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The application of Mitscherlich's growth law and pot method of soil testing to nutritional studies with.. Dickson, Bruce Anderson 1942-12-31

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L £h i5i ft* THE APPLICATION 0? MITSCHERLICH»S GROWTH LAW AND POT METHOD OF SOIL TESTING TO NUTRITIONAL STUDIES WITH RASPBERRIES AND OATS by Bruce Anderson Dickson A T h e s i s submitted i n P a r t i a l F u l f i l m e n t o f The Requirements f o r the Degree of MASTER OE SCIENCE IN AGRICULTURE i n the Department of HORTICULTURE The U n i v e r s i t y of A p r i l , B r i t i s h 1?42 Columbia Table of Contents Acknowledgments 2 Introduction . . . . . . . . . . . . . 3 Review of the Mitscherlich growth law' 4 Part I An Experiment with Cuthbert Raspberries Introduction . . . . . . . . . . . . . . . . . . . 12 Experimental Materials and control of conditions 13 Plan of experiment 14 Harvest methods 16 Methods of analysis 16 Results of the raspberry experiment The dry weight data . . . 17 The maximum possible y i e l d . . . . 18 The proportionality constant . . . . . . . . 19 The f e r t i l i t y of the sand-peat mixture. . . . 20 Calculation of the yields for a true logarithmic curve . . . . . . . . . 21 Results of raspberry analysis . 24 Conclusions on the raspberry experiment 27 Part I I An Experiment with Oats Introduction 30 Experimental . . . 31 Apparatus, s o i l samples, mixing procedure, plant material, watering control of conditions.31 Feeding plan and stoek solutions 33 Harvest methods . . . . . . . . . 35 Methods of analysis 36 Results of the oat experiment Dry weight data 36 The maximum possible y i e l d . 40 The proportionality constant 41 S o i l nitrogen . . . . . . . . . . . . . . . . 42 Calculations of the yields for a true logarithmic curve . 42 Results of chemical s o i l tests . . . . . . . . . . 45 Results of plant analysis . . . . . . . . . . . . 47 Conclusions on the oat experiment . . 52 General conclusions on the application of the Mitscherlich method to raspberries and oats . . . . . . 57 Bibliography . 61 (2) Acknowledgements The writer takes great pleasure i n acknowledging the assistance of Dr. G.H.Harris, Associate Professor of the Department of Horticulture, University of B r i t i s h Columbia, i n the administration of the experi mental work of the raspberry experiment, the chemical analysis, and the preparation of the manuscript. Acknowledgements are also extended to Mr. J,J.Woods* Superintendent of the Dominion Experiment Station, Saanichton, B.C., who generously provided the equip- ment, materials, and time for the oat experiment, and he l p f u l l y c r i t i c i z e d the manuscript. Thanks are tend ered to Mr. T.H.Anstey, graduate i n plant n u t r i t i o n , for proof-reading the manuscript, and to Miss Kathleen Woods for her very excellent typing. THE APPLICATION OP MITSCHERLICH»S GROWTH LAW AND POT METHOD OP SOIL TESTING TO NUTRITIONAL STUDIES WITH RASPBERRIES AND OATS Introduction The importance of determining the manurial requirements of s o i l s and the interpretation of these determinations i n terms of probable plant y i e l d s , has long been recognized by ag r i c u l t u r i s t s . A method which purports to form a new app roach to this problem and which has enjoyed considerable popularity i n Europe for the past t h i r t y years, has been pro posed by E. A. Mitscherlich (8) of Konigsberg, Germany. Although Mitscherlich published his f i r s t papers on his plant method of s o i l testing i n 1909, they recieved l i t t l e atten tion i n the English language publications u n t i l 1932 when Stewart, of the Imperial Bureau of S o i l Science, published a li t e r a t u r e review of the subject (13). Since then, however, Capo (4), Hartung (5), Macy (6), Magistad (7), and Willcox 9 (15), a l l of North America, have made contributions on the Mitscherlich method. The Mitscherlich method for s o i l f e r t i l i t y investiga tions i s essentially the study of the trend of the yields from a series of plants grown to maturity under a systematic scheme of f e r t i l i z a t i o n . Mitscherlich i s so convinced of the v a l i d i t y of his method that he claims, and offers proof(9), that he has derived a general y i e l d law which i s amenable to mathematical treatment. He also claims that when specially designed experiments are considered i n the l i g h t of his y i e l d law, a quantitative relationship between s o i l f e r t i l i t y and plant y i e l d may be found. Recognizing the impotence of these claims, i t was de cided to test the v a l i d i t y of the Mitscherlich method and to ascertain, thereby, whether an application of i t would be of value i n supplimenting the rapid chemical methods (10). (12) of estimating s o i l f e r t i l i t y now i n popular use i n B r i t i s h Columbia. I t was decided also to investigate whether the use of the Mitscherlich method with different a g r i c u l t u r a l plant types would suggest an improved technique for plant n u t r i t i o n experiments. With this purpose i n view, two experiments were under taken. The f i r s t , during the summer of 1940, was an exper iment i n the nitrogen n u t r i t i o n of Cuthbert raspberries, and the second, during the season of 1941-1942, was an experiment with oats, where the method was used i n conjunction with the rapid chemical s o i l test methods. Review of the Mitscherlich Growth Law Many of the early workers i n the f i e l d of plant n u t r i  tion such as Leibig, H e l l r e i g a l , and Wagner, began experimen tation by studying the effect of varying the application of a single nutrient from an ample l e v e l down to a zero applic ation, at the same time keeping a l l other known growth factors at an ample l e v e l . Although some of these men ob-tained excellent results (9), the f u l l mathematical possib i l i t i e s of their y i e l d curves were not pointed out u n t i l Mitscherlich recognized the s i m i l a r i t y i n the shape of these growth curves and postulated that i f the experiments were done under specified conditions, a general equation could be written which would apply to a l l of them. Mitscherlich studied these growth curves, as well as those obtained from his own experiments, and concluded that the y i e l d was a logarithmic function of a growth factor, when that factor was increased i n unit Increments from zero, a l l other growth factors being*supplied at an ample l e v e l ( 9 ) . Expressed In symbols, his r e l a t i o n i s represented by, which states b r i e f l y that the Increment of y i e l d , dy, obtain ed per unit increment of growth factor, dx, i s proportional to the decrement from the maximum ( i . e . proportional to the difference between the y i e l d obtained, y, and the maximum possible y i e l d of the series, A). In order to equate these quantities, the right hand side i s multiplied by the needed numeral, which may be known as a proportionality constant, or effect factor, c. (I) When integrated and transformed this equation becomes log(A-y) = logA - c.x - ( I D or, solving for y: y = A ( l - 1CT C X) - - - - - ( H I ) This i s a general equation which has already been f i t t e d to many natural phenomena. Stewart (13) points put that this logarithmic equation i s i d e n t i c a l with the equation applied to the velocity of reaction of a monomolecular chemical change at constant temperature, such as the decomposition.of hydrogen peroxide i n aqueous solution. I t i s also i d e n t i c a l with that applied to the rate of radio-active disintegration of metals. Under some circumstances, i t has been found d i f f i c u l t to determine the maximum possible y i e l d , A, of the series experimentally. I t can, however, be calculated by simultan eously solving three equations. In order to do t h i s , the increments of growth factor must be deliberately chosen so that xg-X3 = x^-Xg. The resulting yields may then be applied to the three equations of the form(II), which may take the rearranged form of a (To)2 - (y-.) (yQ . (iv) & ~ 2(y2) - (yl) - (y 3) where y^, yg, and y 3 are the yields obtained from f e r t i l i z e r treatments x-^ , Xg, and x^ respectively. Thus, having obtained the experimental y i e l d data, the most probable value for the maximum y i e l d may be calculated and used i n subsequent calculations. In the foregoing equations, the symbol x represents the amount of the growth factor added to the s o i l . One treat ment i n the series, however, recieves none of the growth factor i n question, so that I f a y i e l d i s obtained at a l l i n that treatment, i t i s the result of the amount of the growth factor o r i g i n a l l y present i n the s o i l . The amount of growth factor i s designated by the symbol b. As a result of i t s presence i n a l l of the pots the whole growth curve i s di s  placed upwards by a given amount. Therefore, i n order to complete the meaning of equation ( I I ) , the t o t a l amount of the growth factor present i n the s o i l i s represented by, x + b. The equation now becomes log(A-y) = logA - c(x+b) (y) Since both b and c are, as yet, unknown quantities i n this equation, two such equations must be solved simultaneously, the condensed form of which i s log(A-y-j) - log(A-yg) c = £ — (VI) x 2 - x x The solution of equation (VI) provides us with a number called a proportionality constant, c, which makes i t possible to interpret Mitscherlich's y i e l d law as a workable equation. Mitscherlich goes further than t h i s , however, and shows that this number i s characteristic of the slope of the y i e l d curve and that this number i s always the same for a given growth factor, regardless of the plant used, provided he -8- uses the same size of pot, the same weight of s o i l , and the same units of measurement i n a l l of the experiments. He, therefore, gives this proportionality constant special s i g  nificance by c a l l i n g i t an "effect factor of the growth factor" (9). When the proportionality constant, c, i s found by solv ing equation (VI), then equation (V) may be solved for b, the amount of growth factor o r i g i n a l l y present i n the s o i l . When rearranged equation (V) becomes logA - log(A-y Q) b = _ _ _ _ _ _ _ _ _ . (VII) c where y 0 i s the y i e l d obtained when the s o i l received a l l of the growth factors except the one concerned i n the series. Having, obtained a l l of the Information required for equation (V), the calculation procedure may be reversed and the y i e l d s , y, which theoretically should have been obtained in the experiment, may be calculated. This i s done purely as a check on the y i e l d law, that i s , to see how closely the y i e l d curve obtained resembles a true logarithmic curve of the same slope (same proportionality constant,).- Conducting n u t r i t i o n experiments i n this quantitative manner not only affords us a means of evaluating s o i l f e r t  i l i t y i n terms of actual weight of growth factors, but i t also affords us a means of evaluating i t i n terms of plant y i e l d . Thus, when the y i e l d i s plotted as percent of the maximum, the amount of growth factor required for a 50% y i e l d can quickly he determined. Mitscherlich's law states that the increase i n growth per unit of factor i s propor t i o n a l to the decrement from the maximum. Prom thiSj i t follows that i f the amount of f e r t i l i z e r required for a 50% y i e l d i s doubled, i t w i l l give an increase of 50% of the decrement, that i s , 50$ of 50% = 25%, and the y i e l d from the doubled amount w i l l be 75% of the maximum. Baule(2) has proposed that the amount of each nutrient required for a 50% y i e l d be designated as a "food u n i t " (now known as the Baule u n i t ) . Furthermore, i t has been found that when half the maximum y i e l d i s obtained i n one of such a series, the amount of growth factor present i s one tenth as high as i t i s for the maximum. Thus, although four Baule units w i l l t h eoretically produce a 93.75$ yield', i t w i l l take more than twice as much (10 Baule units) to raise i t to 100%t provid ing toxic conditions are not reached for the plant species being used. Mitscherlich's y i e l d law and Baule's proposal for "food u n i t " evaluation of nutrients are diagramatically represented i n Figure 1. In experiments which I l l u s t r a t e this growth law, i t has been generally found (15) that, i n sand or s o i l s of low phos phate f i x i n g power, the maximum y i e l d i s obtained when the Figure 1. Diagramatie Representation of Mitscherlich's Y i e l d Law and Baule's "food units" of Growth Factor. -11- three main factors are present In the r a t i o 5:lj2 (U:P2G5:K2O) Thus when the phosphate and the potash are at their maximum values for growth and nitrogen i s varied upwards In unit Increments from zero, the greatest y i e l d i s obtained where the nitrogen i s 5 times higher than the phosphate and 2\ times higher than the potash. The same re l a t i o n has been found when the other growth factors are varied i n turn. The details of the Mitscherlich technique for I l l u s t r a t  ing this law are given i n his own book (8). 'The most d e t a i l  ed English language account of the procedure Is that gjven by Stewart (13). v -12- Part I AN EXPERIMENT WITH CUTHBBRT RASPBERRIES Introduction For several years now one of the major problems of the Eraser Valley of B r i t i s h Columbia has been that concerned with the d i f f i c u l t i e s met i n raspberry growing. Many d i f f  erent phases of the problem have been studied by the personnel of the B r i t i s h Columbia Raspberry Committee (14). The importance of nitrogen f e r t i l i z e r s i s generally recognized by this body. According to Woods (14), results from both the Experimental Farm at Agassiz and the plots at Hatzic, show that only nitrogenous f e r t i l i z e r s are of value, although he could f i n d no consistant correlation between the analysis of s o i l s from "good" and "poor" plantations. Harris (14) has stressed water as being of prime importance and has shown good results with nitrogen and phosphates as n u t r i t i o n a l factors i n the raspberry problem. The nitrogen n u t r i t i o n of the raspberry plant, therefore, has been and s t i l l i s an important part of the raspberry decline problem, and the author f e l t that the quantitative methods originated by Mitscherlich should be t r i e d as a new approach. Chemical analysis of the plant material was carried out for the purpose of finding out whether or not the percentage composition and the t o t a l nutrient content were i n any way -13- correlated with the s o i l nutrient l e v e l and the obtained y i e l d . • i Experimental Materials and Control of Conditions Twenty-five ten Inch clay pots were thoroughly washed and dried. The in t e r i o r s of these pots were then heated by inverting over an e l e c t r i c hotplate and thoroughly coated (inside only) with melted paraffin (Parawax). The pots were f i l l e d with a mixture of washed sand and freshly powdered peat of low f e r t i l i t y value. This mixture was 50-50 by volume (approximately 6100 grams dry sand and 400 grams dried peat per pot). From the apparent specific gravity of this mixture, the acre weight to a depth of s i x inches was deter mined as 3,764,000 pounds. Twenty-five Cuthbert raspberry suckers were selected on the basis of uniformity of size from 300 or more taken from the University f i e l d p l o t s . Variations i n vigor and growth power were present never-the-less and ultimately caused considerable error i n the experiment. The roots of the plants were washed free of s o i l and they were then transplanted to the pots on May 18, 1940. The nutrient solutions were administered and the experiment was continued during the summer months u n t i l October 11, 1940. The experiment was set up i n a lath-house south of the -14- Uhiversity greenhouse, p a r t i a l shade being given by four- inch planks spaced four inches apart, s i x feet above the surface of the pots. At times of heavy r a i n f a l l a canvas was spread over the top of the lath-house to prevent the flooding of the pots and the consequent overflowing of the drainage pans. Disease and pest controls were made with lime sulphur and nicotine sprays. The raspberry saw-fly succeeded i n causing small in j u r i e s to the leaves before they were s a t i s  f a c t o r i l y controlled. Plan of Experiment The series of raspberries were supplied with ample amounts of a l l nutrients including water, except nitrogen, which was varied downward from an ample l e v e l to a d e f i n i t e l y deficient l e v e l . The ample l e v e l was derived from Baule's food unit eval uation of nutrients(15). For example, when 225 pounds of nitrogen are available to an acre of a crop, I t w i l l make a 50% y i e l d . Thus, 4 units or 900 pounds nitrogen per acre w i l l give a theoretical y i e l d of 94% In a f i e l d t r i a l . The efficiency of the f e r t i l i z e r , however, i s increased (on an area basis) when i t i s confined to a pot. Therefore, 2§ Baule units of nitrogen (550 pounds per acre) were used as an ample l e v e l . The same l e v e l was used for the potash but the phosphate application was derived on a 6 Baule unit basis In -15- order to take care of possible f i x a t i o n i n insoluble forms. In this experiment the nitrogen was the only variable, being supplied at s i x different lev e l s . (1) . 0.12 gm N per pot (2) 0.33 " (3) 0.54 " (4) 0.67 " (5) 1.34 » (6) 2.01 " These values were chosen such that (2)-(1) = (3)-(2) and (5)-(4) = (6)-(5|. i n order that the y i e l d values obtain ed would be applicable to equation (IV) which i s A — 2(y f) - ( y i) - (y 3) where A is. the calculated maximum possible y i e l d and y-j_, y 2, and y 3 are the yields obtained either from treatments (1), (2), and (3) or (4), (5), and (6), respectively, expressed i n grams dry weight. The Pg0 5 was supplied i n the same amount to a l l the pots, namely 1.03 gm per pot (1.71 gm monocalcium phosphate). The K 20 was supplied i n a similar manner at 0.815 gm per pot (1.62 gm potassium sulphate). The minor elements were supplied to each pot as follows^ -16- MgS04 400 mg M11SO4 100 mg CuS04 20 mg FeS04 50 mg H 3B0 3 4 mg • The experiment was kept well moistened throughout the growth period. The drainage water was returned carefully to i t s respective pot at each watering so that no nutrients were l o s t from the system. The experiment was done In quadruplicate. The single check pot received no f e r t i l i z e r at a l l . Harvest Methods The lower leaves which showed signs of dropping off during the experiment were harvested from time to time and were kept i n labeled bags. On October 11, the rest of the leaves were stripped off . The canes were cut up into small pieces. The roots were so th i c k l y matted that i t was found d i f f i c u l t to wash them completely free of sand. Most of i t shook free however, when the roots were dry. The material was dried to a constant weight at 75-80*0. Both top weights and root weights were obtained. Methods of Analysis The dried plant material from each pot (roots, stems, and leaves) was ground to a coarse meal In a meat grinder. The nitrogen analysis was run i n t r i p l i c a t e and two gram -17- samples were used In order to minimize the sampling error. The Kjeldahl method was used (1). Ash solutions were made on f i v e gram samples. The phosphate determinations were made on the ash solution using Tschopp's method as modified for use with the B.D.H. Nesslerizer color discs (3). The potash i n the ash solution was determined by the S h e r r i l l centrifuge method (11). Results of the Raspberry Experiment The Dry Weight Data The yields obtained i n the experiment are shown i n Table 1. The figures are the dry weight of the whole plant (roots, stems, and leaves). The general trend of increase i n y i e l d with Increase in nitrogen l e v e l was evident i n spite of the rather large de vi a t i o n and lack of conformity w i t h a true logarithmic curve _(Figure 2). Since the phosphate and potash were supplied at 1.03 and 0.815 gm per pot respectively, i t w i l l also be seen from the table that the y i e l d continued to In crease u n t i l the nitrogen was twice as high as the phosphate or potash. By far the most satisfactory growth was obtained in the high nitrogen treatment, where the canes were nearly s i x feet t a l l , 5/8 inches thick at the base and supported large healthy leaves. The low end of the series showed definite -18- nitrogen starvation symptoms of small yellow leaves and very spindly canes. I t w i l l also be noted from Table 1 that, although the check plant was d e f i n i t e l y smaller than that of the lowest nitrogen application, i t made su f f i c i e n t growth to indicate the presence of a small amount of nitrogen i n the sand-peat mixture. Table 1. Total Dry Weight of Raspberry Plants Resulting from Nitrogen Supplied at Different Levels Nitrogen Applic- . Dry Weight of Plants ations per pot (gm) Replications Average Check • — — — — — .__ 36.4 0.12 30.6 93.0 36.2 71.2 57.8 0.33 120.0 103.6 104.9 103.4 107.9 0.54 . 127.1 90.7 105.8 119.1 110.7 0.67 128.3 63.4 109.6 167.5 117.2 1.34 126.2 138.3 157.9 134.8 139.3 2.01 156.7 204.6 191.3 204.6 189.3 The Maximum Possible Y i e l d The marked varia t i o n i n this experiment, as shown i n Table 1, makes the use of calculations rather hazardous. However, since the general trend i s present, certain of the values obtained may be used as the basis of approximate -19- calculations. The yields which best suit the lo g a r i t h i c curve are 71.2 gm, 103.4.gm, and 127.1.gm. These yields were obtained from pots supplied with nitrogen at 0.12 gm, 0.33 gm, and 0.54 gm respectively. Applying this informa tion to the equation? (103.4) 2 - (71.2)(127.1) A =r = 193.2. :gm 2(103.4) - (71.2) - (127.1) This calculated value for the maximum y i e l d i s only four grams higher than the average of the highest yields obtained in the experiment. When one considers the inherent varia tion i n the raspberry suckers, even i f carefully selected, these values are i n f a i r agreement. The Proportionality Constant, c It i s desirable now to compare,the obtained y i e l d curve with a true logarithmic curve, i n order to estimate the conformity of the experiment to the Mitscherlich y i e l d law. Since the maximum y i e l d , A, and the minimum y i e l d , y Q, (yi e l d from the check pot) are already determined for the true curve, i t remains to fin d which one of the possible logarithmic curves that could f i t between these points,best suits the shape of the obtained curve. That Is to say, i t remains to determine the slope of the curve between the maximum and the minimum. As already pointed out, this slope is determined by the proportionality constant of the -20- Mitscherlich y i e l d r e l a t i o n and this i s found by solving eauatlon (VI). Owing to the great variation i n the yields obtained, each set of values applied to the equation result ed i n a different value for the proportionality constant. This rendered the use of equation (VI) unsatisfactory. In order to avoid this d i f f i c u l t y , a series of calculations were carried out on a group of numbers between 0,5 and 1,0 u n t i l i t was found that a proportionality constant of 0.74 resulted i n a curve that closely approximated the curve of the obtained yields (Figure 2). The F e r t i l i t y of the Sand-peat Mixture Before proceeding with the calculations for the theoret i c a l yields indicated by the true logarithmic curve, i t i s necessary to f i n d the i n i t i a l nitrogen content of the sand- peat mixture. This can be determined by solving for b i n equation (VII). logA - log(A-y Q) Equation (VII) i s b = The data are, A = 193.2 gm (the maximum yield ) y Q= 36.4 gm (the y i e l d where no nitrogen was added) c = 0.74 . ( t h e proportionality constant) Substituting, . i:, log(193.2) - log(193.2 - 36.4) b = 0.74 -21- b = 0.12 gm nitrogen per pot This i s the amount of nitrogen that was o r i g i n a l l y present i n the sand-peat mixture as dtermined by the Mitscherlich method of s o i l testing. Calculation of the Yields for a True Logarithmic Curve Having obtained the above information, the theoretical yields Indicated by the true logarithmic curve which has the same slope (c = 0.74) as the obtained curve, may now be c a l  culated and plotted i n order to see how closely the experi ment conforms to the Mitscherlich y i e l d law. Equation (V) which includes the value for b i s used. log(A-y) = logA - c(x + b) For example, when A = 193.2, c = 0.74, b = 0.12, x = 0.12 and y i s the y i e l d which should normally have resulted from i t , then log(193.2 - y) = logl93.2 - 0.74(0.12+ 0.12) y = 67.0 gm In this manner, a l l of the yields which theoretically should have been obtained from the seven treatments were calculated. The results are tabulated i n Table 2, and are expressed both i n grams dry matter and i n percent of the maximum y i e l d (193.2 gm). -22- Table 2. Comparison of Obtained Yields and Theoretical Yields of Raspberry Plants Nitrogen Applied Grams Dry Weight Percent Maximum per pot (gm) Calculated Yields Obtained Yields Calculated Yields Obtained Yields Check 35.3 36.6 18.3 18.8 0.12 67.0 57.8 34.7 29.9 0.33 103.4 107.9 53.5 55.8 0.54 130.4 110.7 67.5 57.3 0.67 142.9 117.2 74.0 60.7 1.34 177.1 139.3 91.7 72.1 2.01 188.1 189.3 97.4 98.0 From Table 2, and p a r t i c u l a r l y from Figure 2 which contains this data, i t i s clear that the obtained y i e l d curve follows the general increase expected i n a Mitscherlich t r i a l , but i t obviously deviates from the logarithmic curve i n three:ofethe seven treatments. Accord ing to Figure 2, a 50% y i e l d of raspberry plant: was obtained when the nitrogen l e v e l was 0.4 gm per pot (0.06 gm per kilogram of s o i l ) . In Figure 2, the y i e l d data expressed as percent of the maximum y i e l d i s plotted against the t o t a l s o i l nitrogen, (x+b) of each treatment. -23- too 7ita/ Soil Nitrojen , (x + b), jrams Figure 2, The Effect of Varying Nitrogen Levels on the Total Dry Weight of Raspberry Plants Compared with a True Logarithmic Curve -24- Results of Raspberry Analysis The results of the analysis are expressed both as t o t a l content per raspberry plant and as percentage composition in Tables 3 and 4, respectively. The t o t a l content per plant i s also represented graphically i n Figure 3. Table 5. Total Nutrient Content per Raspberry Plant. (each figure i s an average of four replicates) Nitrogen Treatment (gm) Nitrogen (N) (gm) Phosphate {P2O5) (gm) Potash (K 20) (gm) Check 0.232 0.117 0.238 0.12 0.438 0.214 0.565 0.33 0.860 0.417 0.934 0.54 0.895 0.415 0.947 0.67 0.944 0.461 1.022 1.34 1.116 0.541 1.224 2.01 1.752 0.774 1.565 The t o t a l absorption curves follow the shape of the y i e l d curve very closely (Figure 3). This was not only true for nitrogen but was also true for phosphate and potash as w e l l . That i s , as the nitrogen applications were varied downward to a deficient l e v e l not only the yields and their -25- Flgure 5. The Effect of Increasing Nitrogen Level on the Total Nutrient Absorption In Raspberry Plants -26- nitrogen contents, but also their phosphate and potash con tents deminished, even though these l a s t were supplied at an ample l e v e l i n a l l treatments. The r a t i o of the absorbed nutrients,, therefore remains approximately the same through out the series at 2:1:21. This r a t i o held i n spite of the fact that the nitrogen i n the f e r t i l i z e r applications was varied downward to 1/20 of the highest application. Table 4. Percentage Composition of Raspberry Plants. (each figure i s an average of four replicates) Nitrogen Treatment (gm) Nitrogen (N) (%.) Phosphate ( P 2 O 5 ) (%) Potash (K 20) (%) Check 0.60 0.30 0.70 0.12 0.83 0.41 1.05 0.33 0.80 0.39 0.87 0.54 0.80 0.38 0.86 0.67 0.81 0.39 0.93 1.34 0.79 0.39 0.88 2.01 0.92 0.41 0.82 The most noticeable result shown by the analysis data was the lack of any trend In the percentage composition of the plants r e f l e c t i n g the f e r t i l i s e r treatment which the plants received. That i s , regardless of the size of plant or the state of nutrient unbalance (except i n the check pot) the percentage composition remained approximately constant. The percentage composition of the check plant, where phosphate and potash as well as nitrogen were present i n l i m i t i n g amounts, was, however, d e f i n i t e l y lower than that of the treated plants (Table 5). Table 5. Comparison of Percentage Composition of Treated . and Untreated Plants Composition of 24 Composition of Treated Plants, % Untreated Plant, % N 0.8 + 0.03 0.6 P 20 5 0.4 ± 0.02 0.3 K 20 0.9 ± 0.08 0.7 Although i t i s unfortunate that the check plant was not run i n quadruplicate, the difference between i t s com position and that of the treated plants appears s i g n i f i c a n t . Conclusions on the Raspberry Experiment This experiment supplies additional information to the work of Woods and Harris (14) by showing the quantitative effect of Increasing the nitrogen f e r t i l i z a t i o n . The n i t r o  gen supply was increased u n t i l i t was twenty times the amount of nitrogen o r i g i n a l l y present i n the s o i l . By far the most satisfactory growth was obtained i n the high n i t r o  gen treatment, whereas the growth obtained i n the low nitrogen pot was quite comparable to poor f i e l d plantations, a 50% y i e l d being classed here as d e f i n i t e l y poor growth. The experiment also indicates that there i s a definite amount of nitrogen which w i l l give a certain amount of cane growth.when the other growth factors, including water, are present i n s u f f i c i e n t amounts. For instance, b0% growth i s obtained from a sand-peat mixture when nitrogen i s present at 0.4 gm per pot. In this experiment, therefore, one "food u n i t " i s 0.4 gm nitrogen per pot. Interpreting this i n terms of nitrogen per acre (6" deep), i t amounts to 230 pounds(calculated on a s o i l weight b a s i s ) , which i s i n marked agreement with the recognized Baule unit of nitrogen, 225 pounds per acre (15). From the standpoint of making f e r t i l i z e r recommendations, the most important information shown Is the fact that the best growth was obtained when the nitrogen.was two times higher than the phosphate or potash. In preliminary rasp berry t r i a l s (unpublished) canes were grown successfully i n the greenhouse, with good growth and f r u i t i n g , when the nitrogen was f i v e times higher than the phosphate and 2§ times higher than the potash. Although the t o t a l amount of absorbed nutrients i s pro portional to the increase i n the y i e l d and therefore to the increase i n the s o i l nutrients, the r a t i o of the absorbed nutrients bears no r e l a t i o n to the ratio of the same n u t r i  ents i n the s o i l . This seems to indicate that the t o t a l amounts of the nutrients i n the raspberry plant are absorbed in a d e f i n i t e r a t i o regardless of the state of the nutrient unbalance and size of plant. The apparent constancy of the percentage composition shown i n this work i s not i n accord with the results of the following experiment with oats, nor with the published data of Mitscherlich, P f e i f f e r , Macy, et a l , (6). On the whole the results obtained are s u f f i c i e n t l y indicative to warrant the further use of the Mitscherlich method i n raspberry n u t r i t i o n work, especially with an im proved technique. One material drawback i s the fact that second year growth cannot be measured s a t i s f a c t o r i l y , that i s , i t cannot be measured independent of the f i r s t year's growth. S t r i c t l y speaking, therefore, this method i s con fined to,the f i r s t year's growth, except for qualitative observations, such as the deficiency symptoms, incidence of virus disease, dying of buds, and quality of product. Since the raspberries i n this experiment were only studied for the f i r s t year of growth, observations of this type could not be made. -30- Part I I AN EXPERIMENT WITH OATS Introduction In view of the very moderate success with the raspberry experiment, p a r t i c u l a r l y i n regard to the Mitscherlich growth law, a more extensive experiment with oats was designed. In this experiment, a pear orchard s o i l from the Experi ment Station at Saanichton B.C. was used as the growth medium. The size of pot used was 1/6 the size of that used by Mitscherlich and much smaller and of a different type than that used i n the raspberry experiment. Oats were chosen as the plant Indicator because the genetic variation in the seed i s p r a c t i c a l l y negligable, thus eliminating the greatest source of error that was present i n the raspberry experiment. This experiment was run i n three series (nitrogen, phosphate, and potash) i n order to check the y i e l d law with a l l three nutrient. Since rapid chemical s o i l testing i s a very popular method of evaluating s o i l f e r t i l i t y , special attention was paid i n this experiment to a comparison of the rapid chemical tests with the Mitscherlich plant method of s o i l testing. The analysis of the plant material, as i n the raspberry experiment, was carried out as a check on the y i e l d phenomena and as a study on the re l a t i o n between s o i l f e r t i l i t y and nutrient absorption. -31- Experimental Apparatus . Instead of the large enameled metal pot used by Mitscherlich, Capo, Magistad> et a l , laquered t i n cans of 4" diameter and 4" s o i l depth were used. Their capacity was one kilogram of screened s o i l and they had an area of 12.56 square inches or 0.000002 acre. These pots, 44 of them comprising eleven treatments i n quadruplicate, were placed in a rack arranged so that small laquered t i n cans could be placed under them to act as drainage pans. The pots were provided with a central drainage hole. Wire supports were provided for the plants. S o i l Samples S o i l samples were taken from half an acre of a gravely loam pear orchard s o i l at the Dominion Experiment Station at Saanichton, B.C. Sixteen samples, amounting to approximately 150 pounds of s o i l , were taken to a depth of 8 inches with a spade. This was screened i n a -J- inch riddle and, from the weight of screenings, the s o i l was found to be approximately 20% stones. A sample of s o i l was kept for analysis. From the apparent spe c i f i c gravity, the acre weight of this s o i l was determined as 2 m i l l i o n pounds. Mixing Procedure The screened s o i l was thoroughly mixed i n a galvanized -32- iron tub. Eight kilograms of this were weighed out in an enamel basin. The approximate amounts of stock solutions for one of the treatments were then pipetted into the s o i l , care being taken; not to spray i t on the sides of the basin. The s o i l was then thoroughly mixed by hand, making sure a l l moist lumps were broken up. I t was then divided into four equal parts by weight and transferred to the pots which were then labeled as the four replicates of a single treatment. Each of the eleven treatments was mixed In this manner. The bottom 3 to 4 centimeters were tamped down and the top s o i l l e f t r e l a t i v e l y loose. The replicates were staggered on the rack so that none were adjacent. Plant Material and Stand Victory oats (s/2, 1940) were treated with CU2CO3 dust. Seeds were selected to a uniform size and were planted to a depth of 1.5 centimeters, 12 In each pot. The s o i l was moistened with d i s t i l l e d water and covered with a sheet of heavy wax paper u n t i l germination was completed. At the second leaf stage (August 9, 1941), they were thinned out to 6 plants per pot, care being taken to remove seeds i n the operation (forceps were used). Watering When i t appeared necessary, the pots were brought as nearly to saturation as possible without overflowing to the -33- drainage pan. I f the pots were accidentally flooded, the water was returned from the drainage pans to their respective pots before the next watering. Care was taken to avoid over watering i n order to guard against poor a i r a t i o n . D i s t i l l e d water was used. Watering was discontinued a week before the harvest. Control of Conditions The experiment was carried on i n a r e l a t i v e l y cool green house at the Experiment Station. For the f i n a l two weeks i t was removed to a warmer house i n order to hasten maturity. The plants were dusted several times with sulphur and were sprayed once with nicotine sulphate for the control of aphids. They were also dusted once with a lead arsenate-nicotine dust to control chewing insects. Feeding Plan and Stock Solutions The experiment had three series (nitrogen, phosphate, and potash). In each series a l l growth factors were supplied at an ample l e v e l except the variable, which was varied down ward i n equal Increments to a zero application. The ample levels i n this experiment were chosen as one Baule unit of each, that i s , 225 pounds nitrogen, 45 pounds ^2Qb* a n d 8 2 pounds K 20 per acre. The amounts per pot were calculated from this on an area basis. The general plan was as follows: -34- Table 6 Feeding Plan of Oat Experiment Series Pot Number Nitrogen (gm) P 20 5 (gm) K 20 (gm) A l l high 1 0.204 0.039 0.075 2 0.136 0.039 0.075 N 3 0.068 0.039 0.075 4 0.000 0.039 0.075 5 0.204 0.026 0.075 P2O5 6 0.204 0.013 0.075 7 0.204 0.000 0.075 8 0.204 0.039 0.050 K 20 9 0.204 0.039 0.025 10 0.204 0.039 0.000 Check 11 0.000 0.000 0.000 In Table 6 the " a l l high" pot receives the greatest amount of each of the growth factors and was, therefore, the top pot for each of the series. The nitrogen was supplied as (NH^)gS04 a n d NaW03 i n such proportion that half the nitrogen was supplied by each s a l t . The amounts of the salts used are represented by the following values for the ''al l high" pot. -35- Table 7. Salt Weights of the Highest Applications. • Unit (NH 4) 2S0 4 Sup e r pho s pha te 18$ K 2S0 4 gm per pot 0.48 0.62 0.21 0.14 lbs per acre 530 682 250 150 The nitrogen stock solution was made up by dissolving 17.28 gm (BH4-)gS04 and 22.32 gm NaN03 In water and making i t up to 270 ml. Then 30 ml contained 4 units; the amount required for the maximum application for 4 pots (replicates). Thus 20 ml contained enough for the 2/3 unit l e v e l for 4 rep l i c a t i o n s , and 10 ml contained enough for the 1/3 unit l e v e l for 4 replications. Using Mitscherlich's procedure^or dissolving super phosphate (13), 8.28 gm of i t were dissolved and administered as above. In the same manner, 5.04 gm K2S0 4 were d i s t r i b  uted. Harvest Methods The height of the tops were measured. The heads were stripped o f f , the straw cut off at the ground, and the roots were washed clean. Green weights of the straw and grain were obtained. The number of stalks were also counted. The material was dried i n an oven at 90*0 for 24 hours. Dry -36- weights of roots straw and grain were recorded separately. The growing period was 127 days from August 3, 1941 to December 7, 1941. The material was ground to a powder and stored i n en velopes for analysis. Methods of Analysis The s o i l samples were analysed by means of the rapid chemical tests of Spurway (12) and Morgan (10). The t o t a l phosphate content of the s o i l was determined by the A.O.A.C. method (1) modified for use with Tschopp's colorimetrie method and the B.D.H, standard color discs (3). The plant material was analysed for t o t a l nitrogen, phosphate, and potash. The nitrogen analysis was carried out with the Kjeldahl method (1) using one gram samples. For phosphates, the 0.3 gram samples were digested In per chloric acid, neutralized, and the determination carried out by Tschopp's method as modified for use with the B.D.H. Nesslerizer color discs,(3). The potash was determ ined by the S h e r r i l l method (11) on the ash solutions obtained from one gram samples. Results of the Oat Experiment Dry Weight Data The following tables and graphs are composed of the measurements made on the growth of the plants and indicate -37- the trend of the results which w i l l he discussed i n greater d e t a i l l a t e r . The dry weights given i n Table 8 include the weights of the roots, straw, and grain. Table 8. Total Dry Weight of Oats Resulting from Dlfferen t i a l F e r t i l i z i n g with Nitrogen, Phosphate, and Potash. Treatment (gm) Replications Average N — 0.204 .1.;. P2°5 — 0.039 11.5 10.6 9.6 10.2 10.5 + 0.8 K 20 --0.075 0.136 11.6 10.5 11.1 10.1 10.8 0.7 N 0.068 10.6 9.4 10.0 10.0 10.0 + 0.5 0.000 4.9 4.6 4.9 4.6 4.75 ± 0.2 0.026 11.6 11.9 11.6 10.5 11.4 + 0.3 P2°5 0.013 12.4 9.7 10.7 11.5 11,1 1.1 0.000 11.5 10.9 11.1. 11.2 11.2 ± 0.2 0.050 11.1 10.9 9.8 10.5 10.6 + 0.6 K 20 0.025 10.9 10.7 10.6 10.6 10.7 ± 0.1 0.000 10.7 10.7 10.4 10.2 10.5 + 0.2 Check (0-0-0) 4.6 4.5 4.4 4.5 4.5 ± 0.1 Standard deviation = /i=L£il / -71- / 38- The data given i n Table 8 are graphically represented In Figures 4, 5, and 6. A l l of the measurements made on the oats r e f l e c t the same trends as do the t o t a l dry weights. For the sake of s i m p l i c i t y , therefore, only t o t a l dry weights of the oat plants are reported. I t i s noteworthy that the replicates i n a l l treatments agree very closely, having an average standard deviation of 0.4 grams for the eleven treatments. No single treatment shows a standard deviation greater than 1.1 grams (Table 8). The nitrogen series shows a general Increase In y i e l d , indicating a good response to nitrogen f e r t i l i z a t i o n (Table 8 and Figure 4). Both the phosphate:-and the potash series show no general increase In y i e l d , Indicating that there i s no positive response to f e r t i l i z a t i o n with these elements (Figures 5 and 6). The' " a l l high" treatment, which received the greatest amount of each of the growth factors and which was the high est treatment for each of the three series, unfortunately gave a lower y i e l d than was expected, especially i n respect to the nitrogen and phosphate series. This appeared to be due to excess nitrogen, judging by the dark green color of the leaves, much branched habit, shorter straw, and low grain formation. I t i s u n l i k e l y , however, that i t was due to excess nitrogen alone, because a l l of the pots i n both phos phate and potash series received the same high amount of -40= nitrogen(0.204 gm nitrogen per pot). In spite of t h i s , the phosphate series showed the highest yields i n the experiment and neither the phosphate or the potash series showed any excess nitrogen symptoms. A l l pots of both the nitrogen and potash series, as well as the high phosphate treatment of the phosphate series, re ceived P2°5 &t 0.039 grams per pot. However, the remainder of the phosphate series, which a l l received less than 0.039 grams P 20g per pot including the treatment which received no phosphate, consistantly gave yields that were one gram higher than any other treatment i n the experiment. An important point revealed by the data of Table 8 i s the lack of a s i g n i f i c a n t difference between the "no nitrogen" treatment which received phosphate and potash f e r t i l i z e r , and the check treatment which received no f e r t i l i z e r at a l l . Since the phosphate and potash series showed no measure- able response, i t was not possible to make calculations on these series. Calculations for the nitrogen series were, however, carried out. The Maximum Possible Y i e l d Since the nitrogen curve exhibits a decline at the high end of the series, the calculated value for the maximum y i e l d (10.9 gm) i s s l i g h t l y lower than the highest average y i e l d (11.4 gm). I t seemed wise, therefore, to use 11.4 grams as the maximum y i e l d , although i t makes l i t t l e difference to the calculations. -41- Proportionality Constant When no nitrogen was added to a pot, a y i e l d of 4.75 gm was obtained. This was the result of an amount of nitrogen, b, which was i n the normal s o i l . The whole y i e l d curve was therefore, displaced upwards by an amount of 4.75 gm. The f e r t i l i t y of the s o i l i s then represented by, x+b, which includes both the o r i g i n a l f e r t i l i t y , b, and the known f e r t i l  izer,: x. This term, i t w i l l be remembered, i s included i n equation (V) which i s log(A-y) = logA- c(x -t- b ) Since both b and c were, as yet, unknown quantities i n this equation, two such equations were solved simultaneously using the condensed form (VI) which i s log(A-yx) - l o g ( A - y 2 ) C = '. v. . . •/• "/\ x2 ~ *1 Since A was 11.4, y 1 was 4.75, y 2 was 10.0, x i was 0.000, and x 2 was 0.068, then log(11.4 - 4.75) - log(11.4-10.0) c = '. 0.068 ~ 0.000 c — 10 This means that the value of the proportionality constant -42- which i s characteristic of the slope of the curve obtained i n the nitrogen series of this experiment was 10. Use i s made of this number i n the following calculations for the s o i l nitrogen and the yields for a true logarithmic curve. S o i l Nitrogen The amount of nitrogen already present i n the pot was then calculated from equation-(VII) where y Q i s the y i e l d obtained when no nitrogen was added to the s o i l . logA - log(A-y 0) b = • i ; C l o g l l . 4 - log(11.4 - 4.75) b =. — — — — : — 10 b = 0.023 gm nitrogen per pot According to the Mitscherlich method, therefore, this s o i l contained 23 mg nitrogen per kilogram of screened a i r dry s o i l . Calculations of the Yields for a True Logarithmic Curve It was desirable then to check the v a l i d i t y of the Mitscherlich s o i l test. This was accomplished by computing a true logarithmic curve between the maximum (11.4 gm) and the minimum (4.75 gm) of the same slope as the obtained y i e l d -43- curve (c = 10). The purpose of this operation was to estimate the accuracy of the experiment by finding how closely the observed curve resembles a true logarithmic curve. Having determined the value for the maximum y i e l d , A; the s o i l f e r t i l i t y , b, or x+b as the case may be; and the proportionality constant, c; the theoretical yields for each treatments were then calculated by means of the general equation (V). The results of these calculations are given in Table 9, both i n terms of grams dry weight and as percent of the maximum (11.4). Table 9. Comparison of Observed Yields and Calculated Yields of Oats. Kitrqgen Supplied • (gm) Grams Dry Weight Percent of Maximum Observed Calculated Observed Calculated 0.204 10.5 11.4 92.1 100.0 0.136 10.8 11.1 94.7 97.3 0.068 10.0 10.0 87.8 87.8 0.000 4.75 4.7 41.7 41.2 The data of Table 9 Is represented graphically i n Figure 7. From Table 9 and Figure 7 i t may be seen that the obser ved yields of the nitrogen series follow the shape of a true -44--45- logarlthmic curve very closely, excepting for the slight decline at the high end of the series. From Figure 7, a 50% y i e l d of oats was obtained i n this series when the available nitrogen was present in the s o i l at 28 mg per kilogram, and an 87.8% y i e l d was obtained with 91 mg nitrogen per kilogram of screened a i r dry s o i l . Results of Chemical S o i l Tests The s o i l sample was f i r s t tested with the Spurway method of s o i l testing (12). In these tests (Table 10), 2.5 gm s o i l were diluted to 13.5 ml with weak acetic acid extracting solution. The p.p.m. refer to the concentrations i n this solution. The amounts per pot were calculated for one k i l o  gram of s o i l , the amount of s o i l used i n each pot. Table 10. Spurway Extract Analysis. Nutrient p.p.m. gm per pot 0.016 0.005 0.042 In view of the results obtained from the Mitscherlich test, i t was f e l t certain that the values for phosphate and Nitrogen (N) 3 Phosphate (Pg0 5) 1 Potash (KoO) 8 -45- potash were far too low. Further analysis was therefore carried out, this time using the strong action of Morgan's sodium acetate-acetic acid mixture (10) as the extracting agent. In these tests (Table 11), 5.5 gm s o i l were diluted to 13.5 ml (twice as concentrated as the Spurway extract). Table 11. Morgan Extract Analysis Nutrition p.p.m. gm per pot Nitrogen (N) 6 0.016 Phosphate (Pg0 5) 2 0.005 Potash (K 20) 24 0.060 Tables 10 and 11 show a close agreement on a "low" nitrogen content (16 mg per kilogram) and on a low phosphate test (5 mg per kilogram) but they do not agree on the potash test. This was to be expected because the Morgan extracting solution frees potassium from the base exchange complex. The s o i l was rather high i n available iron (40-50 mg per kilogram).and consequently i t had a rather high phosphate f i x i n g power. The t o t a l phosphate content of the s o i l , estimated by fusion with sodium peroxide, was 2.54 gms P 20 5 per kilogram. -47- Resuits of the Plant Analysis The results of the analysis of the oat plants i s presented i n Table 12 i n terms of t o t a l absorption of n u t r i  ents per pot (six oat plants) and i s expressed as averages of the four replicates. Table 12. Analysis of Oats as Total Nutrient Absorption per Pot (Each figure i s the average of four replicates) Treatment Total N Total PoOg Total K 20 (gm) (gm) (gm) (gm) A l l high 0.170 0.047 0.234 0.136 N 0.068 0.000 0.026 P 20 5 0.013 0.000 0.050 K 20 0.025 0.000 0.127 0.081 0.027 0.166 0.164 0.163 0.163 0.160 0.160 0.049 0.045 0.021 0.051 0.050 0.050 0.048 0.048 0.047 0.223 0.228 0.123 0,217 0.240 0.219 0.214 0.187 0.197 Check 0.025 0.020 0.126 O .Obr -13k -Z09 O -Oil -0Z(, ,0V) O .OZf .OS-O .o>i' Grams /V jaer }?ot Grains PxO\r per f>ot Grams HzO per j>ot Figure 2. Nitrogen Series f^ure 9. Phosphate Series Figure 10. Potash Series -49- The data of Table 12 i s represented graphically i n Figures 8, 9, and 10. When Figures 4, 5, and 6 are compared with Figures 8, 9, and 10, i t w i l l be seen that the t o t a l nutrient absorption i n each series followed rather closely the shape of the corresponding y i e l d curves. The nitrogen, phos phate, and potash absorbed i n the nitrogen series show curves similar i n shape (Figure 8) regardless of the fact that the nitrogen was the only nutrient varied i n supply. I t should be noted however, that the nitrogen absorption curve of the nitrogen series continued to r i s e after the phosphate and potash curves had leveled out In accordance with the y i e l d curve. When the nitrogen, which was i n the minimum, was raised to an-excess,, extra absorption of nitrogen occurred, A similar phenomenon occurred i n the potash series. The absorption curves of the potash series,resemble the y i e l d curve with 1the exception of the potash l i n e (Figure 10), Although no excess potash symptoms were observed i n the plants, they never-the-less underwent extra absorption of potash as the potash supply was increased. The absorption curves of the phosphate series a l l re semble the phosphate y i e l d curve. No extra absorption of phosphate occurred. When the nutrient absorption was studied i n conjunction with the manurial content of the pots, some evidence was obtained for the mass action theory of plant growth. In order -50- to get the correct nutrient absorption figures i t was found necessary to subtract the amount of nutrient supplied by the seed. The average analysis of si x seeds, weighing 0.25 gm, was 4 mg nitrogen. Table 13. Percent S o i l Nitrogen Absorbed Compared with the Y i e l d Total S o i l N- (x+b) (gm) Total Plant N (gm) Plant N minus Seed N (gm) # S o i l N Absorbed % Y i e l d 0.023 0.027 0.023 100 41.7 0.091 0.081 0.077 85 87.8 0.159 0.127 0.123 77 94.7 0.227 0.170 0.166 73 92.1 Prom Table 13 i t i s apparent that as the f e r t i l i z e r was increased by unit increments, i t became less and less e f f i c  ient at producing an increase i n y i e l d . In the "no nitrogen" treatment, a l l of the nitrogen i n the s o i l was taken up by the plants, but, as the nitrogen was stepped up by unit incre ments, the nitrogen going into the plants and the yields went up by diminishing increments. At the higher end of the series i t required a greater and greater nitrogen reserve i n the s o i l to produce a smaller and smaller increase i n y i e l d . N O O n <u P -c 42 o Q-. 0; K 3 -52- The s o i l analysis figures for the phosphate and potash were less r e l i a b l e and could not be considered i n this connection. The percentage composition of the plants (Figures 11, 12, and 13) showed the same trends as the t o t a l absorption curves, with the exception of the percent potash i n the plants of the nitrogen series. Although the t o t a l potash increased with the y i e l d , the concentration of potash i n the plant stayed at a high l e v e l and even decreased s l i g h t l y from 2.6% to 2,05$ at the maximum y i e l d and then Increased s l i g h t l y In the de pressed y i e l d of the high nitrogen pot, (Figure 11). The phosphate determinations were not sensitive enough to detect small differences i n phosphate concentration i n the plants. Conclusions on the Oat Experiment Although the results of the phosphate and potash series showed no y i e l d response and consequently were not applicable to the Mitscherlich equations, the nitrogen series demonstrat ed the application of Mitscherlich's growth laws to the yields of systematically grown oat plants. The fact that the average standard deviation of eleven treatments was only 0.4 grams, with a maximum standard deviation of 1.1, i l l u s t r a t e s the accuracy that may be obtained. The comparison of the obtained y i e l d curve of the nitrogen series with a true logarithmic curve of the same slope (c = 10), shows that the calculations -53- for s o i l nitrogen are dependable. D i f f i c u l t y was encountered i n trying to find a satisfac tory explanation of the decline i n y i e l d at the high end of the nitrogen and phosphate series. Although this " a l l high" treatment showed excess nitrogen leaf symptoms and underwent extra absorption of nitrogen (Figure 8), none of the lower phosphate and potash series treatments which received the same high amount of nitrogen (0.204 gm) showed excess nitrogen leaf symptoms even though they showed the same high nitrogen content (Figure 9 and 10). On the other hand, a l l of the low phosphate treatments showed higher yields than a l l the other treatments which received the highest phosphate application (0.039gm). The lack of response i n the phosphate and potash series indicates a p l e n t i f u l supply of both these nutrients i n the s o i l . This conclusion i s supported'by the lack of si g n i f i c a n t difference between the "no nitrogen" treatment and the check treatment. From the nitrogen y i e l d curve, i t can be d e f i n i t e l y stated that a certain quantity of nitrogen i s equivalent to a def i n i t e y i e l d of oats. That i s , when available nitrogen Is present i n this s o i l at 28 mg per kilogram, a 50$ y i e l d may be expected In a pot culture. When the nitrogen l e v e l i s 91 mg per kilogram, an 88$ y i e l d w i l l be obtained. . In this experiment, therefore, one "food unit" i s 28 mg nitrogen per pot. Interpreting this i n terms of nitrogen per acre -54- (6" deep), i t amounts to 56 pounds (calculated on a s o i l weight basis). This i s only \ of the recognized Baule unit of nitrogen, 225 pounds per acre (15). Tables 10 and 11, and the results of the Mitscherlich method show that the chemical tests for nitrogen agree closely with each other at 16 mg nitrogen per kilogram of screened a i r dry s o i l , and that they check within 7 mg with Mitscherlich method (23 mg per kilogram). The higher value obtained by the plant method may be accounted for by the fact that this method takes into account the nitrogen that was fixed and re leased by microbiological a c t i v i t y during the growth period. Since calculations were impossible with the phosphate and potash series, no direct comparison with the rapid chem i c a l tests can be made. However, certain conclusions can be drawn on the basis of the plant analysis. The absorption of 197 mg of potash into the plants which received no potash f e r t i l i z e r indicates that at least 197 mg of potash were vailable to the oat plants during the period of growth. A l  though no y i e l d response was obtained with potash f e r t i l i z e r s , extra absorption of potash occurred (up to 37 mg extra) when potash f e r t i l i z e r was added. I t i s most probable, therefore, that more than s u f f i c i e n t potash was available than was re quired for a maximum y i e l d . The chemical tests for potash appear to be far too low (42-60 mg per kilogram). This may be p a r t i a l l y explained by the fact tha't the plants take into -55- account the potash which becomes available from mineral de composition during the growing period. I t i s also possible that the plants made use of base replaceable potassium. The chemical tests for phosphate (5 mg per kilogram) are too low with respect to the plant analysis results. The analysis of the plants of both the "no phosphate" and the check treatments shows that at least 20 mg of phosphate must have been available to the plants. Although the chemical test shows the amount of phosphate that i s available at any one time, i t offers no idea as to the rate at which I t become available during the l i f e of the plant, nor does i t estimate the t o t a l amount that i s l i k e l y to become available during that time. The t o t a l phosphate content of the s o i l offers no clue to the problem. From a plant y i e l d viewpoint, therefore the rapid chemical tests for phosphate are wholly unsatisfac tory. However, i t i s possible that.as long as the phosphate becomes available at the same rate that i t i s used, and i s at a l l times available at 5 mg per kilogram, the plants w i l l make satisfactory growth. This experiment does not preclude that better growth could not have been obtained i f the phos phate had become available at a higher rate. The analysis of the plant material i s useful largely as a check on the conclusions drawn from the y i e l d curves. In this experiment with oats, for example, Important Information has been gained on the extra absorption of nitrogen and -56 potash, and, as already pointed out, the figures on t o t a l nutrient absorption i n the check treatments served as an im portant check on the s o i l analysis data. The r e l a t i o n between s o i l f e r t i l i t y , nutrient absorption and plant y i e l d has been demonstrated. As the nitrogen f e r t  i l i z e r i s stepped up by unit increments, both the absorption of nitrogen and the yields go up by deminlshing increments. Furthermore, when the f e r t i l i t y i s low, the y i e l d i s also low but the plants take p r a c t i c a l l y a l l of the nitrogen from the s o i l . As the nitrogen f e r t i l i t y l e v e l i s raised, the yields increase by deminlshing increments and i t takes a greater and greater nutrient "reserve" i n the s o i l to produce a smaller and smaller increase i n y i e l d . This fact has an important bearing on the costliness of o v e r - f e r t i l i z a t i o n . Thus, 91 mg nitrogen gave an 88$ y i e l d , but i n order to gain 7$ i n y i e l d over t h i s , the nitrogen i n the soil/had to be doubled to 180 mg per pot. Running the ris k s of excess f e r t i l i z a t i o n , i t i s doubtful i f this small increase i n y i e l d would pay for the extra f e r t i l i z e r . The plant analysis, expressed as percentage compostion, proved r e l a t i v e l y uninformative as compared to the t o t a l com position of the plants. -57- General Conclusions on the Application of the Mitscherlich Method to Raspberries and Oats The general conformity to the Mitscherlich growth law exhibited by both the raspberries and the oats, as well as the information gained on s o i l f e r t i l i t y and the n u t r i t i o n of these plants, certainly warrants more extensive use of the Mitscherlich method. Although these two experiments differed i n plant type, s o i l texture, size and type of pot, l o c a l i t y , and year, they are d i r e c t l y comparable. This seems scarcely possible when It i s remembered that the values obtained i n the two experi ments differed greatly i n magnitude: Raspberries Oats Proportionality constants 0.74 10 "Food units" of nitrogen 0C4 gm 0.028 gm Maximum yields 193.2 gm 11.4 gm Ne T e r_the-less, these results are proportional to one another In the following manner: 0.74 0.028 11.4 _ • • •.—: - — 10 0.4 193.2 0.07 °C 0.07 aC 0.06 -58- As a result of these computations, we may say that, °1 x 2 A 2 C2 x l A l where the subscript 1 indicates the values from the raspberry experiment and subscript 2 indicates the values from the oat experiment. The fact that this r e l a t i o n holds, demonstrates that the Mitscherlich law i s fundamental and remains v a l i d regardless of plant species, s o i l class, or atmospheric con dit i o n s . From this general v a l i d i t y , therefore, i t i s con cluded here that, although most of the attention paid to the Mitscherlich method i n the past has been concerned with i t s value as a s o i l testing agent, i t also presents a standard ized basis for carrying out comparable plant n u t r i t i o n experiments. The evaluation of nutrients In /terms of plant yields by means of pot t r i a l s , however, s t i l l presents some important problems. One "food unit" In the raspberry experiment was found to be 60 mg nitrogen per kilogram of a i r dry s o i l , whereas one "food unit" i n the oat experiment was 28 mg n i t r o  gen per kilogram of s o i l . These experiments provide l i t t l e grounds for an explanation of this difference. I t must be pointed out, however, that i n the oat -experiment llf;4:. gm of plant material grew on one kilogram of s o i l , whereas in the raspberry experiment 193.2 gm of plant material grew on only -59- 6.5 kilograms of s o i l . This difference i n "food unit" results may he due to a difference i n crowding effect. In future experiments of this sort, the r e l a t i o n of pot size to plant size should be taken into account more carefully In order to make the experiments more comparable. Since the acre weights of the two s o i l s differed by 1,764,000 pounds, the breach between the Baule unit determin ations i s widened s t i l l further when calculations are made on an acre basis. Thus, one Baule unit as determined by the oat experiment was 56 pounds of nitrogen per acre, whereas one Baule unit as determined by the raspberry experiment was 230 pounds of nitrogen per acre. The l a t t e r figure checks . s a t i s f a c t o r i l y with the proposed Baule unit of 225 pounds of nitrogen per acre. I t i s suggested that experiments with different sizes of pots i n conjunction with a f i e l d t r i a l on the same s o i l be used as an approach to this problem. In regard to the making of f e r t i l i z e r recommendations, an important feature of these investigations i s the fact that the best growth i s obtained when the available s o i l nitrogen is much higher than the available phosphate and potash. The evidence obtained tends to support the Mitscherlich ratio 5:1:2 as the optimum balance for s o i l nutrients. The amount of space, time and equipment required for the plant method, however, eliminates i t as a p r a c t i c a l routine method for testing large numbers of s o i l s , although i t would -60- be of considerable value to B r i t i s h Columbia agriculture I f It was known how the different s o i l types and classes from the different agriculture d i s t r i c t s responded to the Mitscherlich treatment. I t i s concluded here also that more extensive use of the plant method i n conjunction with chemical tests, may lead to the adoption of more r e l i a b l e chemical tests and may also serve to give the results of chemical test ing a quantitative meaning i n terms of plant y i e l d . I t i s also concluded that the analysis of the plant material gives important supporting information to the results of the Mitscherlich method. -61- Blbllography (1) A.O.A.C. O f f i c i a l and tentative methods. (1936) (2) Baule B. Zu Mitscherlich'sGesetz der physiologischen Beziehungen. Landwirtschaftlich Jarbucher, Bd 51: 363-385. (1918) (3) B r i t i s h Drug Houses, Lovibond Nesslerizer colorlmetric methods and standard color discs. (4) Capo' B.G. A modification of Mitscherlich's method for the determination of the nutrient contents of a s o i l . Jour. Agric. Univ. Puerto Rico, 2(2): 137-169. (1938) (5) Hartung W.G. The Mitscherlich method of s o i l testing and Interpretation of results. The Hawaiian Planter's Record, 33(4): 439-448. (1929) (6) Macy P. The quantitative mineral nutrient reauirements of plants. Plant Phys., 11: 749-764. (1936) (7) Magistad O.C. Comparison of Mitscherlich t r i a l s on Hawaiian s o i l s i n Germany and i n the Territory of Hawaii. Jour. Amer. Soc. Agron., 30: 692-698. (1938) (8) Mitscherlich E.A. Die Bestimmung des Duengerbedurfnisses des Bodens. (3rd Ed.) Paul Parey, Berlin.(1930) -62- (9) Mitscherlich E.A. "Uber das G-esetz des Minimums und die sich aus diesem ergebenden Schlus sfolgerungen. Landwirtschaftlich Versuchs-Stationen, Bd 75: 231-263. (1911) (10) Morgan M.F. S o i l testing methods. Conn. Agric. Exp. Sta. Tech. B u l l . 392 (11) S h e r r i l l E. Centrifugal method for determining potash. Jour. Ind. Eng. Chem. Vol 13, No. 3: 227-228. (March, 1921) (12) Spurway C.H. S o i l testing. Mich. Agric. Exp. Sta. Tech. B u l l . 132 (2nd revision). (1938) (13) Stewart R, The Mitscherlich, Wiessmann, and Neubauer methods of determining the nutrient content of s o i l s . Imp. Bur. S o i l Sc. Tech. Comm. 25 (1932) (14) Report of the B r i t i s h Columbia Raspberry Committee (1935- 41). B r i t i s h Columbia Department of Agriculture. (15) Willcox O.W. ABC of Agrobiology. W.W.Norton, N.Y.(1937) 

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