Soil Fertility Studies with Potatoes inCentral and Northern Alabama
%m. o...

.
r
k
CIRCULAR 200
AUGUST 1972
AGRICULTURAL EXPERIMENT AUBURN UNIVERSITY E. V. Smith, Director Auburn,
STATION Alabama
CONTENTS
Page
EXPERIMENTAL PROCEDURES

4
R ESU LTS              
       
   
 
6
Chilton County              Cullm an County
 
 6 
               
6
7
Sand Mountain Substation, Crossville
D ISC USSIO N                                      

9
S umm a ry                                           1 2
LITERATURE CITED 
13 13
ACKNOW LEDGMENTS 
A P P EN DIX                
                          14
FIRST PRINTING
4M,
AUGUST
1972
Soil Fertility Studies with Potatoes in Central and Northern Alabama
W. A. JOHNSON and C. E. EVANS
1
OTATO PRODUCTION in Alabama prior to 1950 was concentrated in a few counties in the southwestern part of the State, primarily in Baldwin County. During the period of 1931 to 1951 acreage in potatoes in southwestern Alabama varied between 8,000 and 30,000 (7). In 1970 the acreage was approximately 6,000 which is about the same as that now planted in northern Alabama, mainly in the Sand Mountain area. During the 1940's and early 1950's fertilizer recommendations for potatoes ranged from 80 to 105 pounds of N, 66 to 88 pounds of P, and 83 to 116 pounds of K per acre. In seasons when rainfall was heavy immediately after planting, an additional 32 pounds of N was applied as a sidedress (7). Studies conducted by Johnson and Wear in Baldwin County (2) showed equally good potato yields were obtained from either 1,800 pounds of 4107 preplant plus 800 pounds sidedressed 1 month after planting or 1,000 pounds of 41212 preplant plus 400 to 800 pounds of 888 fertilizer per acre sidedressed 1 month after planting. Increases in yields from added magnesium (Mg) were obtained only on the coarsetextured soils low in Mg. Work reported by Ware in 1939 (5) and by Ware and Johnson in 1949 (6) showed that 60 to 90 pounds of N, 66 pounds of P and 50 to 75 pounds of K per acre were usually adequate for good yields
Assistant Professor, Department of Horticulture and Associate Professor, Department of Agronomy and Soils respectively.
of potatoes on most soil types in the State; in some tests small increases in yields were obtained from higher rates depending on fertility of the soil. The objective of this research was to determine the effects of rates of nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) on potato production in central and northern Alabama. EXPERIMENTAL PROCEDURES The experiments were conducted on two fields in Chilton County, three fields in Cullman County, and on the Sand Mountain Substation at Crossville in Dekalb County. At the beginning of these experiments, soil samples were taken at each location and analyzed by the Auburn University Soil Testing Laboratory, Table 1. Treatments used in this study consisted of four rates of N, P, and K. The N rates were 0, 40, 80, and 120 pounds with P held constant at 52 pounds and K at 100 pounds per acre. The P rates were 0, 26, 52, and 78 pounds with N held constant at 80 pounds and K at 100 pounds per acre. The K rates were 0, 50, 100, and 150 pounds with N held constant at 80 pounds and P at 52 pounds per acre. Two additional treatments were added. One treatment was a high rate of fertilizer consisting of 160 pounds of N, 104 of P, and 200 pounds of K per acre (equivalent to 2,000 pounds of 41212 + 80 pounds N). The other treatment included the addition of 20 pounds Mg per acre. The Mg treatment received 80 pounds of N, 52 of P, and 100 pounds of K which was the standard in the rates studied.
TABLE I.
SOIL TEST VALUES FOR DIFFERENT LOCATIONS
Farms or area
Year pH
Soil content' Ca Lb./A. P Lb./A. K Lb./A.
Chilton County
Williams Smith Roden
1959
5.8
1959 5.3
1,030(H)
2,500(H)
146(H)
129(H)
238(H)
113(M)
Burgess Cullman County
1959 1959
1959 1962
6.1 5.1
5.8 5.5
1,400(H) 1,480(H)
468(L)
243(H) 71(M)
154(H) 99(M)
170(M) 144(M)
106(M) 173(M)
Shelton_._....__....... DeKalb County Sand Mountain Substation
'Fertility level: Low (L), Medium (M), and High (H). [4]
Yield~s cwt.
Yields cwt.
Yields cwt.
200 150 00 50
200 I50
: A
100 50
B
100L
50
C
0
40 80 Pounds of N per acre
1200
26 52 Pounds of P per acre
780
50 100 Pounds of K per acre
150
FIG. 1. Yields of No. 1 potatoes from rates of nitrogen, phosphorus, and potassium from average yields of 2 farms in Chilton County.
Y elds cwt.
Yields cwt.
Yields
200 ISO
i,
200 I15C 00 50 A 0 40 80 Pounds of N per acre 120 0 8 26 52 Pounds of P per acre
200 150 100 50 C 78 0 50 Pounds of K per acre
100 50
100
1SO
FIG. 2. Yields of No. 1 potatoes from rates of nitrogen, phosphorus, and potassium from average yields of 3 farms in Cullman County.
rYields cwt
Yields
c
Yields cwt.
200 150
200 150
200 150
100
50 0 40 80 Pounds N per acre of
100
50 120 0 52 26 Pounds of P per acre 78
100
50 0 100 50 Pounds of K per acre 150
FIG. 3. Yields of No. 1 potatoes from rates of nitrogen, phosphorus, and potassium from average yields for 4 years on the Sand Mountain Substation.
[5]
Onehalf of the fertilizer was applied in two bands (both sides of seed pieces) at planting and the other half was sidedressed one month after planting when the rows were hilled. For the Mg treatment all was applied at planting. Plots were four rows wide and the two middle rows were harvested for yield records. Treatments were replicated four times in a randomized block design. Red Pontiac variety was used in these experiments. RESULTS Yield data by location and by years are given in Figures 1, 2, and 3 and Appendix Tables 1, 2, and 3. Since grade No. 1 and total yields are somewhat similar in response, the yields of No. 1 potatoes are given in the figures and are generally discussed. Chilton County Yields from the experiments in Chilton County are given in Figure 1 and Appendix Table 1. Nitrogen and phosphorus increased yields more than K. The lowest yield was made on plots receiving no N, averaging only 37 per cent of the top yield, Figure lA. Nitrogen rate of 80 pounds per acre increased yield 121 hundredweight over no N treatment. Increasing N to 120 pounds did not increase yield above that from 80 pounds per acre. Soils receiving no P produced 61 per cent of the top yield. Phosphorus rates of 52 and 78 pounds per acre, respectively, increased yields 43 and 69 hundredweight over the no P treatment, Figure lB. The yield on soil receiving no fertilizer K was 87 per cent of the top yield. The rate of 100 pounds of K per acre had a yield of 23 hundredweight over the yield from the no K fertilizer rate. The highest yield was with fertilizer applications of 80 pounds of N, 52 pounds of P, and 100 pounds K. (This is equivalent to 80120120 of NP 205K20). When 160 pounds of N, 104 pounds of P, and 200 pounds of K were applied the yield was not increased, treatments 3 and 12. Fertilizer Mg did not affect the yield, possibly indicating that this soil contained an adequate amount. Cullman County Yields from the experimental sites in Cullman County are given in Figure 2 and Appendix Table 2. Yield responses to
[6]
rates of N, P, and K were similar to those in Chilton County except that maximum yields were obtained at the highest rates of NPK in Cullman County. Each 40pound increment of N increased yield up to a maximum yield of 164 hundredweight per acre for 120 pounds of N. Without N, the yield was only 36 per cent of the top yield. The yield without fertilizer P was only 71 per cent of the top yield of 157 hundredweight produced from 78 pounds of P per acre. Applications of 52 and 78 pounds of P per acre increased yields 31 and 47 hundredweight per acre, respectively, over yields from no P treatment. Without fertilizer K, the yield was 82 per cent of the top yield. The top rate of 150 pounds of K increased yield 28 hundredweight over the treatment with no K, Figure 2C. Yield responses to individual rates of N, P, and K could be measured only up to 120 pounds N, 78 pounds P, and 150 pounds K, and these are the yields plotted in Figure 2. The highest yield was obtained from the highest rate of complete fertilizer (equivalent to 160240240 of NP 2 5 K20). Although, it is not known whether the higher yield was caused by the extra N, the extra P, the extra K, or a combination of them, N was most likely responsible. The addition of Mg to the fertilizer did not increase the yield of potatoes in these experiments in Cullman County.
0
Sand Mountain Substation, Crossville
Yield. Yields from this study were obtained over a period of 4 years, 198366, from the same plots and are given in Figure 3 and Appendix Table 3. Average yields for the 4 years showed that only 35 per cent of the maximum yield of No. 1 potatoes was produced without fertilizer N. Yields were increased by each 40pound increment of N up to 120 pounds per acre, the top yield being 171 hundredweight of No. 1 potatoes. Yield was only 56 per cent of the maximum without fertilizer P. Yields were increased by each rate of P up to 52 pounds of P per acre. The yield without fertilizer K was 80 per cent of the top yield with K, 166 hundredweight per acre. Most of the yield increase from applied K was to the first 50 pounds per acre. A higher rate of complete fertilizer (equivalent to 160240240 in terms of NP 2 5K 20) gave a 13hundredweight increase over the highest fertilizer rate (120120120 as NP 20 5K 20) in
0
[7]
TABLE 2. EFFECT OF RATES OF NITROGEN, PHOSPHORUS, AND POTASSIUM ON TOTAL SOLIDS AND SPECIFIC GRAVITY OF POTATOES FROM THE 1966 CnoP,
SAND MOUNTAIN SUBSTATION
Fertilizer per acre1 Total 1 solids Mg K P N Lb. Lb. Lb. Lb. Pct. 1 ........ 0....................... 0 52 100 15.97e2 240 52 100 16.91de 3. 80 52 100 0 17.80bcd 4 120 53 100 18.34abc 5 80 00 100 17.54bed 6................ . 80 26 100 18.49abc 780 78 100 18.01abcd 8 80 52 0 19.16a 9.. .. 80 52 50 18.86ab 10 ......80 52 150 16.98de 11. 80 52 100 20 17.80bcd 12 160 104 200 17.30cd
_.
Specific gravity 1.0695g 1.0740f 1.0769cde 1.0789bc 1.0743ef 1.0776cd 1.0762cdef 1.0828a 1.0808ab 1.0746ef 1.0758def 1.0736f
Onehalf of N, P, K, and all Mg were applied at time of planting and 1/2 of N, P, and K was applied as sidedress 1 month after planting. Rates of 26, 52, 78,
1
and 104 pounds of P per acre, respectively, equivalent to 60, 120, 180, and 240 pounds per acre of P2 0 5. Rates of 50, 100, 150, and 200 pounds of K are, respectively, equivalent to 60, 120, 180, and 240 pounds per acre of K2 0. Mg at 20 pounds is equivalent to 120 pounds per acre of Magnesium sulphate. 2 Figures followed by the same letter do not differ significantly at the .05 level
by Duncan's Multiple Range Test.
the rate treatments. It is not known which fertilizer element caused the yield increase, but it was probably N, as evidenced by the Nresponse curve of Figure 3A. Addition of fertilizer Mg did not increase yield in this experiment on the Sand Mountain Substation. Total Solids and Specific Gravity. In 1966 determinations for total solids and specific gravity were made on the potatoes. Results are given in Table 2. Total solids (dry weight) were increased from 15.97 to 18.34 per cent as rates of N were increased from 0 to 120 pounds per acre. A similar increase in specific gravity, 1.0659 to 1.0789, was obtained with increasing N rates. Total solids were decreased from 19.16 to 16.98 per cent and specific gravity from 1.0828 to 1.0746 as the rates of K were increased from 0 to 150 pounds per acre. At 150 pounds of K per acre, the total solids and specific gravity were significantly below those from 0 to 50 pounds of K. Therefore, potato quality was increased by additional N and decreased by the high rate of K. Rainfall during the year was well distributed throughout the growing period, resulting in the highest yields of the 4 years, in which test was conducted, Table 3 and Appendix Table 3. The distribution of rainfall for 1966 seems to have caused good early
[8]
growth and resulted in plants reaching full maturity and maximum accumulation of solids in the tubers even at high N rates. This probably accounted for the increase in total solids and specific gravity. SoilTest Values. Prior to fertilizer applications in 1966, soil samples were taken from each plot to measure the effect of the 4 previous years of fertilizing on soiltest values. Over the 4year period, there was a decrease in soiltest P where no P fertilizer was applied, but an increase in soiltest P where rates of 78 and 104 pounds of P were applied. There was essentially no change in soiltest P from 26 and 52pound rates of P, Tables 1 and 4. The application of 100 pounds of K per year seemed to maintain the level of K in the soil, but reductions in soiltest K occurred with the high rates of N and P. A decrease in soiltest K resulted from 0 and 50pound rate of K. There was an increase in soiltest K at the 150 and 200pound rates of K.
DISCUSSION Houghland (1) in his study on the importance of P in potato production showed that the need for P was highly critical during the early stage of growth for normal meristem development and rapid vine growth, thus assuring adequate plant development and potentially high yields. In the Alabama work reported here, onehalf of P and K was applied 1 month after planting. Since P fertilizer does not move as readily as N and K into soil from rainfall the sidedressed P may not have been fully available to the crop. Therefore, rates of P reported here might have been more efficiently used if all the P had been applied at time of planting. Applying all P at time of planting is important because potatoes are planted early when the soil temperature is low, therefore, requiring more readily available P for satisfactory early growth. Therefore, because of early planting when soil temperature is low, it is understandable that potato yields can be expected to increase when a readily available form of P is applied to soils even when they have a good supply of residual P. Yields differ from year to year, as shown by the data from Sand Mountain in Appendix Table 3. Yields from the same treatments were lower in 1963 and 1965 than in 1964 and 1966. These differences in yields are possibly attributable to different mois[9]
ture conditions during the growing period. Rainfall during the growing season is given for each year in Table 3. In 1963, there were drought periods of 2 weeks in April, 3 weeks in May, and 2 weeks in June; in 1965, there was a drought period of 7 weeks in April and May with not more than .63 inch of rainfall within any 1week period. The highest yields were obtained in 1966, a year in which no drought periods occurred after midApril. During that year, yields were more than double those produced in the drier years of 1963 and 1965. Therefore, it would appear that supplemental irrigation would be highly beneficial during dry years. Total solids in potatoes are very important, especially for chip production. A grower that, sells potatoes for chip production needs to use fertilizer rates that give the highest total solids per acre. In 1966, the 50pound rate of K produced 4,360 pounds of total solids in the No. 1 grade as compared to 4,270 pounds from 100 pounds of K and 4,060 pounds from the 150 pounds of K. Therefore, the lower fertilizer K rate actually produced more total solids than the higher rates of K. The specific gravity is correlated with total solids; when one is high the other is high. It is possible to increase the total solids and specific gravity of tubers by using a sulfate source of K rather than a chloride source, as was used in this study. Wilcox (8), Lujan and Smith (3) and Timm and Merkle (4) have shown that the source and rate of potash affect specific gravity of potatoes. They found that as the rate of K was increased, a corresponding reduction of specific gravity of tubers occurred, and at the same level of K, the chloride source (KC1) usually lowered specific gravity more than the sulfate source (K 2SO4 ). Results of a study by Yungen, Hunter, and Bond (9) showed that increasing rates of N produced significant decreases in specific gravity of potatoes on 10 of 14 farms. They found that variations in specific gravity appeared to be related to degree of maturity at harvest. In the Alabama work, specific gravity and total solids of potatoes were increased by the higher rates of N. Under certain conditions, increasing the rate of N would not be expected to cause an increase in specific gravity and total solids. However, under conditions such as 1966, with adequate rainfall and rapid plant growth, nitrogen at the higher rates could be more fully utilized by the additional growth during the season, thereby permitting earlier maturity and maximum storage of dry matter in the tubers.
[10]
TABLE 3.
RAINFALL DURING GROWING SEASON, SAND MOUNTAIN SUBSTATION
Inches of rainfall by 1/4 month periods'
April periods 1 4 3 2 1 4 3 Year .00 8.51 .42 .00 .95 .81 .59 S 1963 2.38 1.58 1.02 3.28 5.38 5.24 .51 1964 .00 .59 .38 .00 2.31 4.36 2.90 1965 .77 3.60 1.44 .09 .27 .01 .82 1966 1 Periods represent 1/ of month (7 to 8 days each).
March periods
1
May periods 3 2 .53 .05 .01 .08 .63 .32 2.22 3.73
June periods
July periods
4 1.90 .12 .18 1.11
1 .00 1.15 2.79 1.41
2 .00 .00 1.87 .19
3 5.96 1.00 .26 .68
4 1.47 .00 .34 1.19
1 .43 1.42 1.77 1.42
2 .53 1.73 .14 1.35
TABLE 4.
SOIL TEST PH,
ON
P,
K,
AND MG ON SOIL FERTILITY PLOTS FOR POTATOES
SUBSTATION, 19661
SAND MOUNTAIN
Treat
Fertilizer per acre
2
Soil test results
No.
N Lb.
P Lb. 52 52 52 52 0 26 78 52 52 52 52 104
K Lb. 100 100 100 100 100 100 100 0 50 150 100 200
Mg Lb.
pH 5.3 5.2 5.2 5.1 5.2 5.2 5.1 5.2 5.2 5.1 5.1 5.2
P Lb. 96 99 104 95 47 92 119 103 93 105 102 160
K Lb. 161 153 168 149 169 167 139 116 140 202 148 218
Mg Lb. 28 26 27 27 24 26 23 33 26 24 33 20
1___________ 0 2 _________ 40 3___________ 80 4____________ 120 5___________ 80 6___________ 80 80 7_________. 8............ 80 9 ._________ 80 80 10___....... 11___________. 80 160 12...........
1 SThese
0
20
Soil test samples were taken prior to fertilizer application in 1966. rates of fertilizer were applied to plots beginning in 1962. Therefore, 4 applications of these rates were made prior to soil test.
SUMMARY
Field experiments to study the effects of rates of N, P, and K, and the addition of Mg on production of potatoes were conducted for 1 year at two locations in Chilton County, for 1 year at three locations in Cullman County, and for 4 years at the Sand Mountain Substation in Dekalb County. The results from the experiments on farms in Chilton County indicated that 80 pounds of N, 52 of P and 100 pounds of K per acre were sufficient for best production of potatoes in central Alabama. The experiments in Cullman County and at the Sand Mountain Substation indicated that individual rates of N, P, and K used were not high enough to produce maximum yields in northern Alabama. This is substantiated by the fact that higher yields of potatoes were produced from a higher rate of complete fertilizer containing 160, 104, and 200 pounds of N, P, and K, respectively. Fertilizer Mg at the rate of 20 pounds per acre did not increase yields at any of the test areas. Results obtained at Sand Mountain Substation in 1966 indicate that total solids and specific gravity of potatoes can be increased with increase in rates of N, up to 120 pounds per acre, in years when rainfall is well distributed throughout the growing season so that there is a continuous supply of moisture.
[12]
LITERATURE CITED HOUGHLAND, G. V. C. 1960. The Influence of Phosphorus on the Growth and Physiology of the Potato Plant. Amer. Pot. J. 37:127128. (2) JOHNSON, W. A. AND J. I. WEAR. 1956. Effects of Fertilizer and Use of Magnesium and Minor Elements on Yields and Storage Quality of Potatoes in Baldwin County, Alabama. Amer. Pot. J. 33:103112. (3) LUJAN, LAURO AND ORA SMITH. 1964. Potato Quality XXV. Specific Gravity and after Cooking Darkening of Katahdim Potatoes as Influenced by Fertilizers. Amer. Pot. J. 41:274278.
(1)
(4) TIMM, HERMANS AND F. G. MERKLE.
1963. The Influence of Chlorides
on Yield and Specific Gravity of Potatoes. Amer. Pot. J. 40:18. (5) WARE, L. M. 1939. Fertilizer Requirements of the Potato on Different Soils of Alabama. Amer. Pot. J. 16:259266. _ AND W. A. JOHNSON. 1949. Fertilizer Studies with Vege(6) table Crops on Representative Soils of Alabama. (Ala.) Agr. Exp. Sta. Bull. 269. (7) WHITE, MORRIS. 1952. Early Irish Potato Production Practices in
Southwestern Alabama. (Ala.) Agr. Exp. Sta. Cir. 109.
(8)
E. 1961. Effect of Sulfate and Chloride Sources and Rates of Potassium on Potato Growth and Tuber Quality. Amer. Pot. J. 38:215220. (9) YUNGEN, JOHN A., ALBERT S. HUNTER, AND TURNER H. BOND. 1958. The Influence of Fertilizer Treatments on the Yield, Grade, and Specific Gravity of Potatoes in Eastern Oregon. Amer. Pot. J. 35:386395.
WILCOX, GERALD
ACKNOWLEDGMENTS
Credit for information in this publication is given the Substation Superintendents who supervised the field phase of the studies. Especially recognized are C. C. Carlton, M. H. Hollingsworth, and S. E. Gissendanner. The assistance of L. M. Ware, Professor Emeritus, in planning these experiments is acknowledged.
[13]
APPENDIX
APPENDIX TABLE 1. YIELDS OF POTATOES FROM RATES OF NITROGEN, AND POTASSIUM ON FARMS IN CHILTON COUNTY, 1959 PHOSPHORUS,
Treatment No. No.
No. 1 and total yields per acre Fertilizer per acre Average of MWilliam's farm Burgess farm farms N P K Mgfarms N P K Mg No. 1 Total No. 1 Total No. 1 Total Lb. 100 100 100 100 100 100 100 0 50 150 100 200 Lb. Cwt.
43d' 147ab 173a 156ab 86cd 134bc 154ab 145ab 159ab 142ab 159ab 159ab
Lb. Lb. 1____________ 52 0 40 52 2___________ 3____________ 52 80 120 4____________ 52 80 0 5___________ 6___________ 80 26 7____________ 78 80 80 52 8___________ 80 52 9___________ 52 10_..... 80 80 52 11_.... 12_..... 160 104
Cwt.
Cwt.
Cwt.
Cwt.
Cwt.
0
20
7e 61c 166ab 145cd 198a 185ab 180a 181ab 109bc 133d 180a 171bc 207a 178a 168ab 167bc 171bc 186a 180a 178abc 190ab 187a 194a 180abc
85e 58c 73c 165cd 146ab 166ab 200ab 179a 199a 192a 204ab 169a 135b 160d 110b 188bc 153ab 184a 224a 181a 201a 184bc 156ab 176ab 188bc 165a 187a 160a 188a 196b 181a 210ab 175a 194a 198b 170a
Onehalf of N, P, K, and all Mg were applied at time of planting and 1/2 N, P, and K applied to side 1 month after planting. Rates of 26, 52, 78, and 104 pounds of P are, respectively, equivalent to 60, 120, 180, and 240 pounds per acre of P20 5 . Rates of 50, 100, 150, and 200 pounds of K are, respectively, equivalent to 60, 120, 180, and 240 pounds per acre of K2O. Treatment 8 is equivalent to 1,000 pounds of 81212 grade fertilizer per acre. Mg at 20 pounds is equivalent to 120 pounds per acre of magnesium sulphate. 2 Figures followed by the same letter do not differ significantly at the .05 level by Duncan's Multiple Range Test.
[14]
APPENDIX TABLE 2. YIELDS OF POTATOES FROM RATES OF NITROGEN, PHOSPHORUS, AND POTASSIUM ON FARMS IN CULLMAN COUNTY, 1959
Treatment No.
Fertilizer per acre'
Mg NP K
Lb.
Roden's farm No. 1 Total
No. 1 and total yields per acre Shelton's farm Smith's farm No.1 Total No.1 Total
Average of farms No.1 Total
Lb.
Lb.
Lb.
Cwt.
68d 2
Cwt.
91e
Cwt.
86e
Cwt.
68e
Cwt.
72e
Cwt.
96c 125c 176bc
Cwt.
59f
Cwt.
85g
U( u
153cd 74d lO5ed lO6de 103e 128f 0 162bc l86bcd l04ahcd l38abc lS8bcd l4lbc l67bcd 187ab 213ab l2Oab 153ab l84abc 204ab 164b l9Oab 5____________________ 80 0 100 127c 143d 76cd 98de l27cde 147bc il0de 129ef 6____________________ 80 26 100 131c 156cd 9lbcd l25bcd l4lbcde 163bc l2lcde l48def 7______________________________________ 80 78 100 166bc l84bcd ll2abcd 145ab 192ab 212ab 157b iS0be 880 52 0 133c 153cd 97abcd l26bcd iS0bed 165bc l27cde l48def 9___________________ 80 52 50 l6Obc l8lbcd lO6abed i3labed l36bcde l6lbc lS4bcd lS8cde 10___________________ 80 52 150 176ab l92bcd lilabed 143ab l78abc 203ab 155b 179bc 11____________________ 80 52 100 20 179ab l96abc ll4abc lS7abc lS7bcd 176bc iS0be l7Obcd 12___________________ 160 104 200 215a 236a 134a 162a 222a 244a 190a 207a 1 Onehalf of F, and all Mg were applied at time of planting and 1/2 of N, P, and K was applied to side 1 month after K, planting. Rates of 26, 52, 78, and 104 pounds of P are, respectively, equivalent to 60, 120, 180, and 240 pounds per acre of P20 5. 130c
1 __ 0 0__________________ 52 100 2________________________________52 40 100 3____________________ 80 52 100 4 120 52 100

N,
Rates of 50, 100, 150, and 200 pounds of K are equivalent to 60, 120, 180, and 240 pounds per acre of K20. Treatment 3 is equivalent to 1,000 lb. of 81212 grade fertilizer per acre. Mg at 20 pounds is equivalent to 120 pounds of magnesium sulphate. 2 Figures followed by the same letter do not differ significantly at the .05 level by Duncan's Multiple Range Test.
APPENDIX TABLE 3. YIELDS OF POTATOES FROM RATES OF NITROGEN, PHOSPHORUS, AND POTASSIUM ON SAND MOUNTAIN SUBSTATION, 196366 No. 1 and total yields per acre 1964 1965 1966 4year av. Total No. 1 Total Total No.1 Total No.1 Total Lb. Lb. Lb. Lb. Cwt. Cwt. Cwt. Cwt. Cwt. Cwt. Cwt. Cwt. Cwt. Cwt. 1 100 0 52 30P 47f 86f 10Sf 43d 54e 811 12Sf 60i 82i 2._____________ 40 52 100 79de 104de 145e 163e ll4ab l2Sabc 148e 196e 122g 148f 3 80 52 100 0 94bcd 114bcd 179bc 195bc il0ab l2Sabc 240b 291b 156cd 182d 4100 120 52 115a 137ab 198b 213b 122a 145ab 249b 29Gb 171b 196b 5 100 80 0 74e 88e 139e 153e 68c 82d 90f 12Sf 93h 112g 6 80 26 100 98abc lllbcd l75bcd l9lbcd 93b 113c 2Olcd 246cd 142ef 167e 7 80 78 100 li3ab 138a 196b 213b l30a 152a 228bc 279bc 167bc 196b 8 80 52 0 86ede h10ed 152de l7Ode 119a l4Oab l7lde 219cd lS2fg 160e 9 80 52 50 98abc ll9abcd 185bc 204bc illab 125bc 2Slbc 274bc 156cd 181d 80 52 150 il0ab iS3ab 192bc 2l0bc 124a l4Oab 239b 288b 166bc l9Sbc 11 80 52 100 20 lO0abc l26abc l7Ocd 187cd il5ab iS8ab 215bc 270bc iS0de 180d 12 160 104 200 il0ab lS4ab 222a 243a ll2ab iS3abe 290a 329a 184a 210a 1 Onehalf of N, P, and all Mg were applied at time of planting and / N, P, and K was applied as sidedress 1 month after planting. Rates of 26, 52, 78, and 104 pounds of P are, respectively, equivalent to 60, 120, 180, and 240 pounds per acre of P25 Rates of 50, 100, 150, and 200 pounds of K are, respectively, equivalent to 60, 120, 180, and 240 pounds per acre of K20. Treatment S is equivalent to 1,000 pounds of 81212 grade fertilizer per acre. Mg at 20 pounds is equivalent to 120 pounds per acre of magnesium sulphate. 2Figures followed by the same letter do not differ significantly at the .05 level by Duncan's Multiple Range Test. Treatment Fertilizer per acre
No.
N
P
K
Mgt
1968
No. 1
No. 1
10 
K,