 .125 .170 .043 ---15.4 11.2 12.2 10.5 11.3 5.0 15.4 10.7 8.5 1.5 4.2 5.2 9.2 7.5 3.5 8.4 4.4 16.2 7.6 5.8 3.3 W 9.7 E 2.7 W 2.7 W 2.0 W 0718 1006 0712 0722 6.7 E 11.3 W 12.0 W 12.0 W -I 0 0 -I z 0715 0715 0717 13.7 W 11.7W 13.7W 2.3W 1.3W 30 31 59.0 61.7 61.7 .348 .152 .143 .143 .161 z 1.0W 0719 9.7W 14i12 -- Aug. 1 2 3 4 5 6 7, 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Sept. 1 2 3 4 5 cm 63.9 65.2 66.3 67.5 69.0 70.5 72.5 73.2 75.0 75.9 76.1 76.8 78.0 78.7 78.5 78.3 78.9 79.2 79.6 79.5 80.7 81.2 80.7 81.2 79.8 80.5 79.8 79.8 cm 80.5 80.2 80.3 80.5 80.3 Hr. 11.0 9.8 11.0 .1.2 9.0 9.0 11.0 12.3 9.8 10.6 10.4 10.6 6.6 9.8 8.7 9.3 10.1 11.4 13.3 10.4 9.2 6.0 mm Hr. 11.0 mm X 10' 3.6 9.2 8.8 10.8 19.6 15.2 13.6 16.4 9.2 7.2 16.8 19.2 30.4 18.8 32.8 33.6 31.6 22.8 22.8 31.2 36.0 36.0 36.8 mm-hr. X 10 2.5 6.0 4.2 6.6 12.4 10.6 6.9 106 4.5 4.0 9.6 12.8 21.4 9,6 26.1 31.0 27.8 22.8 24.2 32.4 37.8 28.8 -Bars 1.3W 2.0 W 2.0W 2.7W 2.7 W 3.0W 4.7 E 4.OE 9.7E 11O0E 12.3 W 12.3 E Hr. 0729 0716 0716 0720 0717 0720 0715 0717 0716 0720 0800 -Bars 12.0W 11.3 W 16.0W 14.7 W 14.3 W 9.7W 19.0 W 19.7W 21.3W 20.7 W Hr. 1428 1419 1427 1414 1417 1414 1420 1410 1421 1415 1421 OA -.107 .375 .375 .152 .294 .366 .197 -.241 .233 .151 .107 .072 .063 .018 -. 027 -. 002 -. 027 10.4 9.7 9.6 11.2 11.5 9.9i 10.2 --- -I m m P- z H +0109 9.3 9.3 12.5 12.9 15.9 11.8 21.6 24.0 24.0 24.0 ------ 24.0 -. 009 24.0 -. 027 24.0 -.053 24.0 23.7 ~00 0 A 25.0W ---- 0710 0710 16.7 W Hr. mm Hr. mm X 10' mm-hr. X 10 -Bars 20.0E 29.3 W -Bars 30.7 1419 Hr. 1414 Hr. 0716 W 20.0OE 0719 30.7 W 1409 (Continued) U' APPENDIX TABLE 6 (Con't.). SUMMARY OF PLANT ToP MEASUREMENTS MADE DURING THE 1972 GROWING SEASON FOR THE COTTON PLANTS IN BIN 7, AUBURN RmZOTRON Date Height Duration of linear phase Hr. 8.8 9.3 11.7 10.9 10.1 nighttime iceae mm Daily eDuration of Maximu mdimeter srinagemeasured Time Water potential diamtrshikgisrnaen~kg ametr srinkge ge a.m. potential potential p.m. Hr. -Bars (am) Time Waer ten(pim. measured July 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 cm 31.2 31.4 31.5 31.0 32.0 32.4 34.0 35.8 36.3 38.5 39.5 40.5 42.4 44.3 47.1 48.6 50.0 51.8 53.8 54.8 57.1 59.1 60.9 62.1 63.0 Hr. 16.5 mm X 10' mm-hr. X 10 Right plant 11.6 8.8 7.6 7.2 7.2 9.9 6.2 4.6 5.7 5.4 -Bars Hr. S .067 .103 .062 .116 .113 13.8 10.7 11.6 11.6 -__- 1- 3.0 W 0723 12.7 E 2.7 W ____ 12.2 5.2 7.8 9.6 12.2 12.2 9.3 11.3 0718 0728 0721 0732 0727 0724 13.3 E 15.0 W 13.3W 15.7 W 13.3 W 13.7 W 9.6 10.4 10.9 12.3 9.8 9.2 9.0 10.9 10.4 15.6 12.3 12.5 11.0 18.9 .170 .304 .134 .196 .170 .167 .134 .285 .134 .277 .277 .196 .197 --4.9 11.2 3.6 7.1 8.2 10.0 1.6 7.2 10.0 13.6 16.8 15.2 12.8 13.6 7.2 18.8 3.6 10.0 6.9 0.8 3.5 6.2 9.2 10.4 8.2 4.9 8.0 1.5 12.9 0.4 3.5 3.0 W 3.3 W 2.7W 2.7 W 2.3 W 1.5 W 1418 1432 1427 C m x 1443 1432 1440 m m 0729 0732 z 1.0 w z Aug. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 cm 64.1 65.3 67.0 67.5 68.5 69.9 70.7 72.7 74.0 75.5 76.1 77.9 79.1 80.6 80.6 81.5 82.4 83.4 84.1 84.5 85.1 85.0 85.1 Hr. 10.7 11.2 12.8 12.0 11.2 10.1 9.5 11.0 11.8 9.6 10.1 10.1 11.8 9.0 11.7 4.6 7.4 7.3 7.9 9.9 mm .116 .179 .142 .179 .125 .205 .206 .134 Hr. 11.3 8.3 10.8 10.0 10.2 10.5 10.0 9.1 --- mm X 10' 9.2 6.4 10.0 9.2 12.8 8.4 8.4 6.4 - mm-hr. X<10 6.1 3.0 6.2 6.2 7.0 5.6 5.2 4.2 - -Bars 2.0W 2.3 W 2.3 W 3.0 W 2.7 W 4.7 W 6.3 W 5.0 W 7.0 E 8.OE 12.0 W 12.0 W 16.3 W -Bars 20.3 W Hr. 0740 0729 0725 0727 -Bars 13.0 W 11.3 W 15.3 W 14.0 W Hr. 1439 El 1428 1437 1423 1427 1430 1430 1418 .- I .-0 I 0 0 0730 0741 0732 0727 0724 0730 0810 0718 ---0719 Hr. 0725 10.0 W 14.7 W 18.0 W 16.0 W 85.7 25 26 27 28 85.1 85.3 84.8 ------- 10.6 3.6 5.5 -- .125 .089 .089 .089 .054 .099 .116 .026 .108 .008 -.026 -.026 -.054 -.125 +.027 ---- 9.6 8.3 11.3 11.3 15.1 12.2 13.9 16.7 12.9 22.7 24.0 24.0 24.0 24.0 23.5 --- 7.2 6.4 9.6 9.2 16.0 12.0 17.2 24.8 . 29.2 20.0 32.8 36.8 44.0 51.8 52.7 53.6 4.1 3.5 5.3 5.5 11.4 6.8 11.6 19.8 19.3 16.4 36.9 40.3 50.9 63.8 41.8 --- z 21.3 W 25.3 W - --30.0 W -Bars 32.0 W 1423 1431 29 30 84.9 - -- ----_-- -- 31 ---- Sept. 1 cm 85.1 Hr. _-- mm VIV V ---- -- - 42.4 ---mm-hr. X 10 1429 Hr. 1423 Hr. mm X 10' 4 5 *West 2 3 84.6 84.8 84.9 85.0 --- _ East 0* L Y~ V VV V -V u 20.0OE 0729 32.0W 1417 U' N' 56 APPENDIX TABLE ALABAMA AGRICULTURAL 7. EXPERIMENT STATION VOLUMETRIC WATER CONTENT AS FUNCTION OF DEPTH AND TIME IN BIN 7, AUBURN RHIZOTRON, 1972 Depth 30 8 12 14 17 19 21 24 26 28 31 Aug. 2 4 7 9 11 14 16 18 21 23 25 27 30 Sept. 1 5 July .200 .178 .167 .153 .144 .135 .122 .114 .185 .156 .132 .105 .095 .085 .082 .080 .077 .072 .070 .067 .065 .061 .059 .055 60 .190 .178 .172 .163 .157 .150 .141 .135 ______ 90 .235 .218 .210 .198 .190 .182 .169 .161 .154 .167 .158 .150 .138 .130 .123 .112 .105 .099 .090 .084 .079 .075 .069 .065 .062 120 .229 .222 .218 .210 .205 .200 .191 .185 .180 .172 .165 .159 .147 .139 .131 .119 .109 .101 .087 .080 .073 .067 .059 .055 .049 150 .245 .255 .257 .258 .258 .258 .249 .242 .235 .226 .218 .212 .201 .192 .181 .162 .142 .116 .088 .072 .065 .058 .050 .047 .042 180 .327 .370 .361 .367 .372 .355 .360 .345 .335 .338 .342 .337 .320 .300 .279 .240 .209 .169 .102 .078 .066 .057 .050 .047 .041 Total water use cm/day .04 .56 .38 .36 .72 .50 .78 r cm'/cm .133 .128 .116 .109 .103 .096 .092 .087 .081 .077 .078 .070 .064 .060 .055 .85 .95 .97 .99 .95 1.17 1.37 1.35 .93 .59 .49 .41 .31 .23 WATER RELATIONS of COTTON 37 W(ATER RELATIONS of COTTON APPENDIX TABLE 8. ROOTING DENSITY TIME IN BIN 7, AUBURN AS RHIZoTRoN, 5 A FUNCTION OF DEPTH AND 1972 30 60 June 26 28 30 July 3 5 7 10 12 14 17 19 21 24 26 28 31 Aug. 2 4 7 9 11 14 16 18 21 23 25 27 30 Sept. 1 5 0 0 0 0 .09 .23 .40 .59 .74 .87 .92 .87 1.20 1.30 1.35 1.38 1.43 1.58 1.92 1.90 1.88 1.90 1.75 1.85 1.66 1.60 .90 1.53 1.33 .74 .82 0 0 0 0 0 0 .03 .19 .24 .40 .48 .61 1.02 1.10 1.15 1.20 1.25 1.30 1.53 1.65 1.75 1.80 1.70 1.75 1.73 1.73 1.28 1.58 1.35 1.05 .97 Depth 90 120 cm root/cm3 soil 0 0 0 0 0 0 0 .06 .06 .15 .27 .34 .68 .73 .79 .89 .91 1.17 1.42 1.47 1.49 1.34 1.62 1.41 1.44 1.32 1.10 1.27 1.09 1.02 .71 150 0 180 0 o 0 0 0 0 0 .03 .03 .18 .21 .21 .37 .48 .71 .94 1.17 1.60 2.13 2.38 2.57 2.15 2.54 2.61 2.32 2.30 1.80 2.12 1.51 1.21 .69 0 0 0 0 0 0 0 0 .03 .06 .06 .09 .18 .34 .35 .45 .53 .89 1.15 1.38 1.35 1.45 1.60 1.73 1.60 1.28 1.31 .89 .63 .26 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .11 .27 .43 .74 1.58 1.58 1.73 1.81 1.58 1.66 1.58 .74 .43 .11 0 0 0 U APPENDIX TABLE 9. SUMMARY OF PLANT ToP MEASUREMENTS MADE DURING THE 1972 GROWING SEASON FOR THE COTTON PLANTS OF BIN 8, AUBURN RHIZOTRON Durationof Daily Duration . Date Height linear of nighttime iceae pnase diameter shrinkage Mxmm shrinkage epoter shrinkage Timediamet Time (a.) Waer ten(pim. Waer tal a.m. potential potential p.M.m. oentiald poet measured maue July 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 cm 30.8 31.4 30.0 30.3 32.0 34.4 35.0 36.5 37.7 38.8 39.7 40.2 42.0 43.5 43.8 45.5 46.0 47.0 48.5 49.5 50.9 52.0 53.8 55.3 56.2 Hr. 12.3 11.7 10.7 10.1 9.5 8.8 mm _ .068 .072 .136 .199 .193 .093 Hr. 11.8 9.1 9.4 10.0 9.4 12.7 14.1 mm X 10' mm-hr. X 10 Left plant 10.8 6.0 3.6 2.4 4.4 12.0 9.2 9.0 3.3 2.7 1.7 2.8 5.0 -Bars Hr. -Bars Hr. r- 2.3W 3.0W 0710 0717 11.7W* 1447 1440 X 8.0E** 6.7 W 10.7E 6.7 W 10.7 W 12.0 W 11.3W 9.0W 11.3 W ---- 6.8 2.7 W 2.3W 0706 0721 0715 0727 0718 0720 0721 0723 1445 c 1410 1850 1425 0 m 11.2 13.3 8.8 9.8 8.8 11.2 10.6 11.5 7.7 12.2 11.7 16.1 .142 .197 .232 .169, .170 .188 .151 .268 .125 .188 10.2 9.6 10.4 12.2 10.0 13.0 9.4 10.4 7.8 11.3 .214 --5.6 6.4 10.0 4.8 11.2 6.6 18.4 6.4 5.2 6.4 10.8 3.6 3.7 4.3 2.4 4.9 2.1 7.0 2.2 2.4 2.9 4.3 0.6 3.0W 3.3 W 2.3W 2.0W 0.7 W 0.7 W 1437 1425 1433 m z m z Aug. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 cm 57.2 60.1 61.4 62.5 63.5 64.0 65.9 67.7 69.5 71.0 71.5 73.3 74.5 74.7 74.9 75.4 76.7 77.4 77.6 78.3 79.2 80.2 80.6 80.9 81.3 81.7 81.9 Hr. 10.6 10.7 10.7 11.8 12.2 10.7 9.2 9.6 12.9 10.4 10.1 10.7 mm .178 .233 .196 .179 .169 .152 .098 .125 .160 .654 Hr. 12.1 mm X 10' 8.4 8.0 8.4 10.0 9.2 mm-hr. X 106.1 4.2 4.4 6.1 3.8 10.0 9.4 -Bars 2.3 W 2.0 W 2.7 W 2.3 W 2.7 W Hr. 0733 0721 0720 0723 0722 0732 0724 0720 -Bars 9.7 W 7.7 W 13.0 W 13.3 W 10.0 W 9.0 W 15.7 W :142 Hr. 1432 -. I mo wu - 10.2 11.0 10.2 9.4 11.9 11.9 13.6 14.4 1431 1418 1421 1423 1424 1412 A 0 -I Og O 9.0 8.3 13.3 7.2 6.4 4.4 11.6 6.4 2.5 2.1 8.4 2.2 4.0 W 3.0OE 0 4.3 E 10.7 12.2 10.7 10.4 12.2 11.5 11.8 9.9 7.Hr. 15.0 W 12.0 W 13.3 W 16.7W --- -.072 .062 .036 .053 13.1 .036 .018 .071 -- 10.6 14.0 12.3 19.4 19.3 11.8 - 15.6 6.4 11.6 11.6 12.8 15.6 14.4 8.8 3.4 8.2 7.7 9.7 10.3 7.3 5.O E 8.3E 8.7W 5.0OE 8.3 W -Bars 11.7E 0720' 0723 0804 0712 0713 Hr. 0719 1424 ----- 29 30 31 83.0 ---cm 11.2 Hr. 8.0 mm X 102 4.2 mm-hr. X 10 13.0 W -Bars 16.0W 1422 Hr. 1417 Sept. 1 2 3 4 5 mm 83.3 83.9 84.1 84.1 84.5 12.0E 0722 10.7W 1412 (Continued) APPENDIX TABLE 9 (Con't.). SUMMARY OF PLANT ToP MEASUREMENTS MADE DURING THE 1972 GROWING SEASON FOR THE COTTON PLANTS OF BIN 8, AUBURN RHIZOTRON Duration of 0 Date July Height cm nighttime linar Daily dimeter mm hae m Duration .Time- Time 1110ase of shinkgeshrnkge Maximum diameter shrinkag aemeasured potential Wtr (~. ae a.m. potential potential p.m. Hr. Hr. mm X 10' mm-hr. X 10 maue Hr. oeta poentired -Bars Hr. -Bars Right plant 7 8 9 10 11 12 37.1 38.2 38.5 39.2 40.5 42.0 13 14 15 16 17 18 19 20 21 22 23 24 42.8 44.3 45.4 47.0 48.3 49.2 50.9 52.3 54.5 55.6 8.2 10.7 12.8 13.1 10.7 9.6 10.6 9.8 8.5 ---10.5 .128 .115 .207 .304 .254 .194 8.6 9.7 1.7 11.0 12.7 14.1 8.4 8.4 5.2 0.8 4.8 15.2 14.4 12.4 9.6 8.0 20.0 16.0 13.6 24.4 10.0 3.6 6.9 4.6 -BI- 4.1 0.4 3.4 9.8 2.3 W 0725 14.0E 'a 1506 .3 3.3 W 11.7 9.4 4.6 4.9 0720 0724 1011 0718 0729 c 12.0W 11.0 W 1415 1427 1424 1440 1427 1436 O r C .3m .062 12.2 15.5 14.6 12.2 10.4 9.0 11.6 14.5 11.5 13.9 10.0 13.6 12.9 11.2 18.5 13.4 14.0 13.3 17.0 3.3W 9.3E 4.7 W 4.3W 25 26 27 28 29 30 31 57.3 58.9 60.9 61.5 63.0 64.8 66.0 68.1 68.5 .063 .188 .305 .358 .276 .384 --9.4 13.3 8.5 6.2 13.0 5.0 12.0 W 13.0 W 9.3 W 12.3 W .3 z .3-I 2.7 W 2.0W 1.0 W 0.7 W 0723 0723 0721 m Z .381 .392 .099 .455 .098 3.9 17.7 1.6 7.5 _- 30.4 2.0 12.8 0.8 23.4 4.1 0.2 0726 Aug. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 cm 70.0 71.6 72.3 .73.3 74.8 76.0 77.7 79.0 80.8 81.8 82.9 83.8 84.5 85.9 87.3 88.1 89.1 89.9 91.0 91.7 92.7 93.5 93.6 95.1 Hr. 11.4 13.6 13.1 9.9 13.7 9.3 9.5 9.0 12.9 15.0 10.7 11.7 11.2 10.7 11.0 10.1 9.9 11.5 11.2 12.8 12.8 11.7 mm Hr. 11.3 mm X 10' 7.6 4.8 6.8 4.4 3.6 18.8 5.6 18.4 2.8 2.0 13.6 7.2 21.2 10.4 15.6 15.2 14.8 15.6 15.6 10.4 mm-hr. X 10 4.1 1.8 2.2 3.1 1.0 12.0 2.6 12.1 0.4 0.4 5.9 1.6 14.0 4.9 10.3 10.2 7.8 12.0 12.6 5.3 -Bars 2.3 W 2.0 W 2.7 W 2.0 W 2.3 W 3.0 W 3.3 W 3.7 W 6.7 E 8.7 E 8.3 W 6.7 E Hr. 0740 0725 0723 0726 -Bars 11.3 W 9.3 W 12.3 W 13.3 W 8.7 W Hr. -B-I 1435 1426 1435 1420 1423 1428 0 m m .232 .366 .481 .491 .411 .277 .402 .384 .402 .384 .269 .286 .143 .107 .057 7.7 6.9 7.7 5.5 11.0 7.5 10.4 ---- 3.3 3.0 11.5 8.0 13.9 ---- 9.2 12.5 13.9 12.5 ---- 16.3 ---- 22.2 9.2 m 'V-I z 0 0726 0737 0729 0724 0723 0726 0811 0715 0716 Hr. 0722 0726 n 0 12.3 W 14.0 W 13.3 W 11.7 W 14.0 W 17.3 W ---12.7 W -Bars 15.7 W 11.3W 1428 1415 1426 1421 1427 z .035 25 26 27 28 95.7 95.7 96.1 --- 30 31 Sept. 1 2 3 4 5 *West 29 --12.3 Hr. mm Hr. mm X 102 mm-hr. X 10 ---- 97.0 cm 97.5 98.1 98.1 98.1 98.6 * 8.0 W -Bars 12.0 W 11.7E 1425 Hr. 1420 - East 1415 0. 0%N APPENDIX TABLE 10. WATER BALANCE. VOLUMETRIC WATER CONTENT AS FUNCTION OF DEPTH AND TIME, WATER ADDED TO SURFACE, AND WATER REMOVED FROM BOTRTOM BY SUCTION OR BY PLANT USE IN BIN 8, AUBURN RHIZOTRON, 1972 30 July 8 10 12 14. 17 21 26 28 31 Aug. 2 4 9 11 14 16 18 21 23 25 27 30 Sept. 1 5 LL .262 .226 .197 .175 .172 .187 .247 .227 .201 .177 .325 .387 .275 .170 .212 .172 .126 .143 .229 .227 .185 .228 .255 ;~%.7 60 .274 .260 .260 .237 .223 .222 .234 .225 .196 .195 .270 .222 .250 .196 .187 .173 .138 .150 .198 .214 .198 .200 .218 Depth (cm) 120 90 cm/cm3 150 .327 .319 .311 .295 .287 .293 .265 .270 .256 .262 .255 .239 .237 .230 .228 .220 .195 .190 .2006 .251 .277 .260 .250 iso .367 .337 .337 .315 .325 .317 .292 .293 .288 .285 .272 .260 .274 .252 .268 .260 .245 .239 .232 .306 .337 .334 .281 I _IILC ~~IZI Water Water added removed (Liters) (Liters) Water use period Date Total water use cm/day .230 .235 .221 .213 .190 .191 .176 .177 .167 .162 .161 .160 .174 .156 .145 .128 .132 .165 .181 .178 .174 .166 .262 .257 .261 .235 .218 .222 .200 10 6 4 20 4 4 5 0.5 8-10 10-14 14-17 17-21 21-26 31 Aug. 4 4-9 9-14 14-18 26-31 1.34 1.37 0.57 0.48 0.67 0.60 0.17 0.60 2.14 C a- r .200 .196 .195 .174 .182 .190 .185 a a 40 20 20 40 .176 .171 .154 .160 .174 .198 .210 .204 .192 1.86 3.01 0.61 1.55 2.37 20 60 60 I- 18-23 -- 40 40 20 60 Aug.27 Sept. 1 -- 23-27 m m 1-5 z -a 0 z WATER RELATIONS of COTTON WATE REATINS o COTON63 APPENDIX TABLE 11. ROOTING DENSITY AS A FUNCTION OF TIME AND DEPTH IN COMPARTMENT 8, AUBURN RHIZOTRON, 1972 30 June 26 60 28 30 July 3 5 7 10 12 14 17 19 21 24 26 28 31 Aug. 2 4 7 9 11 14 16 18 21 23 25 27 30 Sept. 1 5 r)l .34 .34 .39 .52 .67 .72 .90 1.13 1.25 1.39 1.51 1.66 2.01 2.08 2.32 2.59 2.49 2.86 3.25 3.35 3.42 3.08 3.16 3.43 3.21 3.09 2.80 3.45 3.05 2.52 2.14 n rt~ 0 0 0 0 0 0 0 .04 .04 .15 .18 .27 .48 .53 .69 1.13 1.08 1.18 1.63 1.88 2.05 1.83 1.78 1.93 2.22 1.92 1.88 2.26 1.92 1.73 1.43 Depth 120 90 cm root/cm 3 soil 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .06 .10 .21 .32 .37 .74 .69 .92 1.53 1.71 2.00 1.90 1.61 2.02 2.15 2.12 1.95 2.45 1.90 1.93 1.05 ~1 .06 .09 .09 .20 .26 .26 .34 .34 .39 .42 .55 .80 .93 1.14 1.01 .83 1.33 1.31 1.41 1.41 1.70 1.59 1.26 1.02 150 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .04 .04 .04 .04 .04 .07 .09 0 .12 .07 .20 .21 .40 .34 .31 .40 180 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .05 .09 .09 .14 PERIOD. APPENDIX TABLE 12. DATA OF TEMPERATURE, RELATIVE HUMIDITY, RADIATION AND WINDSPEED FOR THE EXPERIMENTAL RHIZOTBON DATA WERE OBTAINED FROM THE U.S. WEATHER BUREAU STATION ABOUT 1.5 km FROM THE AUBURN t~ 1 Date 1972 0000 67 66 65 78 Temperature -e 1200 0600 66 66 66 65 80 82 82 (OF) Relative humidity (%) Total windspeed 1800 79 80 78 0000 100 100 100 85 82 95 100 100 100 100 100 100 100 0600 100 100 90 99 100 98 93 100 100 100 100 100 100 100 100 98 100 100 100 100 100 100 100 100 94 1200 180060 53 65 48 44 50 45 84 83 98 72 78 100 66 radiation and direction July 7 8 9 10 11 12 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 13 69 70 75 72 69 71 73 76 72 74 70 74 69 73 68 64 67 69 67 72 72 70 70 72 72 72 69 69 73 72 73 67 66 84 82 86 86 86 84 87 92 92 91 73 85 81 85 75 79 78 79 80 88 84 71 82 86 86 72 82 76 82 75 82 69 71 73 100 98 94 92 100 100 100 100 100 100 100 100 50 43 43 44 46 46 42 52 64 72 58 62 52 58 48 44 42 52 100 66 62 64 100 100 80 Ly/day 585 516 474 582 616 560 583 484 483 212 689 580 602 660 Miles/day E 79 E 54 E 63 E 112 N 86 NE 52 S 75 S 62. S 47 5 43 E 55 E 70 E 85 E 98 E 48 N 47 NW 50 W 65 5 78 5 81 W 84 W 99 5 91 E 54 E 70 C C 46 60 100 74 100 80 100 56 100 100 100 570 542 518 555 325 502 324 489 280 892 412 m x z m z Aug. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Sept. 1 2 3 4 5 69 70 79 70 72 73 70 77 76 68 68 74 71 69 68 70 71 68 71 75 73 71 68 69 70 70 69 71 70 71 72 69 66 66 69 72I I 69 69 68 71 71 69 68 71 70 68 69 69 68 66 67 69 70 69 73 72 80 68 68 68 70 72 71 67 66 68 68 67 63 64 68 71 83 86 84 82 87 70 89 88 88 84 85 83 84 85 88 89 80 81 80 79 82 83 70 89 91 92 82 84 85 87 89 92 90 86 85 86 83 84 86 89 92 76 86 83 83 73 78 80 82 81 84 70 81 84 88 81 79 77 76 79 81 74 82 81 80 81 78 79 82 87 82 72 II 100 100 100 100' 100 100' 100 83. 10,0' 100 100, 98, 100 100 100 100, 100 100 100 89 98 87 92 100 100 100 100 78 84 100' 76 96 86 97 96 100; ~1 100 100 100 100 100 100 100 99 100 100 100 100 100 100 100 100 100 100 100 98 100 99 100 100 100' 94 100 82 100 100 100 100 100 100 100 100 ~~ 68 68 70 88 53 100 52 59 58 60' 56 68 59 66 49 100 76 50 47 42 66 48 50 52 48 39 46 43 56 43 51 46 39 37 40 78 71 60 99 99 70 100 61 90 74 100 92 90 81 87 76 100 84 76 57 80 81 68 78 86 76 94 49 52 66 44 59 50 48 38 64 100 532 541 469 466 580 461 571 509 499 416 528 414 407 463 421 497 323 482 492 474 404 477 335 399 453 402 447 522 415 498 452 476 460 423 390 195 S 57 SW 59 W 50 W 47 N 87 W 44 SW 75 W 58 W 70' S 41 E 63 E 48 N 47 E 56 NE 26 E 84 E 57 N 57 N 81 N 101 E 93 E 90 E 90 E 40 W 62 N 60 N 79 N 133 N 133 mg m -I z 0 0 0 -Z E. 128 E 121 E 94 N 48 NW 46 SW 91 N 56 1.1 66 ALABAMA AGRICULTURAL EXPERIMENT STATION APPENDIX III Publications for Which Research Was Conducted Wholly or Partially in the Auburn Rhizotron 1. Fiscus, Edwin L., and M. G. Huck. 1972. Diurnal fluctuations in soil water potential. Plant Soil 37:197-202. Soil water potentials varied diurnally at all depths in a 188-cm (approximately 6-ft.) profile containing roots of large cotton plants. Thermocouple psychrometer probes were inserted horizontally through holes in the glass wall of a rhizotron compartment, sealed at the glass-soil interface, and monitored at 20-minute intervals. Soil temperature monitored with diodes also varied diurnally. 2. Huck, Morris G. 1975. Root distribution and water uptake patterns. In John K. Marshall [ed.] The belowground ecosystem: A synthesis of plant-associated processes. IBP Symposium, Ft. Collins, Colo., September 5-7, 1973 (In Press). This review-type paper discusses the effects of various soil factors upon root distribution and then the effects of root distribution upon water uptake patterns. The paper discusses some of the results from root observation laboratories (the rhizotrons). It further discusses the manner in which rhizotron data can be combined with data from other types of experiments to simulate root system development as affected by soil environmental conditions. 3. Huck, M. G., Betty Klepper, and H. M. Taylor. 1970. Diurnal variations in root diameter. Plant Physiol. 45:529-530. Time-lapse microphotography indicated that some roots of a 14-week old cotton plant shrank and swelled diurnally in response to soil water conditions and aboveground evaporative demand. Time-lapse photography was through a microscope focused through the glass wall onto a root located in soil immediately behind the wall. The root diameter at maximum shrinkage was about 60% of the early morning diameter. 4. Klepper, Betty, and V. Douglas Browning. 1971. Drought affects growth of cotton stems. Highlights Agr. Res. 18:16. Auburn Univ. Agr. Exp. Sta., Auburn, Ala. Cotton stem diameter was monitored using a linear variable differential transformer (LVDT). Output from the LVDT was recorded at 2-minute intervals on a digital data acquisition system. During a drying cycle, the stems shrank diurnally. The daily increase in diameter slowed as the soil became progressively drier. A rhizotron compartment was covered with sheet metal at the soil surface to cause the drought cycle. 5. Klepper, Betty, V. Douglas Browning, and Howard M. Taylor. 1971. Stem diameter in relation to plant water status. Plant Physiol. 48:683-685. An instrument containing a linear variable differential transformer (LVDT) was constructed to obtain continuous nondestructive measurements of both short-term changes in stem diameter and long-term growth. In cotton plants, stem diameters, leaf water potentials, and leaf relative water content are all closely related to net radiation at the top of a canopy. The WATER RELATIONS of COTTON 67 LVDT output was recorded at 2-minute intervals on the digital data acquisition system of the rhizotron. 6. Klepper, Betty, H. M. Taylor, M. G. Huck, and E. L. Fiscus. 1973. Water relations and growth of cotton in drying soils. Agron. J. 54:307-310. Two 70-day-old cotton plants (Gossypium hirsutum L. 'Auburn 7-683') were subjected to a 26-day drying cycle at the Auburn rhizotron to quantitatively study water relations and growth as the soil dried. Measurements were made of rooting density changes; stem diameter and height increase; and soil water content (neutron meter), soil water potential (thermocouple psychrometer), and plant water potential (pressure chamber). The pattern of cotton plant rooting with depth shifted during drying while those grown simultaneously in a similar profile with moisture maintained did not. 7. Molz, Fred J., Betty Klepper, and V. Douglas Browning. 1973. Radial diffusion of free energy in stem phloem: An experimental study. The rehydration of a water-stressed cotton stem was studied experimentally in a rhizotron compartment and in a growth chamber. The main objective of the experiments was to ascertain if a proposed diffusion theory can describe the dynamics of the rehydration process. Stem shrinkage was induced by allowing the soil root system of cotton plants to dry by evapotranspiration. Tension in the xylem was then released suddenly by severing the stem under distilled degassed water, with the subsequent increase in stem diameter monitored with an LVDT. From the basic data of stem diameter vs time, fractional uptake curves for free energy were computed and compared with predictions derived from theory. The comparisons indicate that the theory is applicable at least to first order. The overall study illustrates the intimate involvement of the xylem and phloem as far as radial water exchange is concerned. 8. Moore, Charles L., Fred J. Molz, and V. Douglas Browning. 1974. Transpirational drying: An aid to the reduction of the sanitary landfill leaching. Proc. 4th Ann. Environ. Eng. Sci. Conf., Louisville, Ky., March 4-5, 1974. In press. Rhizotron bins were used to study root penetration and root growth habit into a 1/2-scale sanitary landfill profile. The leachate from drains at the bottom of the bins was collected, measured, and analyzed. Volumes and concentrations of leachate from vegetated and nonvegetated profiles were compared. 9. Pearson, Robert W. 1974. Significance of rooting pattern to crop production and some problems of root research. In The plant root and its environment. p. 247-270. E. W. Carson, [ed.] The Univ. Press of Virginia. This review article discusses various types of facilities for investigating plant root development. The rhizotron's glass wall with wire grid allows the continuous measurement of root development on a nondestructive basis during an entire growing season. These observations can determine how plant root development changes with soil conditions and plant maturity. 10. Pearson, Robert W., Joel Childs, and Zane F. Lund. 1973. Uniformity of limestone mixing in acid subsoil as a factor in cotton root penetration. Soil Sci. Soc. Amer. Proc. 37:727-731. Cotton (Gossypium hirsutum L.) root growth response to different de- 68 ALABAMA AGRICULTURAL EXPERIMENT STATION grees of mixing limestone in strongly acid subsoil was determined using both short-term radical elongation experiments in plant growth boxes and full growth cycle root extension experiments in the rhizotron. The roots displayed no chemotropic response to limed pathways in acid subsoil. Roots grew best when the entire subsoil mass was mixed with limestone. However, when applied at an adequate rate, even poorly mixed limestone increased rooting depth at least twofold. Both radical elongation rate and final root pattern were closely related to percentage of total subsoil mass limed in the incompletely-mixed treatments, even when the neutralized soil zones were as much as 7.6 cm apart. 11. Stansell, J. R., Betty Klepper, V. Douglas Browning, and H. M. Taylor. 1973. Plant water status in relation to clouds. Agron. J. 65:677-678. Stem diameter and net radiation were recorded on the digital data acquisition system for both cloudy and non-cloudy time periods. A pressure chamber was used to determine plant water status. Clouds caused significant changes in plant water status in a short time period, therefore, care should be taken to sample different treatments under comparable radiation. 12. Stansell, J. R., Betty Klepper, V. Douglas Browning, and H. M. Taylor. 1974. Effect of root pruning on the water relations and growth of cotton. Agron. J. 66:591-592. 13. Taylor, H. M. 1969. The rhizotron at Auburn, Alabama - A plant root observation laboratory. Auburn Univ. Agr. Exp. Sta. Cir. 171. This circular describes the rhizotron and the types of research that scientists can perform using the rhizotron and its associated equipment. 14. Taylor, H. M. 1969. New laboratory gets to the roots. In What's new in research. Crops and Soils 72:20. This article describes the usefulness of the rhizotron in conducting plant root studies. It emphasizes that the glass walls of the rhizotron compartment allow measurements of root penetration on a non-destructive basis. 15. Taylor, H. M., M. G. Huck, Betty Klepper, and Z. F. Lund. 1970. Measurement of soil-grown roots in a rhizotron. Agron. J. 62:807-809. Measurements were made of both shoot and root growth on a corn (Zea mays L.) and a tomato (Lycopersicon esculentum) plant in a rhizotron. Root intensity at the transparent panel was estimated by two methods. It increased during the root growing season for both species, but was always greater for corn. Estimates of root density and total root length were three times greater for corn than for tomatoes at the end of the growing season. Sidewalls and glass panels showed no concentration effect on root growth. 16. Taylor, H. M., and Z. F. Lund. 1970. The root system of corn. 25th Ann. Corn and Sorghum Res. Conf. Proc. 25:175-179. The root system of corn is described for a sandy soil in the rhizotron compartment. During favorable growing seasons, a single corn root produced about 18 miles of roots excluding root hairs. The roots were at the bottom of the 6-ft. compartment 89 days after the corn grains were planted. 17. Taylor, H. M., M. G. Huck, and Betty Klepper. 1971. Root development in relation to soil physical conditions. p. 71-91, in D. I. Hillel, [ed.] Optimizing the soil physical environment. Academic Press, New York. This review-type article presents data collected in the Auburn rhizotron WATER RELATIONS of COTTON 69 where three different soil conditions were evaluated for their effects on cotton root development. The data showed that a high-strength soil pan excluded root development through the pan for about 20 days, and that a clay loam soil allowed cotton plants to grow taller than those on a loamy sand soil - presumably because of the greater quantity of available water in the clay loam soil during a period of low rainfall. The cotton roots reached the bottom of the compartment (188 cm) about 80 days after planting. No differences were found among the three compartments in the time at which the roots reached the bottom. 18. Taylor, H. M. and Betty Klepper. 1971. Water uptake by cotton roots during an irrigation cycle. Australian J. Biol. Sci. 24:858-859. Two-month-old cotton plants growing in a rhizotron compartment filled with loamy fine sand were subjected to an irrigation cycle. Rooting density, soil water content, soil water potential, water extraction per unit length of root, plant height, and leaf water potential were estimated throughout the cycle. The soils dried progressively from top to bottom. Water extraction per unit length of root was greater in wetter soils and decreased exponentially as soil water potential decreased. In general, deep roots were as effective as shallow roots in water extraction. Rooting density was greater in the surface soil at first, but became uniform later. After irrigation, water extraction per unit length of root was about the same at all soil depths. 19. Taylor, H. M. and Betty Klepper. 1973. Rooting density and water extraction patterns for corn (Zea mays L.). Agron. J. 65:965-968. An experiment was conducted to compare water-absorbing efficiency of corn ( Zea mays L.) roots deep in the profile with that of roots near the soil surface. Plants were grown in a rhizotron compartment with rainfall excluded by a metal cover over the soil. Soil water content was determined with a neutron probe; rooting density from measurements of roots on the glass viewing surface of the compartment. Leaf area was calculated by a length-width method and plant height was measured daily. Stomatal aperture was estimated twice daily with a pressure drop promoter. 20. Taylor, H. M. 1972. The rhizotron at Auburn, Alabama: Design and three years' use. Proc. 3rd Intl. Seminar for Hydrology Professors. Purdue Univ., Lafayette, Indiana. June 1971. This article describes the rhizotron located at Auburn, Alabama, provides the criteria used in its design and discusses opportunities for research and the problems that have been encountered in the first 3 years of rhizotron use. 21. Taylor, Howard M. and Betty Klepper. 1974. Water relations of cotton; I. Root growth and water use as related to top growth in soil water content. Agron. J. 66:584-588. Many experiments have evaluated the effects of decreasing soil water contents on top growth and yield of plants, but few experiments have simultaneously evaluated root growth. An experiment was conducted to determine the response of cotton (Gossypium hirsutum L., 'Auburn 623b') roots and tops to decreasing soil water content. Plants were grown in rhizotron compartments with rainfall excluded by metal covers over the soil. Soil profile and irrigation schedule treatments provided different levels of soil and plant water potentials. Soil water content was determined with the 70 ALABAMA AGRICULTURAL EXPERIMENT STATION' neutron meter, rooting density from measurements of roots on the glass viewing surface of each compartment. Plant water potential was determined with a pressure chamber apparatus, and top growth was evaluated by plant height. At the same time that total root length ceased to increase, plant top growth slowed or ceased, and plant water potential near sunrise decreased. Root length ceased to increase when the soil water content of any layer increased to about 0.06 to 0.07 cm 3 /cm 3 , which corresponds to a soil water potential slightly wetter than -1 bar, or a hydraulic conductivity of about 2 x 10 -4 cm/day. Thus, for conditions of this experiment, cotton root growth correlated with decreases both in plant water potential and in soil water content. SServing co1875 I1975 Manind' CO - E~r 0 Alabama's Agricultural Experiment Station System AUBURN UNIVERSITY With an agricultural research unit in every major soil area, Auburn University serves the needs of field crop, livestock, forestry, and horticultural producers in each region in Alabama. Every citizen of the State has a stake in this research program, since any advantage from new and more economical ways of T producing and handling farm products directly benefits the consuming public. Research Unit Identification * 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. Main Agricultural Experiment Station, Auburn. Tennessee Valley Substation, Belle Mina. Sand Mountain Substation, Crossville. North Alabama Horticulture Substation, Cullman. Upper Coastal Plain Substation, Winfield. Forestry Unit, Fayette County. Thorsby Foundation Seed Stocks Farm, Thorsby. Chilton Area Horticulture Substation, Clanton. Forestry Unit, Coosa County. Piedmont Substation, Camp Hill. Plant Breeding Unit, Tallassee. Forestry Unit, Autauga County. Prattville Experiment Field, Prattville. Black Belt Substation, Marion Junction. Tuskegee Experiment Field, Tuskegee. Lower Coastal Plain Substation, Camden. Forestry Unit, Barbour County. Monroeville Experiment Field, Monroeville. Wiregrass Substation, Headland. Brewton Experiment Field, Brewton. Ornamental Horticulture Field Station, Spring Hill. Gulf Coast Substation, Fairhope.