69 - 16,127 CRABTREE, Robert Jewell, 1933EFFECTS OF RATES AND SOURCES OF POTASSIUM ON YIELDS AND MINERAL CONTENT OF POTATOES AND EVALUATION OF POTASSIUM QUANTITY-INTENSITY RELATIONSHIPS OF SELECTED MICHIGAN SOILS. University Microfilms, Inc., Ann Arbor, Michigan 69-16,127 CRABTREE, Robert Jewell, 1933Michigan State University, Ph.D., 1969 Agriculture, soil science University Microfilms, Inc., Ann Arbor, Michigan EFFECTS OF RATES AND SOURCES OF POTASSIUM ON YIELDS AND MINERAL CONTENT OF POTATOES AND EVALUATION OF POTASSIUM QUANTITY-INTENSITY RELATIONSHIPS OF SELECTED MICHIGAN SOILS By Robert Jewell Crabtree 1 ' A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Soil Science 1969 ABSTRACT EFFECTS OF RATES AND SOURCES OF POTASSIUM ON YIELDS AND MINERAL CONTENT OF POTATOES AND EVALUATION OF POTASSIUM QUANTITY-INTENSITY RELATIONSHIPS OF SELECTED MICHIGAN SOILS b y Robert Jewell Crabtree Field experiments were conducted on a McBride sandy loam soil to determine the effects of various rates and sources of potassium fertilization of Russet Burbank and Sebago potato varieities on (1) yields and specific gravity of tubers, (2) the uptake and distribution of po­ tassium, calcium, and magnesium in potato tissue, and (3) reducing sugar content of tubers at harvest Significant yield responses were obtained from application rates of K 20 as KCl up to 180 pounds per acre and from 150 pounds of K 20 as KCl, KNO^, K 2S0^, and K 2C 0 3 , but yield response was independent of potassium source. Specific gravity decreased significantly with in­ creasing applications of KCl on both Burbank and Sebago varieties, but larger decreases were noted for the Sebago Robert Jewell Crabtree variety. Potassium nitrate decreased the specific gravity on the Sebago variety when compared to KCl, K 2SO^, and K CO.. Potassium concentrations in potato tissue increased with increasing applications of K 20; however, there was a decrease in potassium content as maturation of plants occurred. The magnitude of potassium concentrations in plant tissue was petioles > leaves > whole plants > tubers. Concentrations of calcium and magnesium in potato tissue decreased with increasing rates of applied potas­ sium, but increased with maturation of the plant. calcium concentrations in petioles, The leaves, and whole plants were sixty to eighty times that found in tubers. There were no significant differences between sources of potassium and calcium uptake. 480 pounds of Applications of 240 and per acre as KCl resulted in potassium induced decreases in magnesium and calcium content of petioles, leaves, and whole plants, but the decrease in magnesium was much larger in magnitude than that of cal­ cium. Rates and sources of potassium had no significant effects on the reducing sugar content of tubers at harvest. Robert Jewell Crabtree Four oat crops were grown in the greenhouse on sixteen Michigan soils selected for variations in potas­ sium content. Potassium-uptake and yields of each oat crop were measured. On each soil, exchangeable potassium was measured and the relation between equilibrium activity ratios of potassium to calcium and magnesium (ARe ) and changes in exchangeable K (AKe) were determined. Exchangeable potassium (1 N NH^OAc extractable) was correlated with yields (r = +0.75**), total potassium- uptake (r = +0.98***), and uptake of nonexchangeable po­ tassium (r = +0.82***). Uptake of nonexchangeable potas­ sium amounted to 50 per cent or more of total uptake of potassium on all soils except three. Estimates of exchangeable potassium derived from equilibrium curves were found to be much more indicative of the total uptake of potassium (r = +0.83***) than were K the A R e values. K The potential buffering capacity (PBC ) as a single value (-AK/ARe ) gave poor correlations as an index of potassium availability. the product When PBC K was multiplied by -AK, (potassium-potential) was correlated Robert Jewell Crabtree (r = +0.56*) with the potassium-uptake of the first oat crop, but not the subsequent.c r o p s . 4 ACKNOWLEDGEMENTS The author wishes to express his appreciation to Dr. E. C. Doll for his interest and patient guidance during the course of this investigation. Appreciation is extended to Dr. R. L. Cook# Dr. H. D. Foth# Dr. N. E. Good# and Dr. B. D. Knezek for serving as members of my guidance committee. The writer would also like to thank Mrs. Nelly Galuzzi for her assistance in the statistical analyses of the data and to Mr. Max McKenzie for his help in the greenhouse phase of this work. TABLE OF CONTENTS Page A C K N O W L E D G E M E N T S .................................... LIST OF TABLES ii ...................................... LIST OF F I G U R E S ...................................... INTRODUCTION ........................................ 1 PART I. EFFECTS OF RATES AND SOURCES OF POTASSIUM ON YIELDS, SPECIFIC GRAVITY, MINERAL CONTENT, AND REDUCING SUGAR CONTENT OF POTATOES LITERATURE R E V I E W .................... 4 Potassium Deficiency Symptoms in Potato Plants 4 Effect of Rate and Source of Potassium on Yields and Specific Gravity of Potatoes 5 .. Effect of Potassium upon the Carbohydrate Composition of Potatoes .................... 6 Effects of Levels and Sources of Potassium on Absorbtion of Calcium, Magnesium, and Phosphorus by Potato Plants ................ 8 Banded Versus Broadcast Application of Potassium Fertilizers on Potatoes ......... 10 iii Table of Contents.— C o n t . Page METHODS A. B. AND MATER I A L S ............................... 15 Field Procedure............................ 16 1. Rate of Potassium S t u d y ................ 16 2. Source of Potassium S t u d y ............. 16 3. Collection of Plant Tissue Samples 17 4. The Harvesting and Specific Gravity Determination of Potatoes ......... 19 ...................... 20 Sample Preparation and Analysis of Plant T i s s u e ......................... 20 Reducing Sugar Determination in Potato Tuber T i s s u e ......................... 21 Statistical Analyses .................. 23 ............................. 25 Rate of Potassium S t u d y .................... 25 Laboratory Procedure 1. 2. 3. RESULTS A. AND DISCUSSION 1. 2. 3. 4. . . Yields and Specific Gravity of Burbank and Sebago P o t a t o e s ................ 25 Potassium Concentration in Potato Petioles ............................. 31 Potassium Concentration in Potato leaves.................. 32 Potassium Concentration in Potato P l a n t s ............................... 33 iv Table of Contents.— Cont. Page 5. Potassium Concentration in Potato Tu b e r s ............................... 34 Calcium Concentration in Potato Petioles............................. 35 Calcium Concentration in Potato Leaves ............................... 36 Calcium Concentration in Potato Plants ............................... 38 Calcium Concentration in Potato T u b e r s ............................... 38 Magnesium Concentration in Potato Petioles............................. 40 Magnesium Concentration in Potato L eaves ............................... 43 Magnesium Concentration in Potato Plants ............................... 43 Magnesium Concentration in Potato T u b e r s ............................... 45 Effect of Rates of Potassium on Reducing Sugar Content of Tubers at H a r v e s t ............................. 45 Source of Potassium S t u d y .................. 47 6. 7. 8. 9. 10. 11. 12. 13. 14. B. 1. 2. Yields and Specific Gravity of Burbank and Sebago P o t a t o e s ................ 47 Potassium Concentration in Potato Petioles............................. 48 v Table of Contents.— Cont. Page 3. Potassium Concentration in Potato L e a v e s ............................... 49 Calcium Concentration in Potato P e t i o l e s . ........................... 51 Calcium Concentration in Potato L e a v e s ............................... 52 Magnesium Concentration in Potato Peti o l e s ............................. 54 Magnesium Concentration in Potato L e a v e s ............................... 56 Effects of Sources of Potassium on Reducing Sugar Content of Tubers at H a r v e s t ........................... 56 General Discussion of Potassium Rate and Source Experiments. . . . ............. 57 4. 5. 6. 7. 8. C. PART II. EVALUATION OF POTASSIUM QUANTITY-INTENSITY RELATIONSHIPS OF SELECTED MICHIGAN SOILS LITERATURE R E V I E W .................................... Potassium Release and Fixation 61 ................ 61 Measurement of Potassium Potential and Buffering Capacity and Their Relation to the Supply of Potassium to P l a n t s ......... 67 METHODS AND MATER I A L S ............... A. Greenhouse Procedures ...................... vi 72 72 Table of Contents.— Cont. Page B. Soil Potassium Evaluation '. . . . RESULTS AND DISCUSSION ............................. 74 77 1. Yields and Potassium Uptake by Oats. . 77 2. Uptake of Exchangeable and Nonexchangeable Potassium by Oats . 81 3. Labile Potassium in S o i l s ......... 87 4. Equilibrium Activity Ratio and Potential Buffering Capacity of the S o i l s ..................... 88 5. Potassium Potential of S o i l s .... 93 6. The evaluation of exchangeable K, -AK, AR q , PBCk , and K-potential as indexes of plant available K. . . . 95 SUMMARY AND CONCLUSIONS EFFECTS OF RATES AND SOURCES OF POTASSIUM ON YI E L D S , SPECIFIC GRAVITY, MINERAL CONTENT AND REDUCING SUGAR CONTENT OF BURBANK AND SEBAGO POTATOES............... EVALUATION OF POTASSIUM QUANTITY-INTENSITY RELATIONSHIPS OF SELECTED MICHIGAN SOILS. . . 99 . 103 LITERATURE CITED ..................................... 105 A P P E N D I X ............................................... 113 vii LIST OF TABLES Page Table 1. 2. 3. 4. 5. Yield and specific gravity of Burbank and Sebago potatoes as related to rate of K fertilization ......................... 26 Significant differences between Burbank and Sebago potatoes as related to rate of K fertilization...................... 26 Dry matter content (%) of Burbank and Sebago tubers in early tuber set, tubers two-thirds to three-fourths mature, and mature tubers (76, 97, and 131 days after planting, respectively) as related to rate of K fertilization . 28 Potassium content (%) in petioles and leaves in early season, midseason, and late season (56, 76, and 97 days after planting, respectively) as affected by . rate of K f e r t i l i z a t i o n ............. 29 Potassium content (%) in plants and tubers in early tuber set, tubers two-thirds to three-fourths mature, and mature tubers (76, 97, and 131 days after planting, respectively) as affected by rate of K f e r t i l i z a t i o n ................ 30 Calcium content {%) in petioles and leaves in early season, midseason, and late season (56, 76, and 97 days after planting, respectively) as affected by rate of K f e r t i l i z a t i o n ................ 37 viii List of Tables.— Cont. Table 7. 8. 9. Page Calcium content (%) in plants and tubers in early tuber set# tubers two-thirds to three-fourths mature# and mature tubers (76# 97# and 131 days after planting# respectively) as affected by rate of K f e r t i l i z a t i o n ................ 39 Magnesium content {%) in petioles and leaves in early season# midseason# and late season (56# 76# and 97 days after planting# respectively) as affected by rate of K f e r t i l i z a t i o n ................ 41 Magnesium content (%) in plants and tubers in early tuber set# tubers# two-thirds to three-fourths mature# and mature tubers (76# 97# and 131 days after planting respectively) as affected by rates of K fertilization................ 44 10 . Per cent reducing sugar in tubers on a 11. 12 . fresh weight basis as related to rate of K fertilization...................... 46 Yield and specific gravity of Burbank and Sebago potatoes as affected by source of K fertilization...................... 47 Significant differences between Burbank and Sebago potato yields as affected by source of K f e r t i l i z a t i o n ............. 48 Potassium content {%) in petioles and leaves at early season# midseason# and late season (62# 83# and 104 days after planting# respectively) as affected by source of K f e r t i l i z a t i o n ............. 50 ix List of Tables.— Cont. Table 14. 15. 16. 17. 18. 19. 20. 21. Page Calcium content {%) in petioles and leaves at early season* midseason* and late season (62* 83* and 104 days after planting* respectively) as affected by source of K fertilization . . . . . . . 53 Magnesium content {%) in petioles and leaves at early season* midseason* and late season (62* 83* and 104 days after planting* respectively) as affected by source of K f e r t i l i z a t i o n ............. 55 Per cent reducing sugar in tubers on a fresh weight basis as related to source of K fertilization...................... 57 Extractable cations and p H prior to cropping for 16 Michigan soils used in greenhouse and laboratory evaluations . 73 Yields of four oat crops grown in green­ house on sixteen Michigan soils without added p o t a s s i u m ........................ 78 Potassium uptake b y each of four crops and the total uptake by oats grown in greenhouse on sixteen Michigan soils without added potassium ................ 79 Correlation between exchangeable potassium prior to cropping; uptake of potassium and yields of four crops of oats grown in greenhouse on 16 Michigan soils. . . 82 Uptake of exchangeable and nonexchangeable potassium by four crops of oats grown in greenhouse on 16 Michigan soils. . . 83 x List of Tables.— Cont. Table 22. 23. 24. 25. 26. Page Nonexchangeable potassium taken up by each oat crop and total uptake of nonex­ changeable p o t a s s i u m .................... 84 Exchangeable potassium in 16 Michigan soils before and after four oat crops were grown in the greenhouse.................. 85 Summary of soil potassium properties derived from equilibrium experiments before and after cropping ................ 89 Correlation between -AK prior to cropping? potassium uptake, and yields of oats grown in greenhouse on 16 Michigan s oils...................................... 92 Correlation coefficients relating exchange­ able K, -AK, A R q , PBCk , and K-potential with potassium uptake and yields of four oat crops grown in greenhouse on 16 Michigan soils ........................... 96 xi LIST OF FIGURES Figure Page 1. Relation of potassium activity ratio (ARe ) to ,-AK before and after cropping on Charity clay loam 1 ......................... 114 2. Relation of potassium activity ratio (ARg ) to -AK before and after cropping on Charity clay loam I I ....................... 115 3. Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Lenawee clay l o a m ........................... 116 4. 5. 6. 7. 8. K Relation of potassium activity ratio (ARfi) to -AK before and after cropping on ........................117 Sims clay loam I . Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Sims clay loam I I ........................... 118 K Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Sims clay loam I I I ......................... 119 K Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Colwood l o a m ................................120 Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Conover l o a m ................................121 xii List of Figures.— C o n t . Figure 9. 10. Page Relation of potassium activity ratio (AR0 ) to -AK before and after cropping on Miami l o a m .................................. 122 K Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Hettinger silty clay loam....................123 11. Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Brimley silt l o a m ........................... 124 12. Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Breckenridge sandy l o a m..................... 125 13. Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Hillsdale sandy loam . . . . . ........ 126 Relation of potassium activity ratio (AR0 ) to -AK before and after cropping on Hodunk sandy l o a m ...................... . 127 14. 15. 16. K Relation of potassium activity ratio (ARe ) to -AK before and after cropping on McBride sandy l o a m ......................... 128 Relation, of potassium activity ratio (ARe ) to -AK before and after cropping on Metamora sandy l o a m ......................... 129 xiii EFFECTS OF RATES AND SOURCES OF POTASSIUM ON YIELDS AND MINERAL CONTENT OF POTATOES AND EVALUATION OF POTASSIUM QUANTITY-INTENSITY RELATIONSHIPS OF SELECTED MICHIGAN SOILS INTRODUCTION In most areas of Michigan potassium (K) are needed for maximum production of potatoes. fertilizers The amount of K fertilizer required at any specific location can best be determined by means of soil tests which have been cali­ brated with field experiments. Considerable research has been done to correlate laboratory measurements of soil K with response of potatoes to K fertilizers# but no one method of measuring the level of soil K has been entirely satisfactory. Exchangeable soil K has generally been used as an index of available K; however, analyses of the soil solution have also been used to obtain an index of K availability to plants. During growth of a single crop more K may be re­ moved from the soil than is -present in both the soil 2 solution and in exchangeable form. Exchangeable K plus estimates of nonexchangeable K which may be released during cropping have been widely used as a criteria for measure­ ment of available K in soils. More recently# available soil K has been defined by intensity and capacity factors: the intensity' factor is derived from the activity of K in the soil solution# and the capacity factor from soil ex­ changeable and nonexchangeable K. The investigations reported herein are composed of two parts# a field experiment and a greenhouse and labora­ tory experiment. The objectives of the field investigation were to compare the effects of rates and sources of K on (1) yields and specific gravity of tubers# and distribution of K# calcium (2) the uptake (Ca), magnesium (Mg) in potato tissue# and (3) reducing sugar content of tubers at harvest. The objectives of the greenhouse and laboratory studies were (1) to evaluate various intensity and capacity factors of soil K in 16 Michigan soils and (2) relate these factors to yield and uptake of K by four successive crops of oats grown in the greenhouse. PART I EFFECT OF RATES AND SOURCES OF POTASSIUM ON YIELDS, SPECIFIC GRAVITY, MINERAL CONTENT, AND REDUCING SUGAR CONTENT OF POTATOES LITERATURE REVIEW Potassium Deficiency Symptoms in Potato Plants Potassium (K) deficiency in potatoes by Knowles et al.# 1940; Cook# 1962; Wallace# (as described 1961) re­ sults in retarded growth and shortening of the internodes# which give the plants a compact appearance. Leaves become crinkled# droop# and are reduced in size due to narrow arrangement of the leaflets which form a sharp angle with the stem. Appearance of abnormally dark green foliage is an early indication of K shortage. Later# older leaves become yellowish# and a brown or bronze color develops# starting at the tip and edge and gradually affecting the entire leaf. The lower leaves may dry up at the same time leaving a tuft of green leaves at the top of the plant. If severe K deficiency develops# tually dies. 4 the entire plant even­ 5 Effect of Rate and Source of Potassium on Yields and Specific Gravity of Potatoes Herman and Merkle (1963) studied the effects of rates and sources of K on potato yields and quality. In field trials at seven locations in the major potato grow­ ing areas of Pennsylvania# potato yields were not increased when more than 66 pounds of K per acre were applied as either KCl or if the exchangeable soil K was higher than 200 pounds per acre. Soil variability# moisture con­ tent#. and variety differences apparently affected the yield response of the potatoes as much as the source of K. How­ ever# specific gravity of tubers was lower when KCl was applied at rates of 133 and 199 pounds K per acre than when equivalent amounts of K were applied as ^ S O ^ . Rowberry et al. (1963) studied rates and sources (KCl and K 2SO^) of K fertilizers on potatoes grown on min­ eral soils in Ontario. Although there were some increases in yield from rates of fertilizer higher than 1000 pounds per acre# yields were generally not increased when more than 1500 pounds per acre of 6-12-12 was applied. However# specific gravity decreased with increasing rates of fertil­ izer# and also increased with increasing replacement of the chloride salt by the sulfate salt. 6 Murphy and Goven (1965) compared applications of K SO. and KCl on Russet Burbank potatoes in Maine. 2 4 Yields and specific gravities were not significantly affected by source of K but surface russeting was better when was used as a source of K. The results of a ten-year investigation (Murphy and Goven* 1966) on Katahdin potatoes in Maine indicated that (1) source of K did not influence yield of potatoes* specific gravity was higher when (2) or KNO^ were used as K fertilizers than when KCl was applied* (3) potatoes fer­ tilized with KCl tended to produce chips of lighter color than did those fertilized with or KNO^ and (4) spe­ cific gravity of the tubers was lower and potato chips tended to be lighter in color for all sources as the rate of K fertilization was increased. Effect of Potassium Upon the Carbohydrate Composition of Potatoes The relation of K to the carbohydrate metabolism of potatoes has not been clearly established. 1950) Terman (1949* reported that the starch content of potato tubers is 7 usually decreased as the rate of K fertilization is in­ creased on very fertile soil. Ward (1959) observed a de­ crease in total starch content at high rates of K fertili­ zation due to a stimulation of the decomposition of car­ bohydrate reserves. Smith and Nash (1942) reported that carbohydrate production and ultimate starch accumulation were lower in tubers grown in soils to which high rates of chlorides (Cl) had been applied. Houghland and Shricker brough (1933) (1933) and Ware and Kim­ reported that the total starch content of potato tubers was not affected by sources of K fertilizers when KCl and K 2SO^ were applied. Lucas et al. (1954) re­ ported that tubers fertilized with KCl contained 1.3% less starch and were 6% lighter in weight than those fertilized with K 2SC>4 . There is some evidence that the various anions associated with K fertilizers may differentially influence the enzyme content or the functions of enzymes in potatoes# and thus indirectly affect the starch and dry matter con­ tent. James (1930) states that "application of K increases catalytic activity and/ therefore# may increase the effi­ ciency of starch formation." Latzko (1955) found that the 8 hydrolytic activity of carbohydrases# such as invertase# amylase# and £-glucosidase# is inhibited by Cl” ions# and increased b y sulfate Mulder (1956) (SO*) ions. noted that K affected the rate of potato tuber respiration more than N» P# Mg# or Ca. Po­ tassium deficient tubers had higher respiration rates than tubers grown with an optimum K supply. The increased rate of respiration was attributed to easier bruising of Kdeficient tubers. The increased respiration rate of bruised tuber tissue was related to a stimulation of re­ spiration of healthy cells by substances derived from the damaged cells and diffusing to the intact cells. Effects of Levels and Sources of Potassium On Absorption of Calcium# Magnesium# and Phosphorus by Potato Plants High rates of K applied to soils can induce magne­ sium (Mg) deficiency in crops Hovland and Caldwell# (Adams and Henderson# 1960? Lucas and Scarseth# 1962? 1947). Tissue of Mg-deficient plants frequently contains low levels of Mg and high levels of K. It is difficult to establish any meaningful ratios between these ions to 9 define deficiency or sufficiency levels in various plants. However, Hossner et al. (1968) reported that when soil K:Mg ratio exceeded 5:1, K-induced Mg deficiency occurred on potatoes grown on an acid sandy podzol in northern Mich­ igan. Scharrer and Mengel (1958) reported that a physio­ logical antagonism exists between K and Mg which is inde­ pendent of the colloidal effects of the soil and of the anion of-the K salt applied. They suggest that this an­ tagonism is restricted to the green tissue and showed that it i-s most prevalent in the leaves. Wilcox (1961) grew potatoes on a Genessee sandy loc^m soil with broadcast applications of 0, 75, 150, and 225 pounds per acre of K^O applied either as KC1 or I^SO^. To intensify the anion effect, N was applied as (NH^) 2 S 0 4 with K.SO. treatments and as NH.C1 with KC1 treatments. 2 4 4 Sixty-six pounds per acre of N were applied with the basic treatment. The N and K fertilizer were broadcast and disked into the soil just before planting. In 1959, a 32-128-0 fertilizer treatment was applied in a band and in 1960 a 44-192-0 fertilizer treatment was applied in a band at planting time. Tissue samples at the prebloom stage 10 showed no difference in P composition due to treatment in 1959 and 1960. However* samples collected at time of tuber development in 1960 showed a reduction of P concentration as K fertilizer rate increased. The percentage K in the tissue was increased and that of Ca and Mg decreased as rates of K fertilizer were increased. Percentages of Ca and Mg in the tissue was higher when Cl salts were applied than when SO^ salts were applied. Banded Versus Broadcast Application of Potassium Fertilizers on Potatoes Cooperative field investigations on fertilizer placement for potatoes conducted from 1931 to 1937 in Maine# Michigan* New Jersey* New York* and Ohio were summarized by Cummings and Houghland follows: (1939) . The chief comparisons were as (1) fertilizer in two bands# one on each side of and level with the seed piece at distances of 1# 2* and 4 inches from the seed piece; (2) in bands on each side and 2 inches below the seed piece; seed piece; (4) (3) a single band above the in a single band underneath seed piece# with 1 to 2 inches of fertilizer-free soil interposed; 11 (5) in furrow# lightly mixed with soil# and (6) in furrow well-mixed with soil. Placement of the fertilizer in a band immediately under or above or mixed with the soil around the seed piece usually resulted in delayed emergence of the sprout and reduction in yield. Fertilizer placed in a band at each side of the row resulted in more rapid emergence of sprouts# more vigorous plant growth# and higher yields than the other methods of application. Cooke (1953) summarized the results of 29 experi­ ments conducted in England from 1945 to 1947 # and recom­ mended that fertilizer be placed in two bands# one on each side of the row# for most efficient utilization of fertil­ izer applied at rates normally required to give maximum yields. In wet or normal rainfall years# no harmful ef­ fects were noted when the fertilizer was placed in contact with the seed. In an abnormally dry year (1947)# however# growth was severely retarded at several locations when heavy fertilizer applications were placed in contact with the seed# and yields were decreased as compared to those obtained when fertilizer was placed in side bands. 12 The effectiveness of fertilizer which was broadcast and plowed down was compared to that when fertilizer was placed in bands on each side of the seed piece on a Caribou loam soil at Aroostook Farm# Presque Isle# Maine# and 1944 in 1943 (Chucka et al.> 1944y Hawkins et al.# 1947; and Chucka et alJ# 1945). In these tests# the total amount of nutrients applied per acre in each case was equivalent to 2#000 pounds per acre of 6-6-12 fertilizer. application included before plowing# The types of (1) broadcasting all the fertilizer (2) plowsole placements# all the fertilizer after plowing# and row applications# and (3) broadcasting (4) combining plow-down (5) placing all fertilizer in side bands. Although some of the other methods of application resulted in yields as good or slightly better than when all the fertilizer was placed in side bands# none of them were consistently superior to side banding in either a wet year (1943) or a dry (1944) season. It was concluded that under the conditions of the experiments# there was no advantage in varying the placement from applying all fertilizer in side bands. 13 Berger et al. (1961) conducted field trials in Wisconsin using three different soil types and three p o ­ tato varieties to compare band and broadcast applications of K salts containing chlorides and sulfates. They con­ cluded that chlorides, banded in the row with P and N fertilizers, will inhibit P uptake and reduce yield and dry matter content of potatoes as compared to sulfates. Separating the KC1 from the P fertilizer, by broadcasting the KC1 and banding the P, increased P uptake and yields in most cases. Potassium sulfate was considered a better source of K than KC1 when applied banded in the row with the P and N fertilizer. In general, sulfate of potash- magnesia appeared to be the best source of K for both in­ creasing potato yields and improving quality. Hawkins (1965) reported that experiments conducted in Connecticut where one half of the K either as KC1 or K 2S°4 waS P^owe^ down resulted in as good or slightly better potato yields than applying all the fertilizer in the row using side bands at planting. Under the dry spring conditions of 1963 at locations where irrigation was not used, potatoes which received 75% of the K as a sidedressing (when the plants were at the 3-5 inch stage) were more 14 vigorous and produced slightly larger yields than those ^which received all the K in side bands at planting. This was true whether chloride, sul f a t e , or nitrate of K was used. However, the best growth, yield, and dry matter content were obtained with K N O ^ . In 1964, on a soil limed to pH 5.4 and' testing medium in available K, applications of K C l , either plow-down or broadcast after plowing, were compared with all the K applied in side bands at planting. The plow-down or broadcast treatments resulted in improved early growth under the dry soil conditions in the spring and in equal or slightly higher yields as compared to K applied in side bands. METHODS AND MATERIALS In May# 1967# experiments to determine the effects of various rates and sources of K fertilizers on potato yields were initiated on a McBride sandy loam soil at the Montcalm Experimental Farm in Montcalm County# Michigan. Experiments were laid out in a randomized complete block design with 4 replications with each experimental plot being 50 feet long and 16 feet wide and potatoes were planted in 32 inch rows. Of the six potato rows in each plot# three were planted to the Russet Burbank variety# and the other three to the Sebago variety. On all plots# an equivalent of 60 pounds N per acre as NH^NO^ was plowed down and another 60 pounds N was banded at planting along with 100 pounds per acre of P o0_ as 0-46-0. 2 5 When banding procedure was used# the fertilizer was placed in 2 bands# 2 inches on either side and level with the seed piece. Potatoes were planted on May 13 # 1967. 15 16 A. 1. Field Procedure Rate of Potassium Study Prior to fertilizer application on the experimental area where rates of K were compared# the soil tested pH 6.6# available P was 154 pounds per acre# and extractable K# Ca, and Mg were 210# 1426# and 141 pounds per acre respectively. Soil pH was determined in a 1:1 soil:water suspension using a glass electrode potentiometer. Available phosphorus was extracted for 1 minute with Bray P-l reagent (0.025 N HC1 and 0.03 N N H ^ F ) # using a 1:8 soil:extractant ratio. Ca­ tions were extracted for 1 minute with 1.0 N NH^0Ac(pH 7.0) using a 1:8 s o i l :extractant ratio. Six levels of K were established by applying the equivalent of 0# 60# 120# 180# 240# or 480 per acre as KC1. pounds of 1^0 All K was banded at planting except when 480 pounds K 2<0 was appliedy in this treatment# 360 pounds per acre of K^O was broadcast and plowed down# and 120 pounds per acre of 1^0 was applied in bands at planting. 2. Source of Potassium Study On the area where sources of K were compared# soil test values were as follows: the pH 6.7# 150 pounds P 17 per acre* and 270# 1336# and 140 pounds per acre of e x ­ changeable K# Ca# and Mg respectively. Potassium was applied in bands at planting at a rate to supply 150 pounds K 20 per acre as KC1# KNO^ # K 2SC>4 # or K C O . to to A check treatment was included to which no K was applied. 3. Collection of Plant Tissue Samples On July 8# when the plants were 12-14 inches high# petiole and leaf samples were obtained from plants where rates of K were compared# and subsequent samples were taken on July 28# and August .18. Each sample consisted of 40 to 50 petioles from the fourth leaf below the growing tip of the plant# which is the youngest fully expanded leaf of the plant. The petiole samples consisted of that portion of the plant between the stem and the base of let while the leaf samples consisted of the the first leaf­ leaves removed from the end of the petioles. Whole plant samples the soil surface) (that part of the plant above and the tubers under those plants were obtained on July 28# August 18# and September 21# 1967. 18 Eight whole plants were chosen at random on one end of the plots at each sampling date. Where sources of K were compared# petiole and leaf samples were taken as described above on July 14# August 4# and August 25# 1967. Since length of growing season for potatoes varies widely# even within the same locality# plants and samples were classified according to their physiological age as well as b y time from planting. Under certain ideal condi­ tions tubers may be harvested within 90-100 days from plant­ ing while under other conditions the crop may be grown for as long as 150 days# as in the case of this study. In this study# plants emerged about two and one half weeks after planting. The results relating to the mineral concentration in petioles and leaves of the first sampling date will be classified as "early season" which is as soon as plants are large enough petiole samples. (12-14 inches high) to provide adequate The second sampling will be considered "mid-season#" which is that time from blossoming to and including tuber set. The third sampling is considered "late season" and is that period when the tubers are one 19 half to three-fourths mature. With respect to the discus­ sion of mineral content of whole plants and tubers* the first sampling date will be considered "early tuber set#" the second date "late season" when the tubers are two- thirds to three-fourths mature# and the third samplirg date "mature" w h e n tubers have matured. 4. The Havesting and Specific Gravity Determination of Potatoes Potatoes- from the two inside rows for a length of 30 feet on the rate of K experiment# and of 50 feet on the source of K experiment#were harvested for yields on Octo­ ber 12* 1967. Specific gravity determinations were made by the hydrometer method as described b y Smith (1950). An 8-pound sample of potatoes was placed in a wire basket and the basket suspended from the bulb of the hydrometer. The sample and hydrometer were then immersed in water# and the specific gravity readings were obtained at the water level on the scale in the hydrometer tube. 20 B. Laboratory Procedure 1. Sample Preparation and Analysis of Plant Tissue Twelve potato tubers from each treatment and for each sampling date were thoroughly washed in tap water and rinsed under distilled water to remove soil particles and then sliced. petioles* All plant samples (the sliced tuber tissue* leaves* and whole plants) were dried at 65°C and ground to pass a 20 mesh sieve. All tissue samples were dry ashed according to the procedure of Peech as described b y Jackson (1958). One g. of oven-dried tissue was ashed at 400-425°C for 15 hours. After cooling* 25 ml. of 1 N HN03 was added to the ash# and evaporated to dryness on a hot plate. The residue was again placed in a muffle furnace at 400°C for 10 minutes# cooled* and then dissolved in 25 ml. of 1 N HC1. The re­ sulting solution 'was filtered and diluted to 100 ml. for the cation determinations. Potassium in the filtrate was determined using a Coleman Model 21 flame photometer; Mg and Ca were deter­ mined in a diluted filtrate*'using a Perkin Elmer Model 290 21 and 303 atomic absorption spectrophotometer respectively; 1500 ppm La was added to the diluted filtrate to eliminate interference from other ions (Doll and Christenson# 1966). 2. Reducing Sugar Determination in Potato Tuber Tissue Ten tubers from each plot were sampled by forcing a small cork borer through the tuber longitudinally from the stem end to the bud end. Twenty-five g. of tuber tissue were collected in this manner and this then made up to 100 g . with reagent grade methanol. The 25 g. of tuber tissue and methanol were poured into a blender and ground for 2 minutes at the high blend­ ing speed. After blending# the slurry was filtered through Whatman No. 2 filter paper and the filtrate was used for sugar evaluation. A low-alkalinity copper reagent was made according to the procedure of Somogyi (1950) by dissolving 12 g. of sodium potassium tartrate and 24 g. of anhydrous sodium carbonate in about 250 ml. of H^O. A solution of 4 g. of cupric sulfate pentahydrate in 50 ml. of H^O was added while stirring# followed b y 16 g. of sodium hydrogen 22 carbonate. A solution of 180 g. of anhydrous sodium sul­ fate in 500 ml. of H^O was boiled to expel air, then the two solutions were combined and diluted to 1 liter. After standing one week the clear supernatant solution was used in the procedure given below. An arsenomolybdate reagent was prepared as de­ scribed by Nelson (1944). Twenty-one ml. of 96% sulfuric acid was added to 25 g. of ammonium molybdate in 450 ml. of H^O followed by 3 g. of disodium hydrogen arsenate heptahydrate dissolved in 25 ml. of H^O. The mixed solu­ tion was incubated 24 hours at 37°C and stored in a glass stoppered brown bottle until ready for use. To 1 ml. of the sugar solution samples, blanks, and standard sugar solutions, an equal volume of the lowalkalinity copper reagent was added, heated 10 minutes in a vigorously boiling water bath, and then cooled. One ml. of arsenomolybdate reagent was added and when all the cuprous oxide was dissolved after mixing, the solution was diluted to 50 ml. and allowed to stand at least 15 minutes but not more than 40 minutes. Absorbances were read at 540 m(i in a Bausch and Lomb colorimeter. Percent trans­ mission was converted to milligrams reducing sugar by 23 reference to a standard curve prepared by using known amounts of reducing sugar. The data were calculated as percent reducing sugar on fresh weight basis. 3. Statistical Analyses Data were statistically analyzed utilizing a Con­ trolled Data Corporation (CDC) 3600 digital computer. All data from the K rate and source experiments were subjected to analyses of variance using a split block design with K treatments as the whole-plot and potato varieties as the sub-plots. The data concerning the K, Ca. and Mg concen­ trations in petioles, leaves, whole plants, and tubers were first analyzed for differences between treatments at each time of sampling and then combined and analyzed to deter­ mine if a difference existed for the same treatment between sampling dates. No significant interaction between K rate or source of K and the two varieties were noted with respect to K, Ca, and Mg in potato petioles, leaves, plants, and tubers. All discussion concerning the mineral content will there­ fore be on the basis of an average of both varieties. 24 The "honest significant difference" posed b y Tukey (Steel and Torrie, (hsd) as pro­ 1960) was calculated from the results of the analyses of variance. Larger di f­ ferences between means are required for significance using the hsd as compared to the "least significant difference" (lsd) resulting in a more rigorous test for significant differences. RESULTS AND DISCUSSION Field experiments on Burbank and Sebago potato varieties were conducted to compare the effects of various rates and sources of K on: of tubers, (1) yields and specific gravity (2) the uptake and distribution of K, Ca, and Mg in potato tissue, and (3) reducing sugar content of tubers at harvest. A. Rate of Potassium Study 1. Yields and Specific Gravity of Burbank and Sebago Potatoes Yields of both Burbank and Sebago potatoes were in­ creased when K fertilizer was applied (Tables 1 and 2). application of 120 or 180 pounds of 1^0 per acre resulted in higher yields than when 60 pounds of I^O was applied, but when 240 or 480 pounds K-0 were applied, yields were lower than those obtained when 120 or 180 pounds were applied (Table 2). 25 An 26 TABLE 1.— Yield and specific gravity of Burbank and Sebago potatoes as related to rate of K fertilization Burbank Pounds K 2 O Per Acre Yield (Cwt/A) Sebago Specific Gravity Yield (Cwt/A) Specific Gravity 0 203 1.091 210 1.090 60 212 1.090 226 1.089 120 275 1.090 299 1.089 180 242 1.089 291 1.088 240 214 1.088 208 1.085 480 228 1.088 232 1.085 hsd (.05) ns .002 .003 ns TABLE 2.— Significant differences between Burbank and Sebago potato yields as related to rate of K fertilization Probability Level Comparison Burbank No K vs. K 20 120 v s . 180 l b s . K 20 60 vs. 120 and 180 lbs. K 20 240 vs. 480 lbs. K 20 120 and 180 vs. 240 and 480 lbs. K 20 Sebago .05 .05 ns ns .05 .05 ns ns .05 .05 27 Specific gravity decreased with increasing rates of KC1 on both Burbank and Sebago potato varieties# this decrease was most pronounced for Sebagoes and (Table 1). The differences in dry matter content were evident through­ out the growing season from the time of early tuber set (Table 3) # although the percentage of dry matter in the tubers increased as the plants matured. The decrease in dry matter may in part be attributed both to an increase in K uptake by the plants (Tables 4 and 5) and to a prob­ able increase in Cl uptake as has been reported 1950; Dunn and Rost# 1948; Nelson and Hawkins# rates of KC1 are increased. (Terman# 1947) when Increased Cl content has the effect of decreasing the starch content of potatoes et al.# 1954; Smith and Hash, (Lucas 1942; Terman# 1949; Terman# 1950) . A possible explanation for the decrease in both yields and specific gravity is that large doses of Cl de­ crease the total amount of carbohydrates in the leaves# apparently caused by reduced chlorophyll content and weak­ ened photosynthetic activity (Baslavskaga# 1936). and Gausman (1960) Corbett suggest the possibility that a high Cl treatment might shunt the carbohydrate metabolism into the TABLE 3.— Dry matter content (%) of Burbank and Sebago tubers in early tuber set# tubers two-thirds to three-fourths mature# and mature tubers (76# 97# and 131 days after planting# respectively) as related to rate of K fertilization Percent Dry Matter Pounds K 20 Per Acre - Sebago Burbank 76 days 97 days 131 days 76 days 97 days 131 days 0 23.9 24.2 26.6 23.3 24.8 26.2 60 23.6 24.4 26.4 23.3 23.1 25.5 120 23.9 23.4 24.9 22.2 23.9 26.2 1Q0 21.9 22.6 24.7 21.2 22.7 25.4 240 22.2 22.4 24.0 21.4 22.0 24.3 480 22.2 21.8 24.6 20.9 21.2 24.2 1.5 1.2 1.5 .96 .88 .68 hsd (.05) TABLE 4 . — Potassium content (%) in petioles and leaves in early season# midseason# and late season (56# 76# and 97 days after planting# respectively) as affected by rate of K fertilization Potassium Content (%) * Petiokes Per Acre 56 days 76 days 97 days Average 56 days 76 days 97 days Average 0 9.04 6.32 2.69 6.02 4.49 2.00 1.63 2.71 60 11.30 6.43 3.07 6.93 4.63 2.24 1.81 2.89 120 11.55 7.01 4.01 7.52 4.85 2.42 2.07 3.11 180 12.14 8.21 5.19 8.51 5.01 2.80 2.49 3.43 240 12.44 9.38 5.98 9.27 5.40 3.09 2.66 3.72 480 12.78 10.61 7.64 10.34 5.87 3.83 3.24 4.31 (.05) .52 .30 .23 .10 ns .84 .57 .73 (.01) .66 .38 .29 .14 ns ns .72 .97 hsd TABLE 5.— Potassium content {%) in plants and tubers in early tuber set, tubers two-thirds to three-fourths mature, and mature tubers (76, 97, and 131 days after planting, respectively) as affected b y rate of K fertilization Potassium Content Pounds K^O Per Acre (%) Whole Plants 76 days 97 days 131 days 0 2.64 1.75 0.45 60 3.21 2.10 120 3.67 180 Tubers 76 days 97 days 131 days 1.61 1.76 1.57 1.42 1.58 0.52 1.94 1.86 1.71 1.52 1.69 2.74 0.59 2.33 2.00 1.89 1.61 1.83 4.72 3.72 1.10 3.18 2.28 2.05 1.78 2.03 240 5.12 3.91 1.26 3.43 2.38 2.19 1.80 2.12 480 5.61 4.80 1.63 4.01 2.65 2.40 2.09 2.37 hsd Average Average (.05) 1.04 .94 .68 .58 .27 .23 .23 .19 (.01) 1.31 1.18 .86 .80 .34 .29 .29 .25 31 triose phosphate to pyruvate pathway by increasing the in­ organic P in the plant. output, weight. This would result in a high CC^ low energy release, and result in a decrease in dry From the literature reviewed, it appears that the exact function of chloride in potato plant nutrition as re­ lated to yields and specific gravity is not yet known. 2. Potassium Concentration in Potato Petioles No significant interaction between rate of applied K and potato variety was obtained with respect to K content of potato petioles, leaves, plants, or tubers. Data rela­ tive to the K content of the plants therefore are presented as an average of the two varieties. Potassium concentration in the petioles tended to increase with increasing rates of K^O, although the concen­ tration of K in the tissue decreased with maturation (Table 4). In the early season sampling (56 days after planting), K in the petioles was higher when K fertilizer was applied than whgn. no K was applied, and the petioles from the 240 and 480 pound 1^0 treatments contained more K than those from the 60 and 120 pound K^O treatments (Table 4). 32 At midseason (76 days after planting) * the K concentration in the petioles increased with each additional increment of applied K-0 (Table 4). after planting) At the late season (97 days sampling* the petioles contained less K than the early or midseason samplings; however* the K content in petioles increased with each increment of ap­ plied K20 (Table 4). W h e n all sampling dates were averaged for each treatment the K concentrations in petioles were higher with increasing increments of K (Table 4). 3. Potassium Concentration in Potato Leaves As in the petioles# the K concentration in potato leaves tended to increase with increasing rate of 1^0 application* but the K content of leaves was only about one half that of the petioles season sampling (Table 4). (56 days after planting) At the early no significant differences in K concentrations of potato leaves were noted between rate of K treatments. after planting) At midseason (76 days the K content in leaves increased (0.05 level) when 480 pounds K^O was applied as compared to the 33 0* 60# 120# and 180 pdund treatments late season sampling (Table 4). At the (97 days after planting) # the leaves from the 180# 240# and 480 pounds of applied K^O treatments were significantly higher in K content when compared to no K. Leaves on plants to which a treatment of 480 pounds of 0 was applied had significantly higher K concentration k £ than treatments of 60 # 120 # 180 pounds of I^O (Table 4) . When all sampling dates were averaged for each treatment (Table 4)# the leaves from the 240 and 480 pound K_0 treatments were higher in K content than those from 4m the 60 pound and no 1^0 treatments. 4. Potassium Concentration in Potato Plants The K concentration in whole plants increased as the rate of applied 1^0 increased and concentrations were more similar to those found in leaves than in petioles (Table 5) . Concentrations of K in plants at early tuber set (76 days after planting) of applied K 0 (Table 5). three-fourths mature increased with each increment When tubers were two-thirds to (97 days after planting) the K con­ centration in whole plants decreased as compared to the 34 concentrations at early tuber set. stage of growth# At this physiological the K content in whole plants from treat­ ments of 180# 240# and 480 pounds of applied K^O were higher than those from the 60 pound 1^0 and no K treat­ ments (Table 5). Concentration of K in the whole plants when tubers were fully mature (131 days after planting) were only about one-third of that at the earlier samplings. When all sampling dates were averaged for each treatment the K concentration was higher in whole plants with an application of 480 pounds of K^O when compared with the no K# 60# 120# and 180 pound of applied I^O treat­ ments (Table 5). These data indicate that the magnitude of seasonal fluctuation in K concentrations of whole plants is less than that found in petioles. 5. Potassium Concentration in Potato Tubers Potassium concentrations in potato tubers# as an average of both varieties# are considerably less when com­ pared to petioles# leaves# and whole plants at the early tuber set stage of physiological development 5) . At early tuber set (Tables 4 and (76 days after planting) K content 35 in tubers from treatments which received 180# 240# and 480 pounds of K 20 was higher than those from the no K treat­ ment# and the K content in tubers from the 480 pound K 20 treatment was higher than those from the 60 and 120 pounds K 20 treatments (Table 5). three-fourths' mature When tubers were two-thirds to (97 days after planting) K content decreased slightly and the significant differences in K content of tubers between treatments were the same as at early tuber set. When tubers were mature (131 days after planting) # the same general differences in K content of tubers between treatments were apparent# b u t the total K content was less (Table 5). Potato tubers have the least amount of seasonal variation in K content when compared to petioles# leaves# and whole plants (Table 5). 6. Calcium Concentration in Potato Petioles No significant interaction between rate of applied K and potato variety was obtained with respect to Ca con­ tent in potato petioles# leaves# plants# and tubers. cium content of the plant tissue is an average of both potato varieties. Cal­ __ 36 Although Ca in petioles tended to decrease as rate of applied K increased and to increase as the plant matured, these differences were not statistically significant in any sampling date or when values for all sampling were averaged (Table 6) . 7. Calcium Concentration in Potato Leaves In general, Ca concentration in potato leaves in­ creased as the plant matured, and decreased as the rate of applied K was increased (Table 6), although these differences were not statistically significant at the early season (56 days after planting) planting) sampling. At midseason (76 days after the concentration of Ca in the potato leaves when 240 and 480 pounds of 1^0 were applied was less than that when no K was applied (Table 6). after planting) At late season (97 days the Ca content of potato leaves was less when 240 and 480 pounds of K^O were applied than when 60 pounds K 20 and no K were applied (Table 6). When all sampling dates for each treatment were averaged (Table 6) the concentration of Ca in the potato leaves when 240 and 480 pounds of K^O were applied was less than that when 60 pounds and no 1^0 were applied. TABLE 6.— Calcium content (%) in petioles and leaves in early season# midseason# and late season (56# 76# and 97 days after planting# respectively) as affected by rate of K fertilization J Calcium Content Pounds K 0 2 Per Acre Petioles 56 days 76 days 97 days 0 1.22 1.39 1.59 60 0.99 1.35 120 1.09 180 (%) Leaves 56 days 76 days 97 days 1.40 1.62 1.98 2.35 1.98 1.67 1.34 1.30 1.97 2.39 1.88 1.36 1.73 1.39 1.44 1.83 2.19 1.82 0.93 1.35 1.71 1.33 1.26 1.76 2.21 1.73 240 1.03 1.25 1.61 1.29 1.33 1.60 1.94 1.62 480 1.05 1.22 1.66 1.30 1.27 1.63 1.94 1.61 hsd Average Average (.05) ns ns ns ns ns .23 .37 .20 (.01) ns ns ns ns ns .29 .45 .29 38 8. Calcium Concentration in Potato Plants Whole plant concentrations of Ca decreased with increasing rates of applied K^O (Table 7) and were similar to the trends observed for petioles and leaves At early tubar set (76 days after planting) (Table 6). plants from plots to which 180» 240» and 480 pounds of 1^0 had been applied contained less Ca than those from plots to which no K had been applied (Table 7). thirds to three-fourths mature When tubers were two- (97 days after planting) * the concentration of Ca in plants was not affected by applications of K. after planting) When tubers were mature (131 days Ca in the whole plants was higher than at previous samplings# and Ca still tended to decrease as rate of K^O was increased (Table 7). When all sampling dates were averaged for each treatment the Ca concentra­ tions in whole plants were not significantly different (Table 7) . 9. Calcium Concentration in Potato Tubers Calcium concentrations in potato tubers# as an average of both varieties# ranged from 0.02 to 0.03 per TABLE 7.— Calcium content (%) in plants and tubers in early tuber set# tubers twothirds to three-fourths mature# and mature tubers (76# 97# and 131 days after planting# respectively) as affected by rate of K fertilization Calcium Content Pounds K^O Whple Plants Tubers 76 days 97 days 131 days Average 0 2.02 1.94 2.18 60 1.94 1.90 120 1.92 180 Per Acre (%) 76 days 97 days 2.04 0.030 0.031 0.030 0.030 2.14 1.99 0.027 0.029 0.030 0.029 1.86 1.97 1.91 0.026 0.027 0.029 0.027 1.76 1.76 1.99 1.83 0;023 0.026 0.027 0.026 240 1.69 1.77 1.84 1.76 0.021 0.025 0.026 0.024 480 1.67 1.74 1.85 1.75 0.020 0.023 0.024 0.022 (.05) .19 ns ns ns ns ns ns ns (.01) .24 ns ns ns ns ns ns ns hsd 131 days Average 40 cent and tended to decrease# but not significantly so# with increasing amounts of applied K^O (Table 7). When all sampling dates were averaged# Ca in tubers was not affected by rates of applied K (Table 7). These data show that the concentration of calcium in potato petioles# leaves# and whole plants is 60 to 80 times that found in tubers# and is in agreement with the results of Laughlin (1966). 10. Magnesium Concentration in Potato Petioles No significant interaction between rate of applied K and potato variety was obtained with respect to Mg con­ centrations in potato tissue. Concentrations of Mg in all tissue are an average of both varieties. Magnesium content of petioles tended to increase as the plants matured. At each sampling date# Mg in the petioles decreased as the rate of K fertilizer was increased (Table 8) # although this decrease was not statistically significant at the early season sampling. 240 and 480 pounds of 1^0 decreased Application of (0.05 level) the Mg con­ centration in petioles at the midseason sampling as compared with those from the plots to which no K was applied. i TABLE 8 . — Magnesium content (%) in petioles and leaves in early season* midseason# and late season (56# 76# and 97 days after planting# respectively) as affected by rate of K fertilization Magnesium Content Pounds 1^0 Per Acre (%) Petioles Leaves 56 days 76 days 97 days 1.29 1.01 1.15 1.41 1.18 1.96 1.31 0.822 1.13 1.41 1.12 1.26 1.68 1.19 0.873 1.04 1.21 1.04 0.468 1.14 1.53 1.04 0.762 0.96 1.15 0.96 240 0.466 0.87 1.27 0.87 0.793 0.85 0.98 0.87 480 0.491 0.80 1.22 0.87 0.739 0.81 0.92 0.82 56 days 76 days 97 days 0 0.821 1.38 1.69 60 0.607 1.39 120 0.656 180 hsd Average Average (.05) ns .27 .55 .28 ns .14 .25 .15 (.01) ns .34 .69 ns ns .18 .32 .20 42 Magnesium content of the petioles at (97 days after planting) * decreased late season (0.01 level) when 240 and 480 pounds of K^O were applied ascompared to when no K was applied (Table 8). These results are in contrast Doll and Hossner (1964). that to those reported by Concentrations of Mg in potato petioles decreased with maturation of potato plants when grown on a Karlin loamy sand soil testing between 30 and 40 pounds of exchangeable Mg per acre. This may in part be attributed to the differences difference in the level of exchangeable Mg and/ thus; be merely a comparison of plants grown on a Mg-defieient as compared to a Mgsufficient soil. The McBride sandy loam soil contains more clay in the B horizon which might release Mg to the plants# while the clay content of the Karlin soil decreases with depth. When all sampling dates were averaged for each treatment the Mg concentration in petioles decreased sig­ nificantly when the 240 and 480 pounds of applied treatments were compared to the 60 pound ^ 0 treatments (Table 8) . and no K 43 11. Magnesium Concentration in Potato Leaves Concentration of Mg in potato leaves as affected by rate of applied K^O followed the same general pattern as in the petioles. At the early season sampling (56 days after planting) # Mg content of the leaves tended to de­ crease with increasing applications of K 0 although this decrease was not statistically significant. midseason (76 days after planting) (97 days after planting) For both the and the late season samplings# Mg concentration in the leaves of plants grown on plots to which 240 and 480 pound K_0 had been applied decreased (0.01 level) when compared to those to which no K had been applied (Table 8). The average leaf Mg content throughout the season was higher when no K# 60 or 120 pounds 1^0 had been applied than when 240 or 480 pounds of 1^0 were applied (Table 8). 12. Magnesium Concentration in Potato Plants In general# Mg concentration in whole plants# as in petioles and leaves# also tended to decrease as the rate of K was increased (Table 9). Magnesium content in plants TABLE 9-— Magnesium content (%) in plants and tubers in early tuber set, tubers, two-thirds to three-fourths mature, and mature tubers (76, 97, and 131 days after planting respectively) as affected by rates of K fertilization Magnesium Content Pounds 1^0 (%) Whole Plants Tubers 76 days 97 days 131 days 1.27 0.090 0.090 0.095 0.091 1.34 1.15 0.090 0.091 0.097 0.092 1.12 1.17 1.06 0.093 0.093 0.103 0.097 0.808 1.03 1.15 0.99 0.095 0.098 0.101 0.098 240 0.780 0.90 0.99 0.89 0.095 0.096 0.101 0.097 480 0.746 0.86 0.87 0.82 0.101 0.102 0.106 0.103 (.05) .127 .21 .24 .19 .009 .011 ns ns (.01) .218 .27 .31 .26 ns ns ns ns 76 days 97 days 131 days 0 1.050 1.31 1.41 60 0.938 1.19 120 0.911 180 Per Acre hsd Average Average 45 from treatments which received 240 or 480 pound K^O was significantly lower at all three sampling dates than those when no K# 60# or 120 pounds K 20 were applied (Table 9). The average Mg concentration in whole plants throughout the season was lower when 240# or 480 pound K^O was applied than when no K or 60 pounds I^O were applied (Table 9). 13. Magnesium Concentration in Potato Tubers A somewhat different pattern of Mg concentration in potato tubers as related to rate of applied 1^0 was ob­ tained. Although not always statistically significant# as rates of applied 1^0 were increased# the Mg concentration in tubers also tended to increase (Table 9). This is in contrast to the results found for the petioles# leaves and whole plants# but is in agreement with the results of Laughlin (1966). 14. Effect of Rates of Potassium on Reducing Sugar Content of Tubers at Harvest An important consideration involved in the produc­ tion of high quality potatoes is obtaining a tuber free of 46 degradation products and which will be resistant to nonenzymatic browning. Dehydrated and other forms of pro­ cessed potatoes should be prepared from raw materials that are relatively low in reducing sugar content if the prod­ uct is to be free from non-enzymatic discoloration when first produced and is to remain reasonably so in storage (Talburt and Smith, 1959) . No significant difference in reducing sugar content at harvest was found due to rates of applied K on Burbank and Sebago potato varieties (Table 10). TABLE 10.— Per cent reducing sugar in tubers on a fresh weight basis as related to rate of K fertilization Lbs. of K 2 O per acre Per cent Reducing Sugar Sebago Burbank 0 1.32 1.22 60 1.29 1.28 120 1.40 1.32 180 1.34 1.25 240 1.32 1.29 480 1.24 1.23 ns ns hsd (.05) 47 B. Source of Potassium Study 1. Yields and Specific Gravity of Burbank and Sebago Potatoes yields of both Burbank and Sebago potatoes were in­ creased by K fertilizers; however, yields were not affected by the source of K for the 1967 growing season (Tables 11 and 12). Similar results have been reported by Terman, 1950; Rowberry et a l ., 1963; and Murphy and Goven, 1966. TABLE 11.— Yield and specific gravity of Burbank and Sebago potatoes as affected by source of K fertilization Burbank Lbs. of K 2 O/A and source Yield Cwt/A Sebago Specific Gravity Yield Cwt/A Specific Gravity 150 1.091 214 1.088 150 KCl 184 1.089 245 1.087 150 K N 0 3 184 1.089 262 1.082 150 K nSO„ 2 4 197 1.089 237 1.088 150 K 2C 0 3 161 1.089 241 1.088 hsd (.05) ns 0 ns ns .004 48 TABLE 12.— Significant differences between Burbank and Sebago potato yields as affected by source of K fertil­ ization Probability Level Comparison KC1 vs. KN03 V ° 4 VS • K 2C03 KC1 and KNO, vs. K,S04 and K COj Sebago in o• No K vs. K sources Burbank .05 ns ns ns ns ns ns The specific gravity of the Sebago variety was lower when KNO^ was used as a source of K than when the other K fertilizers was applied (Table 11). The specific gravity of Russet Burbank potatoes was not affected by the source of K fertilizer. 2. Potassium Concentration in Potato Petioles No significant interaction between K source treat­ ments and potato variety was noted with respect to K con­ centrations in potato leaves and petioles# so the data presented are on average concentration of K for both v a r ­ ieties . 49 Concentration of K in petioles tended to be highest at the early season sampling and decreased as the plants matured (Table 13)„ planting) At the early season (62 days after and midseason sampling (83 days after planting) # the concentration of K in the petioles was higher when K was applied#'regardless of the source# applied: than when no K was concentrations of K in petioles were higher when KC1 and K 2 C 0 3 were applied than when KNO^ or K^SO^ were applied (Table 13) . The K content in petioles was less at midseason and late season when K^SO^ was applied. The average K content throughout the season was higher in petioles from plants grown on plots to which K was applied than in those to which no K was applied (Table 13). 3. Potassium Concentration in Potato Leaves Potassium concentration in potato leaves was higher early in the season and decreased as the plants matured (Table 13) . season The concentration of K in the leaves at early (62 days after planting) increased when K was applied# although this increase was not statistically significant (Table 13) . The content of K in the leaves at midseason TABLE 13.— Potassium content (%) in petioles and leaves at early season# midseason# and late season (62# 83# and 104 days after planting# respectively) as affected by source of K fertilization Treatment Lbs. of K 2 O/A and source Potassium Content Petioles Leaves 62 days 83 days 104 days 5.99 4.44 2.16 1.81 2.80 5.15 7.69 4.75 2.54 2.29 3.19 7.37 5.19 7.44 4.83 2.70 2.34 3.29 9.78 6.83 4.71 7.10 4.78 2.62 2.18 3.19 10.34 7.64 6.71 8.03 4.85 2.89 2.76 3.15 (.05) .72 .61 .71 .34 ns .18 .38 .23 (.01) .93 .79 .93 .49 ns .24 .50 .27 62 days 83 days 104 days 8.66 5.92 3.40 10.63 7.29 150 KNC>3 9.77 150 K.SO. 2 4 150 K 2C 0 3 0 150 KC1 hsd (%) Average Average 51 (83 days after planting) for all K treatments was higher than for the no K treatment. petioles# As in the case of the the concentration of K in the leaves when K 2 S 0 4 was applied was lower than when K^CO^ was applied at mid­ season and late season (Table 13). The average K content at all sampling dates increased in leaves on plants grown on plots to which K had been applied as compared to those which did not receive K (Table 13). The concentration of K in both petioles and leaves on plants grown on plots to which was applied was lower throughout the growing season than to those to which K^CO^ was applied. This is in agreement with results re­ ported b y Younts and Musgrave of this experiment# (1958). Under the conditions it is difficult to explain the reason for a high K uptake from the K 2C03 source and lower yield response for the Burbank potato variety (Table 13). It is suggested that more work needs to be done with this source of K before a reasonable conclusion can be drawn. 4. Calcium Concentration in Potato Petioles NO significant interaction between K source treat­ ments and potato variety was obtained with respect to Ca 52 content in potato petioles and leaves# so the data pre­ sented are an average of both varieties. Calcium concentration increased in petioles as the potato plant matured. At the early season sampling (62 days after planting) # the Ca content decreased in petioles from plants grown on plots to which K 2C 0 3 was aPPlie<^ as compared to those to which no K was applied (Table 14). The concentration of Ca in the petioles was not affected by source of K for the midseason or late season samplings (Table 14)# nor were the average Ca concentrations for those samplings. 5. Calcium Concentration in Potato Leaves For the early season sampling the Ca content of potato leaves was less when K was applied (Table 14). was applied than when no The Ca content in potato leaves was not significantly affected by various sources of K at the midseason or late season samplings (Table 14). TABLE 14.— Calcium content {%) in petioles and leaves at early season, midseason# and late season (62, 83, and 104 days after planting, respectively) as affected by source of K fertilization Treatments Lbs. of K 20/A and source Calcium Content Petioles Leaves 62 days 83 days 104 days 1.22 1.39 1.49 2.19 1.6-9 1.40 1.16 1.27 1.36 2.07 1.56 1.11 1.31 1.12 1.20 1.35 1.98 1.51 0.91 1.22 1.43 1.18. 1.25 1.51 2.15 1.63 0.85 1.14 1.39 1.12 1.16 1.33 1.99 1.49 (.05) .12 ns ns ns .17 ns ns ns (.01) .16 ns ns ns .23 ns ns ns 62 days 83 days 104 days 1.06 1.23 1.38 150 KC1 0.94 1.16 150 K N 0 3 0.94 150 K 2S04 150 K 2C 0 3 0 hsd (%) Average Average 54 6. Magnesium Concentration in Potato Petioles No significant interactions between K treatments and variety were noted with respect to Mg content in po­ tato tissue and the data presented are an average of both varieties „ The Mg content in potato petioles increased with maturation (Table 15). At the early season sampling (62 days after planting)# Mg content in petioles was less when KC1# K N O ^ » and plied. were applied than when no K was ap­ K 2S 0 4 The Mg content of petioles was lower when or K^SO^ were applied (0.01 and 0.05 level# respectively) than when no K» KC1# or KNO^ were applied At midseason (Table 15). (83 days after planting) the Mg in petioles was lower when K 2C03 # KC1 or KN03 were applied than when no K was applied. At late season (104 days after planting)# the Mg content was lower in petioles from plots to which K 2C 0 3 0.05 level# respectively) was applied (Table 15). (0.01 level) or K 2 S 0 4 were applied (0.01 and than from those to which no K The average Mg content was lower in petioles of plants grown on plots to which K 2CC>3 was applied than in those from any of the other treatments (Table 15) . TABLE 15.— Magnesium content {%) in petioles and leaves at early season* midseason* and late season (62* 83, and 104 days after planting, respectively) as affected by source of K fertilization Treatments Lbs. of K 2 O/A and source Magnesium Content Petioles 62 days 83 days 0.842 1.020 1.59 150 KC1 0.693 0.876 150 KN03 0.716 150 K-SO. 2 4 150 K 2C03 hsd Leaves 62 days 83 days 104 days 1.15 0.880 0.933 1.16 0.99 1.39 0.98 0.790 0.830 1.02 0.87 0.818 1.38 0.97 0.831 0.860 1.02 0.90 0.663 0.942 1.50 1.03 0.782 0.897 1.06 0.91 0.535 0.736 1.21 0.82 0.718 0.800 0.91 0.80 (.05) .114 .132 .266 .12 .097 .092 .13 .08 (.01) .147 .171 .345 .21 .126 .119 .17 .10 0 104 days (%) Average Average 56 7. Magnesium Concentration in Potato Leaves Leaf concentration of Mg increased as potato plants matured (Table 15). Early season/ midseason/ and late season sampling data show that the Mg content was lower in leaves from plots to which K 2C 0 3 or K 2S04 were applied (0.01 and 0.05 level/ respectively) which no K was applied (Table 15). than from those to Magnesium content of potato leaves was not significantly different between KC1/ KNO / and K S O . . J A The average Mg content was lower in T 1 leaves from plants grown on plots to which K 2 C 0 3 was aP" plied than in those to which no Kz KNO^ or K 2S04 were applied (Table 15) . 8. Effects of Sources of Potassium on Reducing Sugar Content of Tubers at Harvest No significant differences in reducing sugar con­ tent at harvest was found due to sources of applied potas­ s i u m for Burbank and Sebago potato varieties (Table 16). These results/ together with these from the rate of K experiment/ suggest that the reducing sugar content is 57 more likely to be affected by storage conditions after harvest. TABLE 16.— Per cent reducing sugar in tubers on a fresh weight basis as related to source of K fertilization Lbs. of K 20/A and source Per cent Reducing Sugar Sebago Burbank 1.39 1.29 150 KCl 1.43 1.31 150 1.53 1.28 1.58 1.32 1.42 1.27 ns ns 0 150 150 kno3 K 2S04 K 2C°3 hsd ( .05) C. General Discussion of Potassium Rate and Source Experiments The yield decreases noted when heavy rates of KC1 were applied may be due to a K-induced Mg deficiency. Since Mg is a structural constituent of the chlorophyll molecule and is an activator of many enzyme reactions 58 involving phosphate transfer and carbohydrates metabolism, inadequate Mg would result in decreased yields. The reason for the depression of Mg uptake is difficult to explain. An increased K activity in soil solution possibly resulted in an interaction with the carrier that combines with the Mg ion or in an interac­ tion with the carrier-producing system so that less Mg carrier is produced. Another possibility is that an in­ crease in soil K results in a lowering of the activity or availability of Mg in the soil. A partial collapsing of the plates of expanding lattice clays could result from high applications of K, and Mg could be trapped in inac­ cessible interlayer positions in the clay minerals. The lower Mg content of potato tissue grown on plots to which was applied as compared to other K sources cannot be explained on the basis of data obtained in the experiments reported herein. The reducing sugar content of tubers at harvest was not affected by rate or source of K. Applications of more than 120 pounds K^O per acre probably resulted in some degree of luxury consumption and was uneconomical with respect to both yields and initial 59 cost of fertilizer. However# critical levels for elements shift as cation contents vary and should make one further aware that we are dealing with 16 or more elements in a plant that are simultaneously interacting. This is an important fact# because unless liming and fertilizer pro­ grams are cafefully evaluated and monitored# nutrient ex­ cesses may cause shiifts in the requirements for other elements. PART II EVALUATION OF POTASSIUM QUANTITY-INTENSITY RELATIONSHIPS OF SELECTED MICHIGAN SOILS LITERATURE REVIEW Potassium Release and Fixation Potassium/ like most other plant nutrients in soils/ exists in forms which range from the water-soluble to the extremely inaccessible (Volk# 1933). In many partially-weathered soils/ the clay and silt fractions cannot merely be regarded as colloidal frameworks on which cation exchange reactions take place (Arnold# 1960). An understanding of the behavior of lattice K is as im­ portant as the understanding of the behavior of the readily exchangeable K (Arnold# 1960) . In soils that are not strongly weathered# feld­ spars and micas ordinarily are the most abundant of the K-bearing minerals (Reitemeier# 1951). The most important of these are orthoclase and microcline feldspar# biotite and muscovite# mica and illite (Marshall# 1964). Potassium feldspars are silicates consisting of SiO^ and AlO^ tetrahedra linked in all directions through the oxygen of the tetrahedra (Rich# 1968). 61 Potassium in 62 the K-feldspars is held in the interstices of the Si# Al-0 framework and the negative charge produced b y A1 3+ in tetrahedral coordination is balanced by the positive charge of the cations in the interstices (Rich# 1968). Extensive experiments on weathering of feldspars were conducted by Correns (1963) . Water and weak acids initially released K from K-feldspar at a more rapid rate than other constituents# but in the course of weathering a Si-Al-0 residue layer developed about the particles and reduced the rate of K loss to that of the decomposition rate of the Si-Al-0 layer. Correns visualized a complex reaction and suggested that A1 3+ is the ion which counters the negative charge produced b y loss of K + to the solution phase. Feldspars occur mostly in the sand and silt frac­ tions of soil and are either absent from or occur only in traces in the clay fraction (Reitemeier# 1951) . (1966) Black states that the "stability of feldspars is asso­ ciated with relative large particle diameter# as would be expected from the resistant residual surface layers." Micas consist of unit layers each composed of two Si# Al-0 tetrahedral sheets between which is a M-0# OH octahedral sheet# where M consists of A1 3+ » Fe 2+ # Fe 3+ # Mg 2+ # and other cations (Rich# 1968) . Micas are classi­ fied in two major groups# dioctahedral and trioctahedral (Arnold# 1960) . In muscovite# a member of the dioctahe­ dral group# two out of three octahedral cation positions are occupied# whereas in biotite a member of trioctahedral mica# all three positions are occupied (Rich# 1968). octahedral coordination in dioctahedral minerals A1 the principal cation# whereas the divalent ions Mg Fe 2+ In 3+ 2+ is and are the main cations in the trioctahedral minerals (Rich# 1968). Potassium ions occupy positions between the unit layers in facing ditrigonal holes and are vulnerable to release when weathering occurs (Arnold# 1960). Illite is considered to be a mixed-layer micamontmorillonite (or vermiculite). Rich (1968) states that the "mixing may be in the XY plane as well as in the Z direction# however# the latter type of interstratifica­ tion is usually recognized as the normal structure of mixed layer minerals." Under conditions of free drainage# biotite weathers more easily than muscovite (Arnold# 1960) and there is clear evidence that the K in biotite is much more acces­ sible to plants than the K in muscovite (Mortland et al.# 64 1956). The studies of Walker (1949) and Denison et al. (1929) established that the weathering of micas depends on the replacement of some interlayer K b y K^O molecules * or# as is now thought# by hydronium ions# to give the mineral hydrobiotite. On weathering# changes within the silicate layers take place such as oxidation of ferrous iron# the preferential loss of some ions and# possibly# conversion of some oxygen ions to OH groups# which d e ­ crease the net negative charge on the lattice (Rich# 1968). Some soils can provide enough K for many years# but the rate of release in others is too slow to meet the immediate needs of crops gories of K in soils (Reitemeier# (Mortland# by such names as "native#" 1951). The cate­ 1961) have been described "nonexchangeable#" "fixed#" "lattice#" "exchangeable#" and "soil solution" K. Mort­ land states that most of these categories of soil K are derived empirically, in that each is frequently de­ fined according to. the particular procedure used for its analysis and may give little in­ dication of the dynamics of K in a given soil. A study of the release of native and fixed K in soils was made b y Reitemeier et al. (1951) . The mineral composition of various fractions of the soil was included# 65 and no obvious relationship was noted between the extent of K release and the content of hydrous mica. They also pointed out that the role of K minerals must depend not only on their total abundance but also on their present K content and stages of weathering or formation. In their study» the two soils that had the highest rate of K re­ lease also had the highest montmorillonite content. Since the clay fraction of all the soils except one studied by Reitemeier et al. had more than 60% hydrous mica 1968) (Rich/ pointed out that a combination of a good source of K (such as a fine-grained mica) and a mineral with a high cation exchange capacity and a low fixing capacity# might be necessary for the maintenance of an adequate exchange­ able K supply. A high exchangeable K level may not be necessary if K released from a nonexchangeable to an ex­ changeable form is rapid enough (Rich# 1968). The rate of release of initially nonexchangeable K thus becomes a matter of critical importance (Rich# 1968). The rate of K release from micas and of "fixed" K from vermiculite has been reported to be a diffusion-controlled process (Ellis and Mortland# Mortland and Ellis# 1959). 1956; Mortland# 1958; and If the rate of release of K from an unavailable to an available form is diffusioncontrolled » then this process is more dependent upon diffusion processes than upon the law of mass action (Walker, 1959). Mortland (1961) used the following equation to express the rate of release of "fixed" K from vermiculite and "native" K from biotite: r = B (C1 - C) where r is the rate of K release; the activity of K in the lattice; C, the activity of K in solution; and B, the diffusion velocity constant* which contains geometry factors of the diffusion zone and the diffusion coeffi­ cient. From this equation it can be observed that if C^ is greater than C, release occurs. If, however, C is greater than C^, the opposite process, of fixation, will occur and r will represent the rate of fixation. Mortland points out in a soil with a heterogeneous group of 2:1 clay minerals, it is possible for both release and fixa­ tion to be taking place at the same time. If a soil is not at equilibrium, K may be released from one micaceous form and fixed by another. 67 In terms of the equation used by Mortland (1961) # the rate at which K is either fixed or released from any specific mineral is determined by the constants B and and the variable C. The constants B and C 1 may be con­ sidered as characteristic properties of a given mineral that determine# to a large degree# the dynamics of its K reactions. Measurement of Potassium Potential and Buffering Capacity and Their Relation to the Supply of Potassium to Plants Scheffer and Ulrich (1962) have suggested that the activity ratio aK/a (Ca + M g ) # or ARK # in a solu© tion in equilibrium with a soil provides a satisfactory measure of the availability or the potential of soil K. |{ ARg is a measure of the intensity of labile K (K ions capable of exchange within 30 minutes at 25°C with Ca or Mg ions in dilute solution) in the soil. Different soils exhibiting the same value of AR^ may not possess the same K capacity for maintaining A R q while K is removed by plant roots (Beckett# 1964a; Schofield^ 1947). When describing the K status of a soil it is desirable to specify not only 68 the current potential of K in the labile pool but also the form of the quantity-intensity relation (Q/l rela­ tion) or the way in which the potential depends upon the quantity of labile K present (Beckett/ 1964a). Despite the fundamental nature of these concepts/ there are certain difficulties in their use# as discussed by Beckett (1964a/ b ) . The total activity (Low/ 1951) and electrochemical potential of an ion throughout the soil solution system is not a constant for the soil/ but de­ pends on the total concentration of the solution. The chemical potential of the ion on the solid phase may be assumed to be constant/ but this quantity cannot b e mea­ sured/ so Beckett (1964a) has suggested the adoption of activity ratios as a measure of the difference between the chemical potentials of two different ion species on the soil. As the K potential near a root is reduced/ K ions diffuse toward it, under many conditions quite slowly/ at a rate depending on the local inequality in K potential (Beckett/ 1964b). i Potassium at a high activity in an u n ­ depleted soil is carried b y the flow of water to the root and reducing the potential of the labile K causes the 69 release of K from "fixed" forms# often slowly# but at a rate proportional to the difference between the reduced potential and the normal equilibrium potential for the soil (Mathews and Beckett# 1962). Mortland et al. (1956) have also shown root exudates accelerate the decomposi­ tion of unweathered K-bearing minerals. Tinker (1964) states "there is no fully satisfac­ tory reason for assuming the availability of K to plants depends on the chemical potential." Nevertheless# the chemical potential of an ion on the soil must control the potential of the ion on the plant root exchange sites# and it seems likely that the chemical potential is a major factor in root uptake. Alternatively# the important quality may be the activity of the ion in the soil solution# for some recent work further substantiates the concept that ion uptake by plant roots is from the soil solution and not directly from the solid phase of the soil 1960). (Lagerwerff# The variability of this quantity with solution concentration is then overcome by relating it to the equiv­ alent value for another ion (Tinker# 1964). Beckett (1964b) has shown that (Ca + Mg) can con­ veniently be employed as the denominator in measuring the 70 ratio in a single soil. Woodruff (1955a# b# c) has sug­ gested that the function controlling K uptake is the exchange energy, given by AG° =* -RT In (K)/(Ca + Mg) For corn and soybeans# Woodruff (1955c) 1/2 set the energy of replacement of K at which deficiencies appeared at -4,000 calories per' chemical equivalent# and suggested an upper limit of -3,000 calories per chemical equivalent for normal performance. Arnold (1962) has applied Woodruff's methods to a variety of British soils# and obtained good correla­ tions between exchange energies and uptake of K by rye­ grass in pots during short-term cropping. The activity ratio aR/a (Ca + M g ) ^ ^ # or ARK # of a 6 solution in equilibrium with a soil is taken to be a m e a ­ sure of the K intensity (I ) . It measures the chemical po- lv tential of the labile K present# potential of labile 1964a). (Ca + Mg) relative to the chemical in the same soil (Beckett# The quantity of exchangeable K(Q ) is diffiIN cult to define or measure relative to a state of the soil with no labile K present# because of the K held at "specific sites" (Beckett and Nafady# 1967) # which gives the Q/l relation its asymptotic form at low values of AR. The form of the Q/l relation has a linear upper part and 71 a curved lower part. Beckett (1964a) has shown that the curvature at low values of AR is not an artefact due to the experimental technique, nor was it due to the release of fixed K during the experiment. The asymptotic conver­ gence of the Q/l relation to the Q-axis is one reason why determinations of exchangeable K(Q K or AK) are sometimes not precise. A graph of AK against AR has the same form as a graph of Q against AR and avoids the difficulties of meaX\ suring Q K (Beckett and Nafady, 1967). The A K must be estimated as the difference between the K concentrations of a solution before and after the addition of soil (Beckett, 1964a). METHODS AND MATERIALS A. Greenhouse Procedures Sixteen soils , from 13 soil series which had a considerable range in K content were selected from dif­ ferent locations in Michigan. Extractable nutrient con­ tent and pH (Table 17) were determined as in Part I of this Thesis. A greenhouse experiment was laid out in a random­ ized complete block design with four replications. One- gallon galvanized cans lined with plastic bags were used as containers. through an 8 Soil samples were air-dried and passed -mesh sieve. Three thousand grams of well- mixed soil was placed in each container. ing# 150 ppm phosphorus ganese (P) as Ca(H 2 P04)2 # (Mn) as MnSO^* 4 ppm zinc ppm nitrogen Prior to seed­ (Zn) 6 ppm of m a n ­ as ZnSO^# and 150 (N) as Ca(N0 3 ) 2 were mixed thoroughly with the soil in each pot. Thirty oat seeds were planted in each pot at a depth of 1/2 inch and thinned to a uniform number of 72 TABLE 17.— Extractable cations and pH prior to cropping for 16 Michigan soils used in greenhouse and laboratory evaluations Extractable-*- cations (meg / 1 0 0 g.) Soil Type PH K 1 . Charity clay loam I . 3. 4. 5. 2 6 . 7. 8 . 9. 1 0 . 1 1 . 1 2 . 13. 14. 15. 16. Charity clay loam II Lenawee clay loam Sims clay loam I Sims clay loam II Sims clay loam III Colwood loam Conover loam Miami loam Hettinger silty clay loam Brimley silt loam Breckenridge sandy loam Hillsdale sandy loam Hodunk sandy loam McBride sandy loam Metamora sandy loam 0.439 0.479 0.203 0.908 0.271 0.156 0.330 0.241 0.203 0.290 0.156 0.165 0.156 0.232 0.271 0.339 ^"Extracted with 1 N NH.OAc for 10 minutes. — 4 Ca 20.33 22.12 14.04 16.50 15.84 9.77 15.84 11.91 11.22 16.55 10.14 13.68 9.77 3.64 2.67 4.01 - Mg 1.56 1.69 3.15 4.22 3.96 1.56 4.23 2.05 1.25 4.02 1.80 2.68 1.56 1.04 0.77 0.42 7.7 7.5 6.9 6.5 7.3 7.6 7.5 7.1 7.2 7.3 7.5 7.4 7.6 6.3 6.5 6.2 74 plants per pot 10-12 days after emergence. The oat plants were harvested when the inflorescence was beginning to emerge from the sheath. The harvested tissue was dried at 65°C# weighed# ground to pass a 20-mesh sieve# and saved for chemical analysis. Oat tissue was ashed and analyzed for K content as outlined in Part I of this Thesis. Four crops of oats were grown# and prior to each seeding# 100 g. of soil was removed after the soil in the pots had been removed# screened# and well-mixed. 100 The g. soil samples were allowed to air day prior to d e ­ termining the exchangeable K. kept moist between seedings. were February 6 The soil in the pots was Planting dates for each crop , March 28, April 29# and June 12, 1968. B. Soil Potassium Evaluations Equilibrium solution concentrations of K, Ca, and Mg were determined as given by Beckett (1964a and 1964b). For each soil, duplicate 5 g. samples were equilibrated with 50 ml 0.00159M C a C ^ KCl. containing different amounts of The amounts of KCl used in the equilibrating solutions 75 were 0, 0.00023, 0.00071, 0.00143, and 0.00181 M/L. were kept at constant temperature and in this period received 8 (25 ± 1°C) Samples for 24 hours hours of shaking. After settling, 25 ml of the supernatant solution were removed. Potassium was determined on a Coleman Model 21 flame photo­ meter; Mg and Ca on a Perkin Elmer Model 290 and 303 atomic absorption spectrophotometer respectively using 1500 ppm La to supress interfering ions (Doll and Christenson, 1966). Activity ratios were calculated from the composition of supernatant solutions and activity coefficients deter­ mined according to the Davies modifications of the DebyeHuckel equation (Butler, 1964). For an ion of charge Z, either positive or negative, the activity coefficient (7 ) of the ion is given by - lo91 0 7 = 0-5091 Z 2 ( r ^ - The constants apply to solutions at 25°C. 0.2 l). The ionic strength (I) of the solution is given by 2 I = 1/2 2 Ci Z i where ci is the concentration of the ith ion, Zi is its charge and the summation extends over the ions in the solutions. 76 The gain or loss of K (AKe) by the soils was ob­ tained by subtracting the K concentrations of the solution before and after equilibration. The quantity-intensity (Q/I) relation for each soil was determined by plotting AKe against the corresponding AR value. The activity ratio at equilibrium (ARe ) was obtained from the intersection of the Q/I curve with the AK = 0 axis. represents the ratio aK ^ ( C a + M g ) ^ ^ K (AR ) © The in a solution that upon admixture with soil maintains its numerical value with respect to the activity of K, Ca, and Mg. The exchangeable K (-AK), values were determined V by extending the linear part of the curve to the AR line. = 0 Potential buffering capacity (PBC ) was calculated K as the slope of the Q/I curve or -AK/ARe . RESULTS AND DISCUSSION The capacity of soils to supply K to plants depends not only on the quantities of the different forms present, but also on the rate at which nonexchangeable K is released to an available form. In soils, an equilibrium exists b e ­ tween exchangeable and nonexchangeable K, so that nonex­ changeable K is released at a low level of exchangeable K, while at high levels, exchangeable K is "fixed" in a nonex­ changeable form. 1. Yields and Potassium Uptake by Oats Yields of the first oat crop were quite similar on all the various soils (Table 18) except Hodunk. The low yields and low K-uptake from the Hodunk soil are due to a residual herbicidal effect. However, large differences in K-uptake (Table 19) were obtained between the other soils for the first crop; for example, oats grown on some soils contained at least twice as much K as those grown on other soils (Table 19). About two weeks after planting the second crop, oats grown on Sims II, Miami, Brimley, 77 Breckenridge, and TABLE 18.— Yields of four oat crops grown in greenhouse on sixteen Michigan soils without added potassium Grams Dry Weight Per Pot Soil Type Crop 1 . 2 . 3. 4. 5. 6 . 7. 8 . 9. 1 0 . 1 1 . 1 2 . 13. 14. 15. 16. 1 Charity clay loam I Charity clay loam II Lenawee clay loam Sims clay loam I Sims clay loam II Sims clay loam III Colwood loam Conover loam Miami loam Hettinger silty clay loam Brimley silt loam Breckenridge sandy loam Hillsdale sandy loam Hodunk sandy loam McBride sandy loam Metamora sandy loam 6.29 6.84 7.06 7.81 7.26 6.82 7.56 6.12 6.50 7.86 7.64 7.45 7.27 1.84 7.12 7.35 Crop 2 7.33 7.92 7.04 10.19 8.12 6.23 8.88 8.17 6.42 8.98 7.04 6.89 5.48 5.93 6.61 7.96 Crop 3 Crop 4 Total 7.40 8.75 7.90 9.95 8.34 5.53 9.09 6.62 6.80 8.70 5.07 5.94 3.67 6.71 4.83 5.91 4.69 4.50 4.57 7.35 3.10 3.20 5.10 3.61 3.42 4.49 2.72 3.36 1.70 3.58 2.08 2.17 25.71 28.01 26.57 35.30 26.82 21.78 30.63 24.07 23.14 30.03 22.47 23.64 18.12 18.06 20.64 23.39 TABLE 19c— Potassium uptake by each of four crops and the total uptake b y oats grown in greenhouse on sixteen Michigan soils without added potassium Potassium Removed meg/100 g. soil Soil Type . 2 . 3. 4. 5. 6 c 7. 8 c 9. 1 0 . 1 1 . 1 2 . 13. 14. 15. 16. 1 Charity clay loam I Charity clay loam II Lenawee clay loam Sims clay loam I Sims clay loam II Sims clay loam III Colwood loam Conover loam Miami loam Hettinger silty clay loam Brimley silt loam Breckenridge sandy loam Hillsdale sandy loam Hodunk sandy loam McBride sandy loam Metamora sandy loam Crop 1 Crop 2 Crop 3 . Crop 4 Total 0.246 0.278 0.129 0.369 0.184 0.108 0.198 0.126 0.108 0.231 0.084 0.118 0.075 0.062 0.164 . 0.187 0.144 0.195 0.087 0.395 0.113 0.040 0.160 0.094 0.116 0.086 0.061 0.082 0.047 0.224 0.025 0.545 0.671 0.349 1.189 0.395 0.020 0.200 0.062 0.032 0.029 0.044 0.017 0.027 0.016 0.029 0.015 0.528 0.302 0.256 0.466 0.186 0.240 0.158 0.279 0.301 0.380 0.100 0.073 0.103 0.051 0.050 0.040 0.126 0.086 0.111 0.201 0.073 0.032 0.108 0.044 0.046 0.088 0.034 0.045 0.027 0.062 0.036 0.060 0.022 80 Hillsdale soils showed moderate K deficiency symptoms; both yields and uptake of K were decreased when compared to the other soils (Tables 18 and 19). Yields of the second oat crop were higher than those of the first crop on the Charity I, Charity II, Sims I, Sims II, Colwood, Conover, and' Hettinger soils. The higher yields are prob­ ably due to both more total hours of higher light inten­ sity and higher K supplying power (Table 19). Yields of the third crop generally decreased as compared to the second crop (Table 18), except on Charity I, Charity II, Lenawee, Sims I, Sims II, Colwood, and Het­ tinger soils. Comparable yields for the second and third crop on these seven soils can be attributed to the high clay content and the capacity of these soils to maintain higher levels of exchangeable K. Severe K deficiency symptoms were observed at early growth stage on oats grown on Sims III, Conover, Miami, Brimley, Breckenridge, Hills­ dale, Hodunk, McBride, and Metamora soils, from none of which was more than 0.075 meg. K/100 g. soil removed by the oats (Table 19). Severe K deficiency symptoms were noted in the fourth crop of oats grown on all soils except Sims clay 81 loam I. Yields of the fourth crop were frequently only one half those of the third crop (Table 18). This yield decrease can be attributed to severe stress on the Ksupplying capacity of the soils due to intensive cropping (Table 19). 2. Uptake of Exchangeable and Nonexchanqeable Potassium by Oats Exchangeable K, as measured by 1 N NH^OAc, prior to cropping was significantly correlated (r = +0.98***) with total uptake of K; with uptake of nonexchangeable K (r = +0.82***) by four oat crops and with the K-uptake by each oat crop (Table 20). This correlation was noted de­ spite wide variations in the extent to which initial ex­ changeable K in the soils represented a source of K for the oats (Table 21). For example, exchangeable K (mea­ sured as the difference between exchangeable K prior to cropping and that after the fourth crop) comprised 77 per cent of the total K-uptake on the McBride soil, but only 26 per cent in Sims H a n d Hettinger soils (Table 21), with the remaining K taken up by the plants being derived from nonexchangeable fo r m s . The amount of exchangeable K in the 82 TABLE 20.— Correlation between exchangeable potassium prior to cropping; uptake of potassium and yields of four crops of oats grown in greenhouse on 16 Michigan soils Measurement DF r Total K-uptake by oats K-uptake by crop 1 K-uptake by crop 2 K-uptake b y crop 3 K-uptake b y crop 4 Nonexchangeable K-uptake by oats Total yield of oats 14 14 14 14 14 14 14 0.98*** 0 .9 7 *** 0.96*** 0.92*** 0.94*** 0.82*** 0.74** **Significant at 0.01 level. ***Significant at 0.001 level. McBride soil represented the major portion of plantavailable K, whereas in the Sims and Hettinger soils a considerable portion of the plant-available K was present in a nonexchangeable form. Potassium released from nonexchangeable form dur­ ing cropping (Table 21) accounted for over 50 per cent of the K taken up by oats on all soils except Hodunk, McBride, and Metamora. At least 0.10 meg, K / 1 00 g. soil (equivalent to 78 pounds/acre) was released to the first oat crop (Table 22) from Charity I, Charity II, Sims I, Sims II, Colwood, and Hettinger soils. This is in part reflected by the high levels of exchangeable K in these soils prior to the second cropping (Table 23). TABLE 21c— Uptake of exchangeable and nonexchangeable potassium b y four crops of oats grown in greenhouse on 16 Michigan soils Uptake of Potassium in Soil Soil Type . 2 . 3. 4. 5. 1 6. 7. . 9. 1 0 . 1 1 . 1 2 . 13. 14. 15. 16. 8 Charity clay loam I Charity clay loam II Lenawee clay loam Sims clay loam I Sims clay loam II Sims clay loam III Colwood loam • Conover loam Miami loam Hettinger silty clay loam Brimley silt loam Breckenridge sandy loam Hillsdale sandy loam Hodunk sandy loam McBride sandy loam Metamora sandy loam Ex­ change­ able 0.265 0.274 0.091 0 c560 0.102 0.074 0.228 0.139 0.111 0.122 0.077 0.093 0.067 0.180 0.232 0.288 % of Total K Uptake 49 41 26 47 26 37 43 46 43 26 41 38 42 64 77 76 (meq / 1 0 0 g.) Nonex­ change­ able % of -Total K Uptake 0.265 0.397 0.258 0.629 0.293 0.126 0.300 0.163 0.145 0.344 0.109 0.147 0.081 0.099 0.069 0.092 51 59 74 53 74 63 57 54 57 74 59 62 58 36 23 24 0.545 0.671 0.349 1.189 0.395 0.200 1 ^Extracted with 1 N NH.OAc for 10 minutes. 2 4 Extimated uptake of nonexchangeable K = uptake of K by oats— (exchangeable K prior lto cropping— exchangeable K after cropping). ~ Total 0.528 0.303 0.256 0.466 0.186 0.240 0.158 0.279 0.301 0.380 TABLE 22.— Nonexchangeable potassium taken up by each oat crop and total uptake of nonexchangeable potassium Nonexchangeable 1 K-Uptake megyiOO g. soil Soil Type Charity clay loam I Charity clay loam II Lenawee clay loam Sims clay loam I Sims clay loam II Sims clay loam III Colwood loam Conover loam Miami loam Hettinger silty clay loam Brimley silt loam Breckenridge sandy loam Hillsdale sandy loam Hodunk sandy loam McBride sandy loam Metamora sandy loam Crop 2 Crop 3 Crop 4 Total 0.116 0.137 0.082 0.130 0.174 0.059 0.076 0.118 0.068 0.175 0.084 0.024 0.051 0.077 0.067 0.120 CN © i— 1 0 o . 2 . 3o 4. 5c 6 . 7. 8 . 9. 1 0 . 1 1 . 1 2 . 13. 14. 15. 16. 1 Crop 1 0.058 0.043 0.170 0.037 0.099 0.045 0.046 0.065 0.033 0.013 0.031 0.013 0.018 0.037 0.032 0.065 0.041 0.213 0.019 0.019 0.008 0.025 0.265 0.397 0.258 0.629 0.293 0.126 0.300 0.163 0.145 0.344 0.109 0.147 0.081 0.099 0.069 0.092 0.020 0.005 0.011 0.002 0.111 0.016 0.024 0.070 0.035 0.036 0.076 0.025 0.016 0.018 0.053 0.032 0.031 0.021 0.034 0.014 0.019 0.012 0.028 0.008 0.019 ^"Estimated uptake of nonexchangeable K = uptake of K by oats - (exchangeable K prior to cropping - exchangeable K after cropping). TABLE 23^— Exchangeable potassium in 16 Michigan soils before and after four oat crops were grown in the greenhouse Exchangeable 1 K(meg / 1 0 0 g= soil) Soil Type Prior to Crop 1 . 2 . 3. 4c 5. 6 c 7. 8 . 9. 10 c 1 1 c 1 2 . 13c 14. 15. 16. 1 Charity clay loam I Charity clay loam II Lenawee clay loam Sims clay loam I Sims clay loam II Sims clay loam III Colwood loam Conover loam Miami loam Hettinger silty clay loam Brimley silt loam Breckenridge sandy loam Hillsdale sandy loam Hodunk sandy loam McBride sandy loam Metamora sandy loam 0 «439 0.479 0 c203 0.908 0.271 0c(L56 . 0 o330 0.241 0.203 0.290 0.156 0.165 0.118 0.232 0.271 0.339 ^Extracted with 1 N NH^OAc for 10 minutes. — 4 Prior to Crop 2 0.309 0.338 0.156 0.669 0.261 0.109 0.252 0.175 0.137 0.232 0.109 0.146 0.063 0.175 0.118 0.137 Prior to Crop 3 Prior to Crop 4 0.241 0.261 0.137 0.449 0.232 0.091 0.194 0.118 0.203 0.118 0.359 0.175 0.082 0.156 0.109 0.110 0.100 0.194 0.091 0.109 0.054 0.063 0.054 0.063 0.168 0.082 0.222 0.100 0.045 0.062 0.050 0.054 After Crop 4 0.174 0.205 0.112 0.348 0.169 0.080 0.102 0.102 0.092 0.156 0.079 0.072 0.041 0.052 0.041 0.051 86 The Charity II, Sims I, and Colwood soils were the only soils from which 0.1 meq K/100 g. soil or more was re­ leased during the second cropping (Table 22). The contribution of nonexchangeable K to the third crop from the Charity I, Charity II, Lenawee, Sims I, Col­ wood, and Hettinger soils was considerably more than from the other ten soils, but the release of nonexchangeable K from Sims clay loam I was much larger (Table 22) than from the Charity I, Charity II, Lenawee, Colwood, and Hettinger soils o Nonexchangeable K released from the soils during the fourth cropping period was quite small, except, that K released from the Sims clay loam I. The relative high quantity of exchangeable K prior to and after the fourth crop is indicative of the K supplying capacity of this soil (Table 23)„ The correlation relating total yield to exchange­ able K (r = +0.74**) was significant, but it is difficult to provide a meaningful interpretation due to possible luxury consumption of K b y the first oat crop. 87 3. Labile Potassium in Soils Ionic equilibria play a fundamental role in fer­ tility relationships because they govern the ability of the soil to supply a particular nutrient. Of the essen­ tial cations in the soil, K is used in largest amounts by plants, whereas Ca and Mg are normally the dominant ca­ tions in arable soils. For a better understanding of the K status of soils, the activity of K/(Ca + Mg) 1 /2 equilibria in relation to adsorption characteristics of the soil mate­ rial are important. — - The capacity of a given soil to supply any partic­ ular nutrient is characterized by both the total amount of nutrient present and the energy level or intensity at which it is supplied. The relationship between these two para­ meters may be determined by the Quantity-Intensity (Q/I) method given by Beckett (1964a). This technique is based on thermodynamic principles, and holds promise of being applicable to all soils. Quantity-Intensity (Q/I) curves Appendix) illustrates how the A R (Figures 1-16, in the soil solution depends on the exchangeable K content of the soil repre­ sented by AK, which is the change in exchangeable K relative 88 to the value for exchangeable K at ARg , the equilibrium ratio, where the soil neither gains or loses K. Since nearly all the labile K in field soils is exchangeable (Figures 1-16, Appendix) gives a close approximation to the relationship between the amount of labile K (Quantity factor Q) and AR K (intensity factor I ) . The slope of the linear portion of the Q/I relation, AQ/AI, gives the amount of labile K that can be removed before A R e changes by a given a mount„ This represents the Potential Buffering K Capacity (PBC ) of the soil for K, as defined by Beckett (1964a) . 4, Equilibrium Activity Ratio and Potential Buffering Capacity of the Soils The part of the equilibrium curves (Figures 1-16, Appendix) , showing the relationship between release or a d ­ sorption of K by the soils and the activity ratio, were linear and allowed for estimates of A R fi and -AK values which are given in Table 24. Soils varied from 0.0009 to 0.0146 (moles/liter)^^ in their A R 0 values and are similar to those reported by Beckett (1964b) and Zandstra and MacKinzie (1968). All the TABLE 24.— Summary of soil potassium properties derived from equilibrium experi­ ments before and after cropping Soil Type Sample Relative to Cropping PK - l/2p (ca + Mg) ARg (M/1)1/2 Exchange­ able K (-AK) Meq/100 g. pb ck (-a k /a r | 1. Charity clay loam I before after 2.77 3.44 0.0024 0.0007 0.280 0.084 117.0 120.0 2. Charity clay loam II • before after 2.52 3.30 0.0050 0.0007 0.256 0.037 51.2 52.9 3. Lenawee clay loam before after 3.19 3.66 0.0009 0.0004 0.049 0.022 54.5 55.0 4. Sims clay loam I before after 2.46 2.85 0.0092 0.0025 0.294 0.175 31.9 70.1 5. Sims clay loam II before after 3.02 3.81 0.0015 0.0004 0.091 0.028 66.5 70.0 6. Sims clay loam III before after 3.14 3.82 0.0012 0.0005 0.098 0.042 81.6 84.0 7. Colwood loam before after 2.88 3.68 0.0015 0.0003 0.189 0.038 12.6 12.7 e. Conover loam before after 2.86 3.59 0.0020 0.0006 0.112 0.038 56.0 63.4 9. Miami loam before after 2.95 3.67 0.0016 Q.M08* 0.100 0.050 62.5 62.5 10. Hettinger silty clay loam before after 2.93 3.44 0.0013 0.0005 0.168 0.070 129.0 140.0 11. Brimby silt loam before after 3.23 3.68 0.0011 0.0003 Q.040 0.014 38.2 46.7 12. Breckenridge sandy loam before after 3.12 3.57 0.0015 0.0006 0.070 0.035 46.0 58.4 13. Hillsdale sandy loam before after 2.98 3.69 0.0033 0.0016 0.062 0.038 18.8 23.8 14. Hodunk sandy loam before after 2.62 3.60 0.0065 0.0014 0.161 0.035 24.8 25.0 15. McBride sandy loam before after 2.68 3.81 0.0122 0.0024 0.133 0.028 10.9 11.7 16. Metamora sandy loam before after 2.50 3.58 0.0146 0.0024 0.128 0.028 8.8 11.7 90 ARe values decreased with cropping, and the amount of the decrease tended to become greater with higher degrees of K saturation in the uncropped samples (Table 24). All -AK (meq/100 g. soil) values also decreased with cropping, but the amount of decrease was generally less for those soils having a low initial ARe value (Table 24). Higher PBC K tended to be associated with higher amounts of clay, which represented a major source of K released from nonexchangeable form during the cropping period (Table 24). The amounts of exchangeable K showed a poor correlation to PBC (r = -0.34). Exchangeable K determinations therefore did not provide information about the amount of K released from a soil per unit reduction in the AR K value. This can be explained on the basis that the kinetics of K release of nonexchangeable form from soil minerals during the cropping period was in no way measured. These data suggest that the immediate Q/I rela­ tion will regulate the uptake of K over a short period, but would not be expected to show a simple relation to the K status of the soil where the oats benefited from ini­ tially non-labile K released during the cropping period. 91 The -AK values, AR =0, indicative of release of K when were found to be correlated with exchangeable K prior to cropping when the exchangeable K was obtained by extration with 1 N NH.OAc. — 4 The correlation coefficients relating -AK to total K-uptake (r = +0.83***) and to ex­ changeable K (r = +0.84***) were in good agreement; also the correlation coefficients relating -AK with K-uptake of each crop, and with uptake of nonexchangeable K (r = +0.70**) were significant (Table 2 5). K The A R 0 values for Ke = 0, which were derived from the curves by interpolation, were correlated with corre­ sponding values obtained from equilibration of a single sample and expressed in logarithmic form. When confined to the samples before cropping the correlation coefficient (r = -0.77**) was significant. A significant correlation was obtained (r = +0.62**), relating the AR values to that portion of K-uptake derived from exchangeable K, that is, the reduction in exchangeable K during cropping, but K correlations relating A R e and yields for each crop, total yields, K-uptake by each crop, and total K-uptake were poor. K The A R e did not provide a measure of the amount of K available to the oat plants. 92 TABLE 2 5=— Correlation between -AK prior to cropping; potassium uptake, and yields of oats grown in green­ house on 16 Michigan soils Measurement Total K-uptake by oats K-uptake by crop 1 K-uptake by crop 2 K-uptake by crop 3 K-uptake by crop 4 Total yield of oats Exchangeable K prior to cropping Nonexchangeable K-uptake b y oats DF r 14 14 14 14 14 14 14 14 0.83*** 0.83*** 0.81*** 0.78*** 0.72** 0.59* 0.84*** 0.70** *Significant at 0.05 level. **Significant at 0.01 level. ***Significant at 0.001 level. This can be explained on the basis that K-uptake from soils represents uptake from a dynamic system that is not at equilibrium; therefore, rate processes involved with ion movement may become the limiting factor in deter­ mining absorption rates by plant roots. While the soil may have a more or less uniform distribution of ions, formity. initially the root alters this uni­ The influence of the plant root on the ionic conditions of the soil begins when the root starts to force its way through the soil. Since the diameter of the root is frequently larger than the diameter of the majority of soil pores, the root moves soil particles 93 aside and in so doing increases the density of soil in the immediate vicinity of the root so that it has greater than average density. This will also increase the concentration of exchangeable K per unit volume of soil. In addition to pushing the soil aside, the root will intercept K ions in its path and,absorbtion will occur. The root absorbs water and causes a flow of water through the soil toward the root. Since this water contains K ions, these ions are transported to the root. The amount reaching the root will probably depend on the water used and the K concen­ tration in the soil water. 5. Potassium Potential of Soils K The ARe indicates the status of the immediately exchangeable K and, therefore, should regulate exchange of K ions from the complex; the -AK denotes the amount of exchangeable K and supposedly rate at which the activity of K on the exchange complex decreases as K is removed from the complex as indicated by the PBC tivity ratio of K is reduced, . As the ac­ the diffusion gradient away from the complex is also reduced, and K supply to the plant root may be insufficient. Thus for plant nutrition 94 purposes, a correction in the -AK should be made which takes into account differences in buffering capacities between different soils (Zandstra and MacKenzie, By multiplying the -AK by the PBC measurements, 1968). the Q/I relation could be defined in a single parameter in which the -AK value of the soil is related to a standard PBC (Zandstra and MacKenzie, potential, 1968). This product, the K- is supposedly the amount of exchangeable K (-AK) multiplied by the ease of release of the K. A significant correlation coefficient (r = +0.56*) relating K-potential and K-uptake by the first oat crop was obtained; however, the correlation coefficients for the second (r = +0.40), third (r = +0.32), fourth (r = +0.30) crops, and total K-uptake (r = +0.42) were not significant. These results can be attributed to the decrease in the original labile pool of K by the first oat crop, such that when nonexchangeable K was released from the soils the PBC K (obtained prior to cropping) is no longer valid with respect to the amount of K released from the soil complex (labile K) per unit reduction in the AR . The correlation coefficients relating K potential to yields of each crop and to total yields were nonsignificant. 95 6 . The evaluation of exchangeable K. -AK. AR^, PBCK , and K-potential as indexes of plant available K Exchangeable K as determined by 1 N NH^OAc was more highly correlated with total K-uptake, total yields of four oat crops, and nonexchangeable K-uptake than -AK (Table 26). This may be explained on the basis that the NH 4 replaced most of the exchangeable K and possibly some fixed K along the "edge" sites of the clay minerals. An­ other possible explanation is that the extrapolation of the equilibrium curves should have included that K repre­ sented by the asymptotic convergence of the Q/I relation to the Q-axis. This method of extrapolation would have resulted in larger -AK values and improved the correlation coefficient relating -AK to total K-uptake. K The activity ratio (ARe ) is not a suitable index of plant available K and is in no way a measure of the rate of release of nonexchangeable K from the soil. The PBC K K as a single value (slope of -AK/ARe ) gave poor correlations as an index of K availability. was multiplied b y -AK» the product When PBCK (K-potential) was corre­ lated (r = + 0.56*) with the K-uptake of the first oat crop (Table 26). The data presented in Table 26 clearly shows K K TABLE 26.— Correlation coefficients relating exchangeable K, -AK, ARe , PBC , and K-potential with potassium uptake and yields of four oat crops grown in greenhouse on 16 Michigan soils Measurement Exchangeable^- K -AK total K-uptake b y oats K-uptake by crop 1 K-uptake b y crop 2 K-uptake b y crop 3 K-uptake b y crop 4 total yield of four oat crops yield of crop 1 yield of crop 2 yield of crop 3 yield of crop 4 nonexchangeable K-uptake 0.98*** 0.91*** 0.97*** 0.92*** 0.94*** 0.74** 0.16 0.74** 0 .6 6 ** 0.78*** 0.82*** 0.83*** 0.83*** 0.81*** 0.78*** 0.72** 0.59* ^Extracted with 1 N NH^OAc for 10 minutes. — 4 ♦Significant at 0.05 level. **Significant at 0.01 level. ***Significant at 0.001 level. 0.10 0.57* 0 .6 6 ** 0.70** 0.70** PBC k K-potential 0.29 0.30 0.35 0.09 0.24 0.15 0.21 0.11 0.06 0.29 0.42 0.56* 0.40 0.32 0.30 0.41 0.10 0.11 0.16 0.32 0.29 0.23 0.32 0.45 0.46 0.43 0.17 -0.08 -0.08 -0 . 1 0 -0 . 1 2 -0.13 -0.06 97 that exchangeable K (1 N NH^OAc extractable) was a better index of total supply of K than equilibrium exchangeable K (-AK) under exhaustive cropping; but this does not neces­ sarily mean that exchangeable K extracted with NH^OAc would be a superior index under field conditions, because K re­ serves would seldom be as severely depleted as they were in the greenhouse pot trial. The soils used in this study released large amounts of K from nonexchangeable form and, therefore, provided an extremely complicated medium when trying to assess the K supplying p o w e r . SUMMARY AND CONCLUSIONS EFFECTS OF RATES AND SOURCES OF POTASSIUM ON YIELDS, SPECIFIC GRAVITY, MINERAL CONTENT AND REDUCING SUGAR CONTENT OF BURBANK AND SEBAGO POTATOES The objectives of the field investigation were to compare the effects of various rates and sources of K on s (1 ) yields and specific gravity of tubers, (2 ) the uptake and distribution of K, Ca, and Mg in potato tissue, and (3) reducing sugar content of potato tubers at harvest. The results from this field investigation are summarized as follows: 1. Significant yields of potatoes for the 1967 grow­ ing season were obtained from application rates of K2Q as KCl up to 180 pounds per acre with a 210 pound per acre level of exchangeable K. 2. A significant yield response was obtained from 150 pounds of applied K_0, but was independent of K source when the level of exchangeable K was 270 pounds per acre. 99 100 3. Specific gravity decreased significantly with in­ creasing applications of KCl on both Burbank and Sebago varieties, but larger decreases were found for the Sebago variety. For the source of K study/ KNO^ decreased the specific gravity on the Sebago variety at the (0.05 level) when compared to KCl, K 2 S 0 4# and K 2 C 0 4. 3 sources. Potassium concentrations in potato petioles, leaves, whole plants and tubers increased with increased applications of K 2 0 ; however, for all tissue sampled there was a decrease in K as maturation of the plant occurred. The magnitude of K concentrations were petioles > leaves > whole plants > tubers. Potas­ sium concentration in potato plant tissue averaged over three sampling dates shows that the greatest range of K concentrations are found to be petioles > whole plants > leaves > t u b e r s . 5. For the source of K study the concentrations of K in petioles and leaves were high at the early season sampling and decreased in magnitude with increasing maturation of the plant. When all sampling dates 101 were averaged KC1 as a source of K resulted in higher concentrations of K in the petioles level) when compared to l^SO^. The (0.01 source resulted in higher concentrations of K in the petioles (0 . 0 1 level) when compared with and KN 0 3 . 6 . Concentrations of Ca in petioles, leaves, and whole plants decreased with increasing rates of applied K, but increased with maturation of the plant. These results suggest once the suppression of Ca uptake occurs it remains suppressed through­ out the growing season and the magnitude of sup­ pression will increase as the rate of applied K increases. petioles, Concentrations of Ca found in the leaves, and whole plants were sixty to eighty times that found in tubers. Sources of K resulted in suppression of Ca uptake when compared with the no K treatment. However, there were no significant differences between sources of K and suppression of Ca uptake probably eliminating any external anion effect. 102 7. Magnesium concentrations in petioles, leaves, and whole plants generally decreased with increasing rates of K and increased as the plants matured. Applications of 240 and 480 pounds of 1^0 per acre decreased the concentration of Mg in the petioles, leaves (Table 8 ), and whole plants (Table 9) resulting in a K induced decrease in Mg much larger in magnitude than a K induced decrease in Ca. This may be a partial explanation for the decrease in yields obtained from the higher rates of applied K^O (Table 1). Concentrations of Mg were 8-12 times higher in magnitude in pet-ioles, leaves, and whole plants than in tubers. Potassium carbonate as a source of K decreased Mg content in petioles to the K 2 S0^ source. treatment, ^ C O ^ . When compared to the no K decreased the Mg concentration significantly at the 8 (0.05 level) when compared 0.01 level. Rates and sources of K had no significant effect on the reducing sugar content of tubers at harvest for the Burbank or Sebago varieties. EVALUATION OF POTASSIUM QUANTITY-INTENSITY RELATIONSHIPS OF SELECTED MICHIGAN SOILS The equilibrium activity ratio (AR ) and equilibrium exchangeable K (-AK) were obtained from curves of . . a a, »1/2 K activity ratios, K/ (Ca + Mg) or AR , against changes in exchangeable K (AKe) based on equilibration of the soils in 0.00159 M C a C ^ K. containing different amounts of These were compared to exchangeable (1 N NH^OAc ex- tractable) K measurements and related to total K-uptake and yield responses of four oat crops grown in the green­ house without added K. The findings may be summarized as follows: 1. Exchangeable K ( I N NH^OAc extractable) was corre­ lated with yields K-uptake (r = +0.75**), nonexchangeable (r = +0.98***) b y four oat crops. Non­ exchangeable K-uptake amounted to 50 percent or more of total K-uptake by oats grown on all soils, except Hodunk, McBride, and M e t a m o r a . 103 104 2. Equilibration of soils in 0.00159 M C a C ^ ing 0, 0.230, 0.716, contain­ 1.43, and 1.81 mmoles of KC1 resulted in activity ratios (AR ) which gave a higher correlation (r = +0.63**) with that part of K-uptake derived from the exchangeable form than with the total K-up t a k e . 3. Estimates of the quantities of K released (-AK) as obtained from equilibrium curves were found to be much more indicative of the total K-uptake (r = +0.83***) and to exchangeable K (r = +0.84***) prior to cropping than were the AR^ values. i-AK The values were correlated (r = +0.70**) with K- uptake of the nonexchangeable form. 4. The PBC K K as a single value (slope of -AK/AR ) gave poor correlations as an index of K availability. PBC When was multiplied b y -AK# the product (K-potential) was correlated (r = +0.56*) with the K-uptake of the first oat crop. This supports the principle that the Q/I relationship derived from the equilib­ rium curves is for the immediate labile pool of K, and in no way measures the kinetics of K re­ lease from nonexchangeable form. LITERATURE CITED Adams # and Henderson# J. B. 1962. Magnesium avail­ ability as affected by deficient and adequate levels of potassium and lime. Soil Sci. Soc. Amer. Proc. 26s65-68. Arnold# P. W. 1960. Nature and mode of weathering of soil-potassium reserves. J. Sci. Food Agr. 6 s 285-292. Arnold# P. W. 1962. The potassium status of some Eng­ lish soils considered as a problem of energy re­ lationships. Proc. Fertilizer Soc. No. 72# 25-43. Beckett P. H. T. 1964a. Studies on soil potassium. I. Conformation of the ratio laws Measurement of potassium potential. J. Soil Sci. 15s1-8. Beckett P. H. T. 1964b. Studies on soil potassium. I. The "immediate" Q/l relations of labile po­ tassium in the soil. J. Soil Sci. 15s9-23. Beckett P. H. T. and Nafady# M. H. M. 1964. 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Experiments on the decomposition of silicates and discussion of chemical weather­ ing. Clays and clay minerals 10:443-459. Pergamon Press, New York. Cummings# G. A. and Houghland# G. V. C. 1939. Fertil­ izer placement for potatoes. U.S.D.A.# Tech. Bull. 669. Denison# I. A.# Fry# W. H . # and Gile# P. L. 1929. Al­ terations of muscovite and biotite in the soil. U.S.D.A. Tech. Bull. 128# p. 32. Doll# E. C., Christenson# D. R. 1966. Routine soil test determination of magnesium using an atomic ab­ sorption spectrophotometer. Quart. Bull. Mich. -Agr. Exp. Sta.# East Lansing# Mich. 49:216-220. Doll, E. C. and Hossner# L. R. 1964. Magnesium defi­ ciency as related to liming and potassium levels in acid sandy podzols. 8 th Intern. Congress of Soil Science# Bucharest# Romania. 4:907-912. Dunn# L. E.# Rost# C. O. 1948. Effect of fertilizers on the composition of potatoes in the Red River Valley of Minnesota. Soil Sci. Soc. Amer. Proc. 13:374-379. 107 Dunn, L. E. and Nyland, R. E. 1945. The influence of fertilizers on the specific gravity of potatoes grown in Minnesota. Amer. Potato J. 22:275-288. Ellis, B. G. and Mortland, M. M. 1956. Rate of potassium release from fixed and native forms. Soil Sci. Soc. Amer. Proc. 23:451-453. Hawkins, A. J., Chucka, J. A., and MacKinzie, A. J. 1947. Fertility status of potato soils of Aroostook County, Maine, and relation to fertilizer and ro­ tation practices. Maine Agr. Exp. Sta. Bull. 454. Hawkins, A. 1965. New ways of fertilizing potatoes. Amer. Potato J. 42:76-77. Herman, T . , and Merkle, F. G. 1963. The influence of chlorides on yield and specific gravity of pota­ toes. Amer. Potato J. 40:1-7. Hossner, L. R . , Doll, E. C.» and Thurlow, D. L. 1968. Effect of magnesium fertilization on yield and magnesium uptake b y potatoes. (Manuscript in preparation.) Houghland, G. V. C. and Shricker, F. A. 1933. The ef­ fects of potash on starch in potatoes. Jour. Amer. Soc. Agron. 25:334-340. Hovland, D. and Caldwell, A. C. 1960. 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Lucas# R. E. and Scarseth# G. D. 1947. Potassium# cal­ cium and magnesium balance and reciprocal rela­ tionship in plants. Jour. Amer. Soc. Agron. 39:887-896. Lucas# R. E.# Wheeler# E. J . # and Davis# J. F. 1954. Effect of potassium carriers and phosphate-potash ratios on the yield and quality of potatoes grown in organic soils. Amer. Potato J. 31:349-352. Marshall, C. E. 1964. The Physical Chemistry and Min­ eralogy of Soils I. John Wiley and Sons# Inc.# New York# New York. Mathews, B. C. and Beckett# P. H. T. 1962. A new proce­ dure for studying the release and fixation of po­ tassium ions in soil. J. Agri. Sci. 58:59-64. Mortland, M. M. 1958. Kinetics of potassium release from biotite. Soil Sci. Soc. Amer. Proc. 22:503-508. Mortland# M. M. 1961. The dynamic character of potassium release and fixation. Soil Sci. 91:11-13. Mortland# M. M. and Ellis# B. G. 1959. Release of fixed potassium as a diffusion controlled process. Soil Sci. Soc. Amer. Proc. 23:363-364. 109 Mortland# M„ M. # Lawton# K . # Vehara# G. 1956. Alteration of biotite to vermiculite by plant growth. Soil Sci. 82:477-481. Mulder# E. G. 1956. Effect of the mineral nutrition of potato plants on the biochemistry and the physi­ ology of the tubers. Neth. J. Agr. Sci. 4-5:333356. Murphy# H. J . # Goven# M. potash on yield# russeting of the Amer. Potato J. J. 1965. Influence of source of specific gravity# and surface Russet Burbank variety in Maine. 42:192-194. Murphy# H. J . » Goven# M. J. 1966. The last decade in 38 years of potash studies for potato fertilizers in Maine. Amer. Potato J. 43:122-127. Nelson# N. 1944. A photometric adaptation of the Somogyi method for the determination of glucose. J. Biol. Chem. 153:375-380. Nelson# W. L. and Hawkins# A. 1947. Response to Irish potatoes to phosphorus and potassium on soils hav­ ing different levels of these nutrients in Maine and North Carolina. Jour. Amer. Soc. Agron. 39: 1053-1063. Reitemeier# R. F.# Brown# I. 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APPENDIX 114 CHARITY CLAY LOAM I .9 0 .6 0 .4 5 CROPPING O BEFORE A AFTER .3 0 + .1 5 a Ke meq/ lOOg soil .7 5 0 15 ;//. o n & / .0 0 5 . . s n.01 ar .015 M m .02 1025 / d 1^ .3 0 Fig. 1.— Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Charity clay loam I. 115 CHARITY CLAY LOAM n 1.05 A Ke meq/IOOg soil .9 0 .7 5 .6 0 CROPPING O BEFORE A AFTER .4 5 5 0 5 >005 > .01 .015 .02 .025 .03 ARK ( M / l) '/2 .3 0 Fig. 2.— Relation of potassium activity ratio (ARK ) to -AK before and after cropping on Charity clay loam II. 116 LENAWEE CLAY LOAM Ke meq/IOOg soil I .0 5 CROPPING O BEFORE A AFTER < + . 15 .0 0 5 .01 .015 .02 .025 A R k (M/I),/* Pig. 3.— Relation of potassium activity ratio (Ar {b ) to -AK before and after cropping on Lenawee clay loam. 117 Ke meq/IOOg soil SIMS CLAY LOAM I CROPPING BEFORE AFTER a j___ i .015 .02 .025 .03 A R k ( M / I ) *'2 Fig. 4.— Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Sims clay loam I . 118 SIMS CLAY LOAM H 1.05 Ke meq/IOOg soil .9 0 .7 5 .60 .4 5 CROPPING O BEFORE A AFTER .3 0 <3 X>X)o4 - .01 .015 .02 .025 .005 Fig. 5.— Relation of potassium activity ratio (AR^) to -AK before and after cropping on Sims clay loam II. SIMS CLAY LOAM I E Ke meq/ lOOg soil .9 0 .6 0 .4 5 .3 0 - CROPPING O BEFORE A AFTER + Fig. 6.— Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Sims clay loam III. 120 COLWOOD LOAM 1.20 1.05 .7 5 .6 0 45 CROPPING O BEFORE A AFTER .3 0 a Ke meq/IOOg soil .9 0 .015 .02 Fig. 7.— Relation of potassium a c ­ tivity ratio (ARe) to -AK before and after cropping on Colwood loam. CONOVER LOAM .9 0 Ke meq/IOOg soil .7 5 .6 0 .4 5 CROPPING O BEFORE A AFTER .3 0 + AO Fig. 8 .--Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Conover loam. 122 MIAMI LOAM .9 0 Ke meq/IOOg soil .7 5 .6 0 CROPPING .4 5 O BEFORE A AFTER .3 0 + .15 0 -.15 .01 .015 .02 .025 .03 A R K ( M / l ) ,/2 Fig. 9.— Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Miami loam. 123 soil HETTINGER SILTY CLAY LOAM Ke meq/IOOg CROPPING O BEFORE A AFTER to .0 0 5 T)1 iOI5 !02 .0 2 5 A R k {M/I)'/2 Fig. 10.— Relation of potassium activity ratio (AR^) to -AK before and after cropping on Hettinger silty clay loam. BRIMLEY SILT LOAM CROPPING O BEFORE A AFTER .7 5 A-— .6 0 © (A O ” .4 5 o» • O' 0> o ro O O + .1 5 E 0> < 0 - . 15 ■ .005 i .01 i ■ .015 ■---------- 1-----------1 .02 i .025 i---------- 1 .03 AR k ( M / I ) 1/2 .3 0 Fig. 11.— Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Brimley silt loam. 125 BRECKENRIDGE SANDY LOAM 90r a Ke meq /lOOg soil .7 5 .6 0 .4 5 CROPPING O BEFORE A AFTER .3 0 +.15 0 -.15 A O i » .005 » » .01 « ■ .015 » ■ ■ .02 ■ .025 «___ i .03 A R K (M7Ul(2 .3 0 Fig. 12.— Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Breckenridge sandy loam. HILLSDALE SANDY LOAM CROPPING O BEFORE A AFTER a Ke meq/IOOg soil .60 .45 - .30 + 1--- 1--- I--- L— .005 .01 .015 Fig. 13.— Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Hillsdale sandy loam. 127 HODUNK SANDY LOAM ,90r .7 5 CROPPING OBEFORE A AFTER Ke meq/IOOg soil .6 0 .4 5 .3 0 .015 .02 .0 2 5 .03 .035 A R k (M/I)I/8 .3 0 Fig. 14.— Relation of potassium activity ratio (ARe ) to -AK before and after cropping on Hodunk sandy loam. 128 A Ke meg / lOOg soil Me BRIDE SANDY LOAM CROPPING O BEFORE A AFTER .015 .02 .025 .0 3 .035 .04 X)45 AR* ( M / I ) K Fig. 15.— Relation of potassium activity ratio (AR^) to '*-AK before and after cropping on McBride sandy loam. METAMORA SANDY LOAM a Ke meq /lOOg soil CROPPING O BEFORE A AFTER .30 r + .30 Fig. 16.— Relation of potassium activity ratio (AR^) to -AK before and after cropping on Metamora sandy loam.