. BULLETIN MARCH 324 1960 POTASSIUM REQU IREM ENTS of Crops on IW' , . ALABAMA SOILS A= b AGRICULTURAL EXPERIMENT STATION UNIVERSITY A AU BU RN ANS "'-- E. V. Smith, Director Auburn, Alabamo e CONTENTS Page SOURCES OF POTASSIUM POTASSIUM REQUIREMENT OF CROPS GENERAL ....IN - --- 4-----4 4 7 RELATION TO SOIL POTASSIUM- RESPONSE TO APPLIED POTASSIUM ------------------------ 8 Continuous Cotton Sidedressing Cotton with Potassium Sodium as a Substitute for Potassium Cotton in Rotation with other Crops Cotton Following Hay Crops Corn, Grain Sorghum, and Oats Annual Legumes Peanuts - - - - - - 8 10 11 14 -16 17 - - - - - - - - - - 19 -20 - 21 - - - - - - - Soybeans for Oil -Alfalfa - - - - - - 22 S e r ice a ...............................................................................2 3 Clover-Grass Mixtures for Permanent Pasture .-------------- 24 DISCUSSION SUMMARY LITERATURE CITED 27 28 2 ....- 9 Cover - Leaves from cotton plants show the varying stages of rust resulting from potassium deficiency. FIRST PRINTING 5M, MARCH 1960 POTASSIUM REQUIREMENTS of Crops on ALABAMA SOILS 1 R. D. ROUSE, Soil Chemist AFTER ALABAMA land was cleared of native vegetation for cultivation, it was soon found that soils required the addition of fer- tilizer for good crop production. Early fertility studies showed the need for phosphorus was greater than for potash. Therefore, fertilizers high in phosphorus in relation to potassium were generally recommended. It has become apparent that years of fertilization with such fertilizers has resulted in a buildup of soil phosphorus on many soils and frequently a depletion of soil potassium. An analysis of 50,000 soil samples sent to the Soil Testing Laboratory from all parts of the State during 1953-58 showed that only 7 per cent of the soils need a fertilizer high in phosphorus and low in potassium, 75 per cent need a fertilizer with equal amounts of phosphorus and potassium, and 18 per cent need a fertilizer low in phosphorus and high in potassium. Therefore, no one fertilizer can be generally recommended to meet the needs of all soils. Land that has not been fertilized to any extent still needs a fertilizer relatively high in phosphorus. Land that has been cropped and fertilized may need a fertilizer with any one of three ratios of phosphorus to potassium. The purpose of this report is (1) to summarize results of potassium research conducted by the Auburn Agricultural Experiment Station, (2) to give crop responses to applied potassium, and (3) to relate these responses to soil test values. This infor1 The data reported are from field and laboratory investigations by the Agricultural Experiment Station of Auburn University extending over a period of 30 years. The experiments were conducted by members of the department of agronomy and soils working cooperatively with superintendents of the substations and experiment fields and farmers. 4 ALABAMA AGRICULTURAL EXPERIMENT STATION mation is intended to provide farmers and agricultural workers with a better understanding of potassium needs of various crops when produced under varying conditions of soil fertility and cropping sequences. SOURCES of POTASSIUM Most potassium used in fetilizer is potassium chloride. This applies to mixed fertilizers of various grades and straight potassium materials. However, there are certain exceptions. Potassium used in "tobacco special" is mainly in the form of potassium sulfate. When a source of water-soluble magnesium is needed, as on some soils for potatoes, a form of potassium-magnesium sulfate can be used. There is also a small amount of potassium nitrate on the market. All of these sources of potassium are water-soluble and are readily available to plants. Available sources of commercial potassium are listed below: Commercially Available Sources of Potassium Common name Muriate of potash Sulfate of potash Sulfate of potashmagnesia Sulpomag Nitrate of potash Chemical name and formula Potassium chloride (KC1) Potassium sulfate (KSO4) Potassium-magnesium sulfate (K2SO 4 -MgSO 4) Potassium-magnesium sulfate Potassium nitrate (KNO.) Per cent K0O 60 44 25' 21' 443 1Also contains 8 per cent MgO. ' Also contains SAlso contains 18 per cent MgO. 12 per cent N. POTASSIUM REQUIREMENTS of CROPS General The amount of potassium needed to prevent low crop yields depends on (1) the level of available potassium in the soil, (2) the plant species and yield level, (3) the efficiency with which the plant can obtain potassium from the soil, and (4) the level of other plant nutrients. The effect of increasing amounts of available potassium in the soil on yield of cotton on Hartsells fine sandy loam at the Sand Mountain Substation is shown in Figure 1. These various levels of soil potassium have developed as a result of 18 years of differential potassium treatment. It is evident that smaller amounts of POTASSIUM REQUIREMENTS 5 Yield Seed Cotton ,Ib./A. 2000 1600- 1200- 800- 400- 0 50 100 150o 200 Potassium by Soil Test (Ib.K 2 0/A.) FIGURE 1. Relation between soil test potassium and cotton yield on Hartsells fine sandy loam-Sand Mountain 1952. applied potassium are required for maximum yields as the level of soil potassium increases. A comparison between annual lespedeza and alfalfa shows the effect of crop species and yield expected. Annual lespedeza will make maximum yield when dry matter has a potassium content of 1 per cent, whereas a dry matter content of at least 2 per cent potassium would be required for maximum yield of alfalfa. Where other factors permit a yield of 2 tons of lespedeza hay, the equivalent of about 50 pounds of K20 would be removed; under the same condition, 4 tons of alfalfa would be produced and the equivalent of 200 pounds of K20 removed. Peanuts and cotton offer a good comparison of crops having different efficiencies for obtaining potassium from the soil. In a 2-year rotation experiment of cotton and peanuts at the Wiregrass Substation on Norfolk fine sandy loam, cotton yields were 6 ALABAMA AGRICULTURAL EXPERIMENT STATION increased from 132 to 1,250 pounds of seed cotton per acre by an application of 156 pounds of K20 (60 to peanuts and 96 to cotton). Peanuts showed no increase in yield. Thus, peanuts can obtain sufficient potassium at a soil level extremely deficient for cotton. The importance of balancing the supply of available plant nutrients was pointed out by Rogers (3). He reported results showing that lime increased or decreased yields of cotton and corn depending on the amount of potassium applied and the soil level of available potassium. Some crops do not produce maximum yields when most of the potassium needs comes from fertilizer applied in the drill that season. Therefore, potassium should be applied for the Lb. Seed Cotton 0 32 64 96 Lb. K 0 Applied 2 FIGURE 2. Effect of potassium fertilizer on yield of seed cotton at 3 different soil levels of soil potassium on Kalmia sl, Brewton Field 1957-58. POTASSIUM REQUIREMENTS 7 purpose of building or maintaining the potassium reserves in the soil in addition to producing a good yield. Data from the cotton experiment shown in Figure 1 are an example. When the experiment was begun, the soil potassium level was medium. Forty-eight pounds of' K20 applied annually to cotton for 18 years maintained this level and gave maximum yields. However, where less than 36 pounds of K20 was applied the soil level decreased to low. On plots that began receiving 48 pounds of K20 after the soil potassium level had been cropped to a low value, the application had to be repeated for 5 or 6 years before the soil potassium content was back to medium and sufficient to produce maximum yields (4). During the first 4 years, yields on the depleted soil were only 70, to 80 per cent of maximum. The fifth year the yield was 90 per cent, the sixth year maximum, and the soil level was up to medium. Similar results were obtained in an experiment on Kalmia sandy loam at the Brewton Field, Figure 2. In this experiment rates of potassium were applied at 2 residual levels. On soil testing low the highest yield was only 85 per cent of that made on soil testing medium. This emphasizes that (1) yield is dependent upon total available supply, not just that applied as fertilizer and (2) a rate of potassium adequate to maintain yields over a long period may not be adequate for a depleted soil. In Relation to Soil Potassium Potassium occurs in the soil in several forms: (1) It may be a part of the crystal of primary minerals, (2) it may be a part of the crystal of certain secondary or clay minerals, or (3) it may be held on the surfaces of the very fine organic or clay particles. Since the potassium in primary minerals has remained in this form throughout the ages, it is understandable that it is very resistant to weathering and is of negligible value in any one year. It does, however, play a part in the long-time potassium fertility status of the soil. The clay minerals are more subject to change and the potassium in these minerals, though not readily available to plants, is more likely to become available to a crop. Therefore, it has a greater influence on the potassium fertility status of soils. The potassium held on the surface of soil particles is considered available potassium. It can be displaced by leaching with a weak salt or acid solution and, therefore, is referred to as exchangeable. This is the form that correlates best with crop response to added fertilizer and is the 8 ALABAMA AGRICULTURAL EXPERIMENT STATION form that is measured by the Soil Testing Laboratory. Research has been underway for many years on the amount of this form of potassium in relationship to crop responses from added potassium. In 1942, Volk (11) summarized results of nearly 600 fertilizer tests with cotton conducted over the State. These data showed a relationship between soil test potassium and response in yields to added increments of potassium. They also served as a guide for succeeding work by illustrating that differences in soil characteristics should be taken into consideration in making fertilizer recommendations on the basis of soil analysis. When all potassium response data are considered, soils of the State can be divided into 3 general groups for the purpose of calibrating chemical soil tests. (I) Sandy Coastal Plain soils (II) Clay loam Coastal Plain soils, Piedmont soils, Appalachian Plateau soils, grey soils of Limestone Valleys, Highland Rim soils, and lime soils of the Black Belt (III) Red soils of the Limestone Valleys and acid soils of the Black Belt When the soils are thus grouped, ranges of values can be determined that represent low, medium, or high levels of soil potassium. The ranges of available K20 in pounds per acre for the three soil groups according to research information are: Low Medium High Group I less than 75 75-150 more than 150 Group II less than 100 100-200 more than 200 Group III less than 150 150-300 more than 300 These are values obtained from extracting the soil with a weak acid (0.05 N HC1 and 0.025 N H2SO4 ). All available potassium figures reported in this report are in these terms. Most of the data were obtained as exchangable potassium by the standard procedure of leaching with 1 N ammonium acetate, but have been converted to soil test values by multiplying Group II by 0.80 and Group III by 0.75. Group I required no factor. Response To Applied Potassium CoNTINuous COTTON. Many of the early studies were conducted at low levels of nitrogen and/or without adequate boll POTASSIUM REQUIREMENTS 9 weevil control. These conditions did not permit maximum response to potassium (11, 12). However, those studies that included determination of soil potassium are of value in estimating the rates needed to maintain soil potassium.. Table 1 gives TABLE 1. COTTON RELATED TO RATES OF APPLIED POTASSIUM YR. CHANGES IN AVAILABLE SOIL POTASSIUM (10 AV.) WITH RESULTING K2 0 per acre Soil Available To maintain 0 Treatment K20 lb. per acre init. Lb. Decatur 323 (H) clay---Hartsells 72 (L)6 fsl 4----Norfolk 6 fsl ----- 112 (M) Stough s17--- - - 184 (H) 1930-39 except final Lb. 190 (M) 49 (L) 69 (L) iit. Lb. 96 24 48 med. Lb. 48 48 12 24 48 Yield seed cotton per acre 96 Lb. 1,510 1,057 Lb. 1,658 1,328 Lb. 1,576 1,349 Lb. Lb. 1,457 1,390 1,549 1,348 1,463 48 1,190 1,371 1,424 1,409 1,469 722 1,121 1,237 1,373 48 79 (M) 48 Stough 1938-47, 36 lb.. of N and 60 lb. P 2 0 applied to all plots. Weeno potash had been added. Tennessee Valley Substation. 4Sand Mountain Substation. Soil test values of low, medium and high are indicated in parentheses after lb. ' Wiregrass Substation. Aliceville Field. TABLE 2. RESPONSE OF COTTON TO APPLIED POTASSIUMI IN RELATION TO SOIL POTASSIUM (AVERAGE 1954-57)' Treatment K2 0 /a. Decatur cPy Seed cotton per acre Sa Deca- Gree :n- Hart- Kalmiam ag-o Nofoknans16 Di tur villE e sells 8 7 s1 sl s1 fsl cP3 ScO 1 Lolia Lb. 69 (L) [,184 1,850 2,022 Lb. Lb. 184 (M) _1,040 _1,165 1,126 1,130 1,142 Lb. Lb. 154 (M) 1,446 ;1,338 1,568 1,582 1,584 1,561 Lb. 80 (L) 1,576 1,750 1,793 1,886 1,852 1,849 Lb. 46 (L) 754 1,122 1,462 1,517 1,734 1,753 Lb. 34 (L) 394 887 1,095 1,345 1,345 1,417 Lb. Init. 20 avail.- 0 --- 40 --60 ----- 80 --100-- 175 (M) 1,362 1,362 1,376 1,395 1,412 1,155 1,374 167 (H) 1,209 1,186 1,226 1,254 ,2,144 1.203 1,239 2,234 1All treatments received 80 pounds of N and 100 pounds of P 203 except Tennessee Valley where 60 pounds of N was used and Wiregrass where 72 pounds of N was used. The potassium rates on Norfolk were 0, 24, 48, 72, and 96 pounds per acre. Field. 2Alexandria 'Tennessee Prattville Valley Substation. Field. SSand Mountain Substation. Brewton Field. 7 Monroeville °V1iregrass Substation. Upper Coastal Plain Substation. Field. 10 ALABAMA AGRICULTURAL EXPERIMENT STATION results of an experiment with rates of applied potassium to cotton, conducted at 4 locations over a 10-year period. Differences are apparent in soils as to potassium levels, the rate of decrease with cropping, and the annual amounts of potassium needed to maintain yields and soil potassium. However, all plots were maintained at the medium level of soil potassium with an annual rate of 48 pounds of K20 per acre. The results of a current experiment at eight locations, Table 2, show that on soils testing low cotton responded to applications of 60 to 100 pounds of K20, whereas, on those testing medium or high, a response was not obtained to more than 40 pounds. However, by the third year cotton on the low potassium plots even at the medium and high locations were showing potassium deficiency symptoms and will probably show a yield response in another year or two. SIDEDRESSING COTTON WITH POTASSIUM. In studies conducted by Volk (12) prior to, 1940, results showed potassium to be more efficient when applied ahead of or at planting time than when applied as a sidedressing. Recent studies confirm earlier studies, although the advantage of preplanting applications over split applications is not as great as was previously reported, Table 3. The 5-year average yields show only a slight advantage from applying all potassium at planting over split applications. Most of the increase came from the first year of the study when a definite advantage from applying all the potassium at planting was obtained. The data show that a benefit can be expected from sidedressing with additional potassium when inadequate potassium has been applied at planting. TABLE 3. EFFECT OF SPLIT APPLICATION OF POTASH ON COTTON YIELD, KALMIA SL, BREWTON EXPERIMENT FIELD, 1952-56 K20O per acre' At planting Sidedressed Seed cotton per acre 1952 1953 1954 1955 1956 Av. Lb. 0 32 16 64 32 96 32 128 Lb. 0 0 16 0 32 0 64 0 Lb. 866 1,314 1,107 1,544 1,271 1,409 1,316 1,523 Lb. 362 1,199 997 1,188 1,316 1,197 1,163 1,136 Lb. 344 1,204 1,120 1,459 1,505 1,542 1,502 1,587 Lb. 428 1,316 1,460 1,946 1,825 2,089 2,014 2,210 Lb. 880 1,121 1,130 1,523 1,510 1,498 1,559 1,753 Lb. 476 1,231 1,163 1,532 1,485 1,537 1,511 1,632 All plots received 80 lb. of N and P2O5 per acre. -low (52 lb. K20 per acre). Initial available potassium POTASSIUM REQUIREMENTS 11 This is also shown by the following results obtained on Norfolk sandy loam at the Wiregrass Substation: YIELD SEED COTTON PER ACRE (7 YR. Av.) No sideressing Sidedressing (60 lb. K2 O) Lb. 1,208 1,448 This cotton was grown in a 2-year rotation with peanuts on a soil testing low in potassium. The peanuts received 80 pounds of K20 per acre. The cotton received 42 pounds of potassium per acre at planting time. The sidedressing was applied at chopping. SODJUM AS A SUBSTITUTE FOR POTASSIUM. Research has not shown that plants require sodium. It is essential for animals. However, research shows sodium to be a substitute for a part of the potassium needs of some plants. Numerous studies have been conducted to determine the extent to which it can substitute for some of the potassium needs of cotton (7, 10). In general, sodium has been beneficial only at low potassium levels, although some experiments have indicated benefits at near adequate levels of potassium. Results of a recent field study conducted to determine the value of sodium for cotton are shown in Table 4. Sodium did not increase cotton yields consistently, except at the 32-pound per acre rate of potassium. These yields were less than those obtained from 64 pounds of potassium. This is in line with most of the previous work and leads to the conclusion that, when fertilizing for high yields of cotton, no substitution for potassium should be expected from sodium under Alabama field conditions. TABLE 4. RESPONSE OF COTTON TO SODIUM AT THREE RATES OF POTASH, 1952-56' Treatment K20 per acre' 0 32 Na2O per acre' 64 96 Av. Yield seed cotton per acre Lb. Lb. Lb. Lb. Lb. 1,326 1,534 1,633 1,498 Lb. 1,288 1,545 1,591 4 79 0 .......................... 1,312 1,284 1,231 32 -------------------------1,586 1,527 1,582 64 -------------------------1,536 1,657 1,587 96 ------------------------1,632 128 1,475 1.489 1,433 Av. 32, 64, 96 .................. Field. 'Kalmia sl, Brewton Experiment 2 Initial available potassium-low (52 lb. K2O per acre). SInitial available sodium (31 lb. Na 2O per acre). TABLE 5. RESPONSE OF COTTON, WINTER LEGUME AND CORN GROWN IN A 2-YEAR ROTATION TO APPLIED POTASSIUM (Av. 1930-48) Decatur cl Lb. 1,378 88 -6 Treatment Norfolk fsl Lb. Greenville scl Lb. 997 253 16 Kalmia sl Lb. 315 649 318 Magnolia fsl Lb. 778 396 68 Stough sl Lb. 758 448 6 Decatur clay Lb. 926 113 47 Hartsells fsl Lb. 916 693 99 Yield seed cotton per a. without potassium .............. Increase in yield from 45 lb. K20 per rotation___________. Increase in yield from 90 lb. over 45 lb. K20 _-........ Vetch yield green wt. per a. without potassium ................ Increase 45 lb. Increase 90 lb. in yield from K20 per rotation in yield from over 45 lb. K20 1,120 95 -7 10,044 1,550 662 Bu. 11,429 1,694 9 Bu. 42.5 1.3 -0.3 5,981 3,007 161 Bu. 29.7 10.2 1.9 10,824 3,740 711 Bu. 38.1 4.3 0.0 10,067 1,935 557 Bu. 39.0 3.0 -1.0 10,064 1,094 185 Bu. 33.3 0.7 1.3 8,409 3,191 292 Bu. 49.8 4.6 -0.1 12,269 858 124 Bu. 40.2 0.1 -0.4 " M m C c- Yield of corn per a. without potassium Increase 45 lb. Increase 90 lb. in yield from K2 0 per rotation...... in yield fromover 45 lb. K20....... 31.1 0.1 0.2 > - z 0 C m C m TABLE 6. EFFECT OF POTASH APPLICATIONS AND CROPPING TO A 2-YEAR ROTATION OF COTTON-WINTER AVAILABLE SOIL POTASSIUM AND SOIL TEST RATING 1930-50 LEGUME-CORN ON THE z -I CA Treatment per 2-year rotation Original K__________________ After 20 years no K___________ After 20 years 45 lb. K________ After 20 years 90 lb. K.______. Norfolk fsl Lb. 114 (M) 87 (M) 135 (M) 162 (H) Greenville sal Lb. 178 (M) 90 (L) 159 (M) 209 (H) Kalmia sl Lb. 40 (L) 38 (L) 61 (L) 85 (M) Magnolia sl Lb. 161 (H) 78 (M) 141 (M) 218 (H) Stough sl Lb. 184 (H) 87 (M) 151 (H) 243 (H) Decatur clay Lb. 228 (M) 140 (L) 214 (M) 278 (M) Hartsells fsl Lb. 116 (M) 54 (L) 104 (M) 140 (M) Decatur cl Lb. 452 (H) 236 (M) 260,(M) 442 (H) w. 14 COTTON IN ALABAMA AGRICULTURAL EXPERIMENT STATION ROTATION WITH OTHER CROPS. A 2-year rotation of cotton-winter legume-corn, where the winter legume is not grazed, has been in progress at 8 locations in the State since 1930, Table 5. At the beginning of the experiment, available potassium was medium or high at all locations except one. A study of the change in available potassium with treatment over 20 years, Table 6, and yield response of the three crops to potassium shows that this cropping system requires a relatively low rate of potassium (45 pounds of K 20 per 2-year rotation) to maintain soil potassium and yield. Except for Kalmia sandy loam, which has a very sandy subsoil, the available potassium was maintained at a medium or high level by an application of 45 pounds of K20 per 2-year rotation. Only 4 locations showed a response to more than 45 pounds of K20. Other cropping systems require much higher rates. For example, on Norfolk fine sandy loam at the Wiregrass Substation, continuous cotton did not respond to rates higher than 48 pounds of K20 per acre; yet, when cotton was grown in a 2-year rotation with harvested peanuts, at least 96 pounds of K20 were needed for maximum yield of cotton. In this rotation peanuts received 60 pounds of KzO,Table 7. Additional treatments were introduced in this experiment in 1951 to compare methods of correcting extreme potassium deficiency, Table 8. The comparisons are between (1) single broadcast application of 360 pounds of K20 followed by 48 pounds of K20 annually to cotton and (2) 60 pounds of K20 applied as a sidedressing in addition to annual applications of 24, TABLE 7. EFFECT OF INTRODUCING PEANUTS IN ROTATION WITH COTTON ON 1 POTASSIUM NEEDS OF COTTON Continuous cotton Rate of K20 to cotton Yield seed cotton 1930-40 KO 1940 Cotton-peanut rotation No potash to peanuts 60 lb. K2 0 to peanuts Yield seed cotton per a. 1940-50 K2 0 1950 Yield seed cotton per a. 1951-57 KO 1957 Lb. 0 12 24 48 96 1 Lb. 1,190 1,371 1,424 1,463 1,409 Lb. 67 (L) 87 (M) 92 (M) 115 (M) 163 (H) Lb. 204 164 33880 Lb. 36 (L) 82 (L) 42 (L) 50 (L) 82 (M) Lb. 1203 287 518 1,067 1,742 Lb. 28 (L) 46 (L) 46 (L) 54 (L) 92 (M) 708 1,878 Norfolk fine sandy loam, Wiregrass Substation. KOin 1930 was 117 lb. (M). K0 SPeanuts received no potash on this treatment. 0 C TABLE 8. A COMPARISON OF A SINGLE LARGE APPLICATION OF POTASSIUM WITH ANNUAL SIDEDRESSING IN CORRECTING SEVERE POTASSIUM DEFICIENCY ON COTTON IN A 2-YEAR ROTATION OF COTTON AND PEANUTS m C Treatment no. 1940-50 K 20 per acre 1 Soil test 1951-57 1950 1952 1958 1946-50 Yield seed cotton per acre 1951 1957 1951-57 m Lb. 1______________________________ 24 2_____________________________ 24 3______________________________ 48 4._____________________________ 48 54--------------6--------------1 Lb. 482 243 483 963 48 96 Lb. 37 (L) 38 (L) 60 (L) 53 (L) 39 (L) 82 (M) Lb. 88 (M) 49 (L) 62 (L) 59 (L) 41 (L) 68 (L) Lb. 74 (L) 72 (L) 90 (M) 119 (M) Lb. 221 126 282 250 190 618 Lb. 1,177 408 796 951 441 1,378 Lb. 1,499 1,422 1,793 1,949 914 2,001 Lb. 1,460 937 1,266 1,493 661 z -I1 24 96 54 (L) 92 (M) to per acre. Peanuts grown in alternate years. Prior to 1951 they did not receive fertilizer and beginning in 1951 they receivecl 30 lb. P 205 and 60 lb. K2 0 per acre. 2 A single broadcast application of 360 lb. K 0 made in 1951. 2 60 lb. All plots limed in 1951 and 1955. All plots received 36 lb. of N and 60 lb. of P 0 2 5 until 1955 at which time the N .was increased 1,742 '60 lb. K 0 per acre applied as a sidedressing to cotton. 2 4Treatments 5 and 6 are shown for comparison. Treatment 5 received no corrective application; treatment 6 has received 96 lb. of K20 to cotton throughout the period of the test. ova Ui 16 ALABAMA AGRICULTURAL EXPERIMENT STATION 48, and 96 pounds of K20 at planting. The large broadcast application the first year increased yield more than applying as much as 96 pounds under and sidedressing with 60 pounds of K20 annually. However, by the seventh year the high annual rate was superior. The average yields for the period are about the same for the two, treatments. This indicates that, for immediate yield improvement on the extremely potassium-deficient soils, a broadcast application is probably needed. However, to maintain good yields of cotton in rotation with peanuts, large annual applications are required. This is also borne out in the soil test values, since the available potassium has continued to increase with a high annual rate. There has been a slight decrease following the large single application when the annual rate was only 48 pounds of K20. COTTON FOLLOWING HAY CROPS. Severe potassium deficiency has frequently been encountered when cotton is planted after such crops as alfalfa, sericea, or annual lespedeza that received inadequate potassium. Studies have been made on several soils following these crops, and at all locations potassium applications higher than recommended rates were required to prevent potassium deficiency symptoms and to obtain top yields (5). The severity of the deficiency can be determined in advance by a TABLE 9. YIELD OF COTTON AS AFFECTED BY DIFFERENT ON EXTREMELY POTASH DEFICIENT POTASSIUM SOIL TREATMENTS Treatment K20O per acre 1 Yield of seed cotton per acre Numer 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1957 Drill Broadcast 1958 Drill Sidedress 1 1 1 1 1 1957 1958 Lb. 412 1,819 2,400 2,794 1,656 2,203 2,155 2,213 1,934 2,270 1,075 2,270 2,261 2,746 Lb. 0 60 120 240 0 0 0 0 0 0 0 0 0 0 Lb. Lb. 0 60 60 60 60 120 Lb. Lb. 333 1,158 1,589 1,679 347 243 333 225 302 243 158 351 343 288 120 120 60 120 240 2402 60 60 80 60 60 60 60 Soil test low-40 lb. K20 per acre. All treatments received 100 lb. N and 75 lb. P2 0 5 in 1957 and 175 lb. N and 75 lb. P2 0 5 in 1958. 2 P20 5 from Potassium Meta Phosphate 28 per cent K20,. POTASSIUM REQUIREMENTS 17 soil test if it is suspected that insufficient potassium was applied to the hay crop. Research is in progress to determine methods of application that will increase the efficiency of applied potassium. Past studies have shown that, regardless of the method of application, large total amounts must be applied. For example, an experiment on Chesterfield sandy loam at the Main Station showed no advantage from various combinations of broadcast, drill, and sidedressing over high rates applied in the drill, Table 9. CORN, GRAIN SORGHUM, AND OATS. Corn and cotton require about the same amount of potassium to produce satisfactory yields. Neither removes large amounts of potassium unless corn is harvested for silage. However, corn is much more efficient than cotton in obtaining potassium from the soil. Unless the soil is very low in soil potassium, marked responses are not obtained from potassium additions. This is shown by data from experiments conducted at 9 locations for 5 years on areas previously well fertilized, Table 10. Experiments at Aliceville Experiment Field, Sand Mountain Substation, and Gulf Coast Substation were continued for a second 5-year period with no appreciable increases in response, Table 11. Soil test values for potassium were not available for the beginning of the experiment, but were obtained after 10 years of cropping. These data indicate that 20 to 40 pounds of K20 applied annually to continuous corn is sufficient to maintain these soils at a medium potassium level. Therefore, this amount should be adequate for soils not already depleted to a low potassium level. When the soil has been depleted of available potassium, corn yields are increased by applications of potassium. In an experiment on Decatur clay loam at Alexandria Experiment Field, the yield of corn following 2 years of Kobe lespedeza harvested for hay was increased from 33.6 bushels to 45.5 bushels per acre. On Kalmia sandy loam at Brewton Experiment Field following 5 years of sericea lespedeza, the yield of corn was increased from 56.8 bushels to 88.0 bushels per acre by an application of 48 pounds of K20. In contrast, a similar test on Norfolk sandy loam at the Wiregrass Substation showed no response to potassium, Table 12. The Kalmia soil tested low in potassium, whereas the Norfolk soil tested medium. Similar results were obtained in the 2-year rotation experiment, Table 5. 0500 TABLE 10. RESPONSE OF CORN TO APPLICATIONS OF POTASSIUM ON SOIL PREVIOUSLY WELL FERTILIZED (1947-51) Treatment1 K 2 0 per acre Lb. 0______________ ~~IDecatur ci Bu. 55.0 55.0 57.6 54.3 54.3 Stough slsl Bu. 36.9 40.9 41.8 40.1 41.4 Kalmia Bu. 50.2 54.0 55.6 55.3 54.3 Yield of corn per acre Magnolia Greenville Boswell scfsls Bu. Bu. Bu. 52.0 51.0 49.7 51.2 53.2 53.0 Marlboro 3 Hartsells Bu. fsl Bu. Cecil 4 a s1 Bu. 20_______________ 40______________ 60 -------------80-------------1 2 52.2 53.4 53.4 30.4 32.8 31.9 33.3 36.1 57.6 61.1 66.2 63.2 65.7 65.5 69.4 68.3 68.0 69.2 54.5 51.9 45.7 44.9 52.8 r a If-I a 52.8 All treatments received 80 pounds N and P 205 per acre. Tuskegee Field. 3 Gulf Coast Substation. Pidmn Substation. I3-I m 3-I 5-I x z 33O m m 36Z z POTASSIUM REQUIREMENTS 19 TABLE 11. RESPONSE OF CORN TO APPLICATION OF POTASSIUM (SECOND 5-YEARS 1953-57) KO per 2 acre Lb. Corn yield per acre and soil test values' on different soils Marlboro sl Hartsells fsl Stough sl Yield Ru. Value Yield Bu. Value 71(L) Yield Ru. 32.7 34.6 35.9 Value 75(L) 112 (M) 154(H) 0._____________________. 58.7 62 (L) 50.7 20 62.0 86 (M) 53.8 40 67.0 114 (M) 51.2 60 6______________________ 4.0 134 (M) 52.1 80 __ .__ ___ ._______ 66.5 168 (H) 56.0 1 A continuation of the experiment in Table 10. 2 Soil test values 1956 only. ----------------------189(M) 157(H) 170(H) ----------------------- (M) 108 35.2 34.0 237(H) 253(H) Grain sorghum had about the same potassium requirement as corn, Table 12, but oats were slightly less responsive. A number of other studies on various soils of the State show that for all grain crops 20 to 40 pounds of K20 is adequate except where soil potassium has been depleted to a low level or where small grain is to be grazed during the winter. TABLE 12. RESPONSE OF CORN, GRAIN SORGHUM, AND OATS TO POTASSIUM APPLICATION (2-YEAR ROTATION)1 Kalmia sl' K20 4 Norfolk s1 per acre' Lb. Oats G. sorghum Corn Oats C. sorghum Corn (3-yr. av.) (3-yr. av.) (1-yr. av.) (3-yr. av.) (2-yr. av.) (3-yr. Bu. Bu. Bu. Ru. Ru. Ru. 56.8 76.1 88.0 17.1 28.1 33.4 49.2 68.1 80.7 74.8 74.7 73.5 29.4 28.8 30.4 42.8 45.4 49.8 av.) 24 ----------48-------__---1Data 2 0 by Fred Adams, associate soil chemist. Coin received 116 lb. N and 48 lb. P205 per acre. Oats and grain sorghum each received 50 lb. N and 48 lb. P 2 05 per acre. 3Brewton Wiregrass Substation-soil test for K20 Field-soil test for K 2 0 58 lb. per acre (L). 98 lb. per acre (M). ANNUAL LEGUMES. The amount of potassium needed by vanious winter and summer legumes grown alone depends on their productive capacity and potassium content of the plant required for maximum yield. However, the way in which these plants are utilized has the greatest bearing on fertilizer requirements for sustained production. When grown for green manure purposes, they are not potassium depleting. Volk (9) reported that winter legumes actually conserve soil potassium. Results of his studies on 8 soils ranging from sandy loams to, clays showed that a 20 TABLE 13. ALABAMA AGRICULTURAL EXPERIMENT STATION ON RESPONSE IN YIELD PER ACRE OF SEVERAL CROPS TO POTASSIUM NORFOLK SANDY LOAM-MAIN STATION K20 ally Lb. 0 25 50 100 Soil K201 Lb. Peanuts Nuts Lb. Hay Lb. SoyOats forage beans Forage Crai Lb. Bu. Lb. 870 1,025 1,064 1,214 Bu. 50.5 61.9 57.5 64.1 Vetch Cr. Seed White clover cotton clover Lb. 1,539 1,961 2,138 3,005 Lb. 37 522 1,304 2,126 Lb. 400 1,499 1,511 1,869 40 (L) 1,852 60(L) 2,819 70 (L) 2,940 90 (M) 3,333 1These soil test values series of crops. 3,427 1,300 13.5 4,732 2,719 17.7 5,420 3,300 25.9 5,582 3,566 30.3 were maintained as nearly as possible throughout this winter legume after cotton in a 2-year rotation of cotton and corn reduced the leaching losses of potassium applied to cotton and corn by an average of 17 per cent. On some soils the winter legumes resulted in the conservation of as high as 30 per cent of the applied potassium. Data in Table 5 show that in a cotton-winter legume-corn rotation, winter legumes (mainly vetch and crimson clover) respond to a potassium application when the soil is low or medium but not when the soil level is high. However, since the winter legume actually conserves soil potassium, the potassium applied for their production should be credited toward soil buildup and production of the following crop rather than charged to the production of the winter legume. In contrast, if these same crops are removed for hay or silage, they become potassium-depleting and if grazed they would be intermediate, depending on management. The responses of certain plant species to applied and residual potassium are shown in Table 13. These crops were grown in succession on plots that had 4 different levels of soil potassium. These potassium levels resulted from past cropping and differential potassium applications. Potassium was applied to these crops annually at rates indicated to maintain soil potassium at the initial level. These data indicate that all legumes responded to potassium. This response was intermediate with respect to cotton, a very responsive crop, and to oats, the crop in this sequence showing the least response. satisfactory yields with lower levels of available potassium than cotton. However, when peanuts are grown continuously, their potassium requirement can be dePEANUTS. Peanuts produce POTASSIUM REQUIREMENTS 21 CROPPING ON RESPONSE OF DIXIE RUNNER POTASSIUM 1 TABLE 14. EFFECT OF CONTINUOUS PEANUTS TO Treatment' K2 0 per a. Lb. Available K20 per a. 1949 1955 Lb. Lb. Yield per acre 1950 Lb. Nuts-Hay 3,485-6,000 3,621-6,313 3,583-6,031 3,390-6,750 1951 Lb. Nuts-Hay 1,444-2,809 1,800-2,426 1,636-3,188 1,680-3,299 1952 Lb. Nuts-Hay 2,306-4,836 2,900-4,733 2,756-5,728 3,169-6,398 1953 Lb. Nuts-Hay 1,852-3,427 2,819-4,732 2,940-5,420 3,333-5,582 0--------------. 77 48 78 60 25 50---------------- 85 70 88 100.__-------- 98 1 -------.--.---. Norfolk sandy loam, Main Station. 2All plots received 60 lb. P2 05 per acre each year and were limed as needed to maintain pH above 6.0. termined. Data in Table 14 show that on Norfolk sandy loam no response was obtained from potassium in 1950, the first year peanuts were grown on this soil. By 1953, the fourth crop of peanuts, yields of both nuts and vines had decreased where less than 100 pounds of K20 per acre had been applied annually. Similar results were obtained in an experiment at the Wiregrass Substation on soil that had been depleted by continuous cropping with peanuts. The application of 120 pounds of K20 per acre resulted in a yield increase from 762 to 1,948 pounds of nuts per acre the first year the treatment was applied. At both of these locations the soil tested very low in potassium. TABLE 15. EFFECT OF POTASSIUM FERTILIZATION ON SOYBEAN YIELD Treatment 1 K 2 0 per acre Norfolk fsl 19532 Yield of Soybeans per acre Kalmia sl Marlboro sl Norfolk sl 1953-573 1954-57' 19555 Lb. 0 25 50 75 100 Exchangeable K2 0' Bu. 14.1 16.1 15.8 15.9 14.9 83 (M) Bu. 19.6 22.8 26.0 24.0 50 (L) Bu. 33.2 37.8 36.6 35.3 55 (L) Bu. 13.5 17.7 25.9 30.3 40 (L) SAll tests received 100 lb. P20 5 per acre. All tests except location 4 were limed and all except location 2 received 25 lb. of N per acre at planting. 2Lower Coastal Plain Substation. ' Brewton Field. Gulf Coast Substation. SMain Station. o Potassium values for year of test at locations 2 and 5 and in 1956 at locations 3 and 4. ALABAMA AGRICULTURAL EXPERIMENT STATION ivn -'s c'()H Ott. The aliilitx of soyb eatis to ob~tatin potassiumt frot thie soil is lbetxxceti that of pieatiits and~ cottoni. Thex are also intermediate ini thet amnit of potassilo retilix ed ini harx est. licsotlts f romi so\ leat I Irtilits\ 1 )etii(tincts condut cted1 at 17 locationts 01n farmers' fields iln Iackson Com 'vt shiowxed that 76 Sox per cetnt of the fields wxere lowv in pfltassilnni. F kxe of the locationis shoxwing most response5 to treatmuetnt gax c ani ax (ra2e ilicrease of 27 per cent frtom add itioi of 60 potunds( of K *(. The 1 effect of p~otassiu onH so\hean lelds at 4 locatiotns in th e Coastal Plain is shown iniT able 15. The greatest responIses xxere olbtained at Breton and Aubulniri the two wxith the loxxest soil test x aloes for potassiuit. 'v of Alfalfa requir1(s the h igh est rate of potassim ltii atmi Tis is the result of a comiiited legutmie grown iti Alabatma. high proditetix e capacity atnd high pla tit contetnt of potassitt i requtiredl for mnaxinnitittixmeld. Sturklie atid Witlson ( h) rep)ortedl that at least 200) poimds of K2( per acre atnnutallx is oceded to meet the requtiiremn its of alfalfa ont most soils. The fact that some soils of the State produce satisfactorx xields of alfalfa for a nmbitler of xyears xwith stmaller additions h as led to atteti i1 ts to p)rodutce alfalfa xxith loxx- applications of potassiumi. Iti addiA LFA\LFA. .'3 M1 .. f 4j '? ~~2R*" fr .i FIGURE 3. Loss of alfalfa stand as a result of low potassium. Plot in foreground received no potassium, plots on right and in background received 200 lb. K 0 annually. POTASSIUM REQUIREMENTS 23 tion to decreased production and eventual loss of stand, Figure 3, this practice has resulted in severe yield reduction of the crop planted after alfalfa. The effect on cotton was discussed under cotton following hay crop and has been previously reported by the Auburn Station in 1956 (5). SERICEA. Sericea lespedeza is recognized as a crop adapted to the less productive soils of the State. It has a lower potassium requirement than alfalfa and can be grown on some soils for a number of years without showing a response to potassium. However, it is potassium-depleting when removed for hay but less depleting when grazed. Unless adequate potassium applications are made, yields will decline as soil potassium is depleted. A test on Boswell fine sandy loam at the Tuskegee Experiment Field showed that sericea gave a good response to 60 and 120 pounds of K20, Table 16. When cotton was planted on this area, after the test had been discontinued, extreme potassium deficiency was observed where no potassium had been applied to sericea. This was true even though the cotton received a uniform application of 42 pounds of K20 per acre and followed a crop of grain sorghum that was uniformly fertilized at the same rate. Following this and other tests showing that sericea requires potassium for maximum yields and to prevent soil depletion, tests were conducted at 7 locations on soils previously fertilized (soil test values for potassium are not available) to determine potassium response above 60 pounds of K20 per acre annually. No response to rates above 60 pounds was obtained at any location the first 5 years, Table 17. The test was continued for TABLE 16. SERICEA YIELDS WITH DIFFERENT RATES OF PHOSPHORUS AND POTASSIUM 1 P2 0 per acre Lb. 40 40 80 80 1 2 Samples K2 0 per acre Lb. 0 60 60 120 Soil test potassium Hay per acre 1946 1943-46 Lb. Lb. 2,007 2,690 3,294 3,826 L M M H 1,585 2,840 3,710 5,030 Boswell fine sandy loam-Tuskegee Field. taken two years after the experiment was discontinued. The area had been uniformly fertilized and cropped to grain sorghum and cotton. (Available K20 values at time of sampling: 0 K20-98, 60 K 20-168, 120 K20-228. Ratings in table are estimated.) 24 24 ALABAMA AGRICULTURAL EXPERIMENT RESPONSE OF SERICEA LESPEDEZA TO RATES OF POTASSIUM POUNDS K 2 0 PER ACRE STATION ABOVE 60 TABLE 17. K20 per acre 6-Year average-yield per acre-1948-531 Hartsells fsl Decatur ci Lloyd ci Greenville sci Lb. Lb. Lb. 4,902 5,156 5,144 6-Year av.-1948-5319-56 Lb. 5,377 Lb. 6,466 7,115 6,714 60__________________________ 6,025 120__________________________ 6,060 240__________________________ 6,363 5,524 5,060 Magnolia si Kalmia sI Boswell fsl Lb. 6,915 6,977 7,262 Boswell fSl 2 Lb. Lb. 6,648 60_________________________ 120__________________________ 6,684 240__________________________ 6,772 1 2 Lb. 6,548 6,619 6,230 Lb. 7,022 8,153 8,390 Hartsells 1950-55. By 1957 soil test value of plots receiving 60 lb. K20 was 46 lb. /a. K20 (Low). By 1957 soil test value of plots receiving 240 lb. K20 was 249 lb. K20 (High) . a. an additional 3 years on the Boswell soil in view of the difference in response obtained in this test and the one reported in Table 16. The data reported in the last column of Table 17 show that, although there was sufficient potassium in this soil for 60 pounds K2 0 per acre per year to maintain yield for 6 years, when the test was continued for an additional 3 years at least 120 pounds K20 per acre annually was needed to maintain yields. CLOVER-GRASS MIXTURES FOR PERMANENTrPASTURE. Many small plot experiments with various clover-grass mixtures have been conducted to determine the potassium requirements of permanent pasture mixtures. Yield results from such experiments have not alwvays been satisfactory because of difficulty in obtaining and maintaining uniform stands. Results of several satisfactory tests are reported in 19, and 20. The yields reported should be considered only as relative for a location since the number of clippings made varied with location and year. All locations except those on bottom land gave some response to potassium. It has been shown in Alabama (1) as well as a number of other states that, in addition to yield response, potassium additions encourage growth of legumes in the mixture. Without adequate potassium grass growth frequently limits the growth of legumes, Figure 4. This would be expected since studies with individual plant species have shown most legumes to be more sensitive to potassium deficiency than grasses. How- Tables 18, POTASSIUM REQUIREMENTS 25 TABLE 18. RESPONSE OF CLOVER-GRASS MIXTURE TO POTASSIUM ON BLACK BELT SOILS White clover-Dallisgrass yield per acre dry matter per acre Lb. K 20 Sumter clay (1) Loc. 3 Loc. 2 Loc. 1 Lb. Lb. Lb. 2,719 2,574 2,910 3,405 3,267 1,768 2,203 2,806 2,575 Houston clay (2) Lb. 1,982 2,145 2,379 2,656 2,782 Vaiden clay (3) Loc. 2 Loc. 1 Lb. Lb. 4,234 4,327 4,500 4,313 5,314 2,160 2,110 2,276 2,354 Lufkin clay (4) Lb. 4,185 4,664 4,791 0.___________________. 553 30 1,170 60 1,263 90_____________________ 1,030 120 1,420 Data for Sumter location 3, sociate agronomist. (1) Sumter-Loc. 1 Soil test Loc. 2 Soil test Loc. 3 Soil test iment. Vaiden location 2 and Lufkin by E. M. Evans, asK-medium (170 lb./a.) at beginning of experiment. K-medium (180 lb./a.) at beginning of experiment. K-low (57 lb./a.) on no K20 plots at end of exper- (2) Houston Soil test K-medium (170 lb./a.) at beginning of experiment. (3) Vaiden-Loc. 1 Soil test K-high (432 lb./a.) at beginning of experiment. Loc. 2 Soil test K-medium (166 lb./a.) on no K20 plots at end of experiment. (4) Lufkin Soil test K-medium (151 lb./a.) on no K20 plots at end of experiment. ever, both grasses and legumes can be expected to respond to potassium on most Alabama soils especially after a period of cropping. The amount needed to sustain production will depend to a large degree on yield level and method of harvesting. Results of experiments on Norfolk sandy loam at the Wiregrass Substation show the effect of management of pasture crops on potassium requirements, Table 21. All plots were limed according to soil tests and received an annual application of 140 pounds per acre of P2 0 5 and K20. Several rates of nitrogen were applied to Coastal Bermudagrass, common Bermudagrass and TABLE 19. RESPONSE OF CLOVER-GRASS TO POTASSIUM ON PIEDMONT SOILS Ladino clover-Dallisgrass Yield per acre dry matter Yield per acre dry matter Crimson-clover-Bermuda per K20acre Appling gravelly sandy loam (1) Lb. 0 40 Lloyd clay loam (2) Lb. 3,535 3,469 Lb. 3,559 4,108 4,157 60 80 3,643 4,046 5,105 160 Data by E. M. Evans, associate agronomist. (1) Appling soil test-low (46 lb. K2O/a.) on no K20 plots at end of experiment. (2) Lloyd soil test-high (230 lb. K 20/a.) at beginning of experiment. 26 ALABAMA AGRICULTURAL EXPERIMENT STATION I xiii 20. ItF:SPrxL uF CL0 ii Vl-;H~ ix\IXII.HE i -o lurii sic~,i U_ \ COAxx . Wh ite clov er-Dallxit rass yieldl per acre i\ () per acr L b. drix miatter Av . 3 loc. tton lanud 1)1 LI). lsog~oi. fsl LI'. Siixjii han txI fsl' Kalia xil sand Lb. Av. I loc. lp hi( sl 1I) LI'. 0 -) :02,04-i 707 1.57 2 1,405 4,227T 4,851 .3,284 5,48() t, 90 1,856 2,080 2.120 1.-472 2,081 -111 0) 80 160_ ---- - 2,:,)6 1950) DataIby FL M. . ai.ws ixi rciat it, iroiois t. Isogo~rai soil t(ext-loxx (.34 lb./a. K 0) on uo K ) plots At ed ot ixpilliiiii. Stixjiiclanna soil test-lil\ (60) lb./a.) on no K_'0 plots ait (lnd ofi cepiiniucit. Bahiaiorass m' erseeile( in) thte wxinter wxith legumes. Onhe series of plots was grazedi aiid antother clipped. The chan ge in soil potassium ov er the 5-\ ear period show s that it miuch greater depletioni of potassium occurred whenui the crop was clipped anid all foragc flox edt than wxhen gazed. H oxxc r, the potatssium e ditph tionu incr ase d as the rate of niitroreui nicrecastd ucdi eii~ itherI meithod of harve sting. Based on changres ini soil Jpot tssiiin 140 p)ounids of K '( per acre adla sutini.d pirodiictioin of th(ese +,