usually limiting the assimilation metabolism GILBERT · THE CURRENTMINERALNUTRIENT CONTENTOF THEPLANT SOLUTIONASANINDEXOFMETABOLIC LIMITING CONDITIONS* B. E. GILBERT, F. T. MCLEAN

THE CURRENT MINERAL NUTRIENT CONTENT OF THE PLANTSOLUTION AS AN INDEX OF METABOLIC LIMITING

CONDITIONS*

B. E. GILBERT, F. T. MCLEAN ANXD W. L. ADAMS

(WITH SEVEN FIGURES)

IntroductionThe rate of metabolism at any time during the life of a plant is usually

governed by one or more limiting conditions. These conditions limitingmetabolism may be either chemical or physical in nature; either a limitingsupply of raw materials for metabolism or some condition due to the physi-cal state of the soil, or atmosphere which interferes with the assimilationand elaboration of these raw materials. In this paper attention is drawnto three cases of inhibited metabolism and the accompanying effects on thecurrent mineral nutrient content of the plant solution during 1926. Theconditions which were seemingly responsible for decreased metabolism were:

1. A decreased supply of available manganese in a neutral soil, result-ing in a marked chlorosis in beets and spinach.

2. Limiting amounts of phosphoric acid and nitrogen as supplied to thesoil in fertilizers.

3. Unfavorable weather or cultural conditions.

Analytical methodsThe methods discussed by GILBERT in an earlier publication (2) were

followed with certain changes of procedure. It was found that when theplant solution was heated to 800 C. before filtering, flocculation took placeand filtration was facilitated. Further work with the calorimetric methodfor potassium led to the adoption of the LINDO-GLADDING gravimetricmethod. This change was made due to the labor and time involved inrecovering the waste platinum from the colorimetric method and also fromthe fact that by the gravimetric method it was found possible to determineaccurately the amounts of potassium usually found in the plant solution.

A limiting available manganese supplyFor many years the Rhode Island experimental plats have grown crops

which from time to time were distinctly chlorotic. It has been found that* Contribution no. 345 of the Rhode Island Agricultural Experiment Station, Kings-

ton, R. I.139

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PLANT PHYSIOLOGY

this chlorosis occurs only with plants growing on soils which have been neu-tralized, and recently the correction of the conditions has been brought aboutby small applications of manganese salts in a spray (3), or as a fertilizermixed with soil. Chemical determinations of the leafy tissue of crop plantshave shown smaller amounts of total manganese in the chlorotic tissue thanin the normal healthy green tissue (3). These results have led investi-gators to conceive the available manganese supply in the neutral or alkalinesoil to be limiting and insufficient for normal metabolism. This conditionproved to be most pronounced when coupled with a low nitrogen fertiliza-tion.

Plant solution determinations were made to compare the nutrient ele-ment levels in the chlorotic and non-chlorotic plants. In table I a compari-son is given of the manganese fertilization and the nitrate-nitrogen as foundin the plant solution.

TABLE ICOMPARISON OF NITRATE-N CONTENT OF PLANT SOLUTION AND MANGANESE FERTILIZATION

FERTILIZATION CONDI- NITRATE-NCROP TISSUE PLAT (LBS. PER ACRE) TION OF IN PLANT SOLUTION

N< PA0_ KO Mn. PLANTS P. P. M.

June 2Spinach Leafy 21 MG* 0 200 30 11 Green 50Spinach Leafy 21 MG 0 200 30 0 Chlorotic 283Spinach Leafy 50 MG 60 200 30 9 Green 138Beets Leaves

and Sept. 17 Oet. 1 Oct. 8petioles 119 MG 45 120 90 9 Green 59 42 30

Beets Leavesand

petioles 119 MG 45 120 90 0 Chlorotic 176 104 28Beets Roots 119 MG 45 120 90 9 Green 200 283 125Beets Roots 119 MG 45 120 90 0 Chlorotic 600 625 213Beets Roots 118 MG 90 120 90 9 Green 277

* Market Garden Plat.

The application of manganese salts was accompanied by an increasedyield as noted with previous crops (3) and also a decreased reserve of un-metabolized nitrogen as nitrate. The potassium reserve was likewise muchreduced in the greener plants of spinach grown on plat 21. The manganese-treated plants contained potassium to the extent of 768 parts per million,while those from the untreated area showed 1,213 parts per million in theplant solution.

140



GILBERT, MCLEAN AND ADAMS-MINERAL NUTRIENT CONTENT

Considering the nitrogen situation with spinach on plat 21, it must benoted that in reality there were two limiting fertilizer conditions operating,viz., insufficient manganese supply and a diminished nitrogen supply. Thisis seen when a comparison of yields of spinach is made between themanoanese-treated areas on plat 21 and plat 50 (near plat 21 and hadreceived nitrogen fertilization of 60 pounds per acre). Plat 21 was de-pressed 59 per cent. as compared to plat 50. This fact may help to accountfor the magnitude of the difference between the nitrate-nitrogen contentof the plant solution on the treated and untreated areas of plat 21. thelimiting iiitrogen supply having accentuated the condition.

When beets growing on plat 119 are considered, however, nitrogen havingbeen included in the fertilization, a comparison of yields between treatedareas of plat 119 and plat 118 (adjacent and fertilized with 90 pounds ofnitrogen per acre), shows the decrease of yield with decreased nitrogen to beonly 96 per cent. Hence nitrogen as a limiting factor was less active. Thenitrate-nitrogen difference between the treated and untreated beet plants isthus due more directly to the limiting manganese supply. The accumula-tion of nitrates both in the petioles and in the storage roots of beets withdeficient manganese supply, is fully as marked as in the leaves of spinach.Only at the end of the growing season, on October 8, did the nitrogen con-tent of the leaf petioles become equalized in the chlorotic, manganese-deficient plants and in the normal ones. This may be accounted for by thewithdrawal of nitrogen from the old leaves, as there was still a relativelyhigh nitrate content in the roots of the chlorotic plants on that date.

Insufficient nutrients as metabolic limiting conditionsThe most obvious conditions instrumental in limiting metabolism, are

insufficient supplies of raw materials. Under surroundings such as occurin nature these are usually considered to arise from deficiency in or un-availability of the supplies of nitrogen, phosphoric acid, and potassium, asfound in the soil in which the plant grows. When any one of these nutri-ents becomes limiting in supply, the limitation is reflected in the growthand may be measured by the yield at the end of the growth period. If, dueto some such limiting nutrient supply a difference in growth or yield results,other conditions being the same, some reflection may be expected in theamounts of this nutrient in the plant solution. It may also be profitableto examine the relationship of another nutrient to the limiting one, asshown by the plant solution content.

In table II some data are given which show clearly the reflection in theplant solution of the amounts of nitrogen and phosphoric acid applied infertilizer chemicals. An increase in either nutrient is shown in the currentamounts of nitrate-nitrogen and phosphate-phosphorus.

141



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The story as regards relative yields as measures of growth is, however,not so clear, and needs more explanation than is given in the table. Withall the crops tested the increase in phosphoric acid as supplied between plats55N and 65N is clearly shown both by the phosphate-phosphorus in the plantsolution and by the relative yields. But when we compare relative yieldsof tissue of plats 65N and 65S, the latter of which received 25 pounds extranitrogen per acre, we find that with turnips and carrots a decrease in yieldwas obtained in the case of 65S; with corn no difference resulted; while withcabbage there was an increase of 6 per cent. in the relative yields. If theparticular tissue examined be considered, this variation in yield will beunderstood. With turnips and carrots the root tissue was analyzed whilein the case of cabbage the leaves were used for analysis. The relative yieldsgiven in the table are of these tissues. If, however, the weights of turniptops from plats 65N and 65S be expressed as relative yields they are 81 and100 respectively. Thus the additional nitrogen fertilizer tended to produceleafy growth at the expense of the other portions of the plants. Nitrogenwas limiting for leafy growth only, and as the tissue examined in the caseof cabbage was leafy, this was reflected in the yield. With corn the stemtissue examined may be considered to have been intermediate and not likelyto be greatly affected by the extra nitrogen of 65S.

Considering next the effect of the supply of one nutrient upon the plantsolution content of another, we find that when the phosphoric acid appliedand the phosphate-phosphorus are low, the nitrate-nitrogen in the plantsolution is high and vice versa. This seems to hold with turnips, corn andcarrots, but not with cabbage. In this latter crop, however, the phosphate-phosphorus differences between the plant solutions of plats 55N and 65Nwere small and may not have been great enough to affect the nitrate-nitrogencontent. The reciprocal story is, however, not so clear. With the extranitrogen applied and the higher nitrate-nitrogen content of the solution inthe case of 65S, the phosphate-phosphorus was lower with turnips and cab-bage only. The story is confused with the other two crops. It would be ofinterest to observe the effect of a larger increase in nitrogen upon thephosphate-phosphorus content of the plant solution.

Changes in external conditions affecting metabolismFrom the foregoing facts it is evident that differences in the nutrient

level are reflected in the composition of the plant solution. There are alsotemporary changes in the concentrations of fertilizer elements in the plants.When such changes simultaneously affect the composition of the plants grow-ing under a variety of conditions of soil fertility, then we may expect to findthat they are due to some external condition. Therefore, a study was made

143



PLANT PHYSIOLOGY

p.p .m.N03- N

600

|~~~~~~~~~~~~~~~\ Celery400

ettuce200

Beet Tops

aept. Sept. ept. Oct. Oct.8 18 28 7 17

FIG. 1. Fluctuations in nitrate-nitrogen during decreasing temperature conditions.

of the weather conditions, and of the temperature and moisture content ofthe soil, to see if these factors could be correlated with changes in concen-trations of the plant solution.A conspicuous instance of this occurred about October 4 when the plant

solution concentrations were very low. In figs. 1, 2, and 3 are shown graph-ical representations of the nitrate-nitrogen, phosphate-phosphorus, andpotassium concentrations found at that time in celery, lettuce, and beet tops.The graph for each crop represents an average of determinations from two ormore plats where nutrient levels were not limiting. It will be noted thatwith the exception of phosphorus in beet tops the three nutrient elements de-crease in concentration through the month of September, and reach abouta minimal value around October 4 for all nutrient elements and crops. Amarked exception to this tendency for lowered concentration was noted inthe case of late spinach which was planted on August 27 and showed a highnitrogen content on September 27.

The diminishing concentration of the plant solution of the crops wasaccompanied by a decreasing amount of nitrate-nitrogen in the soil.*

Except where large amounts of nitrogen were added during the month,* Determinations by J. B. Smith, Assoc. Chemist.

144



GILBERT, AIMCLEAN AND ADAMS-MINERAL NUTRIENT CONTENT

TABLE IIINITRATE-NITROGEN CONTENT OF TIHE TOP 7 IN'C'HES OF SOIL UNDER GROWING CROPS (P. P. -A.)

CROP SPINACH BEETS CELERY

Plat No. 112 113 118 119 85 115 116 58 129 0

Aug. 31 ............ ..... ...... 13 10 8 12 4 25 10 13

Sept. 15 ..... ....... 61 2.(;...... ...... ...... ...... ...... ...... ...... ......

Sept. 27.44 22 8 4 6 28a 5 38a 10 iSa

Oct. 8.34 8 8 2 8 8 2 30 8 7

a Forty pounds of nitrogen per acre in nitrate of soda were added to each of theseplats on September 24, three days before sampling. This quite probably increased thenitrate content of the soil in these plats on September 27.

the nitrate content of the soil was low, or at least decreased, from August31 until October 8, under the crops of spinach, beets, and celery. Plat 112of spinach and plat 58 of celery were the only ones which retained a highnitrate content through the month of September.

P.p.m.K

6000 Celery

4000

Beet TOpW

2000

Sept. Sept. Sept. Oct. Oct.8 18 28 7 1L7

FIG. 2. Fluctuations in potassium during decreasing temperature collditions.

During the month of October the concentrations of the nutrient elementsgenerally increased in the plant solutions of the three crops (figs. 1, 2, and 3).

145



1PLANT PHYSIOLOGY

P.p.M.P04 r

3.

Beet Tops

| / __~~~~~/<~ Celery1 /,

Sept. Sept. Sept. Oct. Oct.8 18 28 7 17

FIG. 3. Fluctuations in phosphate-phosphorus during decreasing temperature conditions.

These were accompanied by a marked decrease in both soil and air tempera-tures, as shown in fig. 7. This fall in temperature may have contributed tothe accumulation of inorganic nitrogen, phosphorus, and potassium com-pounds in the plants, by depressing growth and decreasing the rate ofmetabolism.

The growth rates of the different crops studied were quite! uniformthroughout the period of most active growth, passing through a regulargrand period of growth for each crop (figs. 5 and 6). Changes in weatherand other changes of temporary character in the external conditions seemedto have little effect on the growth rate. The growth of every crop wasmarkedly depressed by deficiencies of N, P, and K on plats which were pur-posely kept deficient in these fertilizer elements.

The only noticeable depression in growth increments which may be at-tributed to temporary unfavorable conditions for growth was during theperiod from July 15 to July 29. This showed as a depression in the growthof cabbage leaves as measured on July 22 (fig. 5). The index of leaf areaused here in measuring the leaf growth of cabbage was the leaf product,obtained by multiplying the greatest width by the greatest length. Thisgave a value much larger than the actual leaf surface, but is believed to beapproximately proportional to the leaf area (4), (5), (6).

146



GILBERT, MCLEAN AND ADAMS-MINERAL NUTRIENT CONTENT. 147

There was a depression in height growth of turnips also, noted on July29. Height of turnips was measured from the ground surface to the tipof the tallest leaf.

These two depressions in growth were correlated with notably highvalues for the nitrate content of the plant solutions; of cabbage on July 29,and of turnips and carrots on August 6 (fig. 4). This depressed growth ofthe plants and attendant accumulation of nitrate in the plant solution wasaccompanied by and followed a period of hot weather extending from July15to25 (fig.7).

The moisture content of the soil was not critically low at any time duringthe summer. It fluctuated between 20 per cent. and 35 per cent. of thedry weight of the soil. The moisture-holding capacity of these soils by theHILGARD test was from 36 per cent. for the mineral soils to 44 per cent. forthe heavily-manured soils on the Market-Garden plats. Thus the calculatedwilting coefficient of the soil by the BiRios and SHANTZ formula (1) was

pap .ir.NO -N

800 t

600

400

200^Turnips

Cabbage

Carrots

July July Aug. Sept. 3ept.2 22 11 1 21

FIG. 4. Accumulation of nitrate-nitrogen during high temperature period, July 15-July 29.



PLANT PHYSIOLOGY

Plat 65l9

Plat 551

Plat 117

-1000 * * 0 \ Plat 119July July July July Aug. Aug.

7 15 22 28 4 11FIG. 5. Weekly growth increments of cabbage on well fertilized Experiment Station plats,

1926. Leaf product (length x width).

about 12 per cent., and the usually accepted optimum moisture content ofthe soil for plant growth-50 per cent. of the water-holding capacity-wasapproximately 18 per cent. to 22 per cent. So the moisture content of thesoil does not appear to have been at all critically deficient at any timeduring the growing season.

DiscussionThe current mineral content of the plant solution has been shown to be

an index of metabolic limiting conditions in three cases of inhibited

148




metabolism and these three cases have been discussed in turn. There nowremains the developing of a concept to embrace limiting conditions ingeneral. The authors have found it convenient to contrast the individualnutrient concentration in the plant solution with the level of water in thereservoir of a city supply system. This level is determined by the rate ofinflow and the demands made upon the system by water consumption. Inthe plant, the concentration of any one nutrient element is determined bythe available supply of that element in the soil and the permeability of plantmembranes to the nutrient element. These govern the rates of inflow. Atthe other end of the system, use of the individual nutrient element is deter-mined by the rates of metabolic processes, which are subject to changesthrough the action of limiting conditions. A further factor which may beexpected to affect the concentrations is the amount of moisture present inthe plant tissues. As this decreases with increasing saturation deficit, theplant solution may be expected to become proportionately more coneen-

15 lcm.

10

51

Plat 65N

Plat 55B

July July Aug. Aug. Aug. Aug.22 29 6 15 20 27

FIG. 6. Weekly growth increments of turnips on well fertilized Experiment Station plats,1926. Height of tallest leaf in cm.

149



PLANT PHYSIOLOGY

SOIL TEERATU E

AIR TDe~lURTURt ,.\

1K ^Seru

I I, .I i. .1 , * 1 1 ,J . . .. 1, 1!.Me la, 2Jun July sly July 0AU AOu Ag 2Aug. S epS psept Oct. Oct. Octis 22 2 1 222B I I1 21 31 0p 20 00 10 20 30

FIG. 7. Weather observations at Experiment Station plats during the growing seasonof 1926.

trated. The extent of this effect has not been determined as yet, but itmay be expected to be small except under severe conditions of evaporation,when it also would assume the role of a limiting condition and be reflectedin the current nutrient-element concentration.

SummaryIn this paper the current amounts of nitrate-nitrogen, phosphate-

phosphorus, and potassium are shown to have been correlated with arrestedmetabolism which was induced by the following limiting conditions:

1. A decreased supply of available manganese in a neutral soil, result-ing, in a marked chlorosis in beets and spinach.

2. Limiting amounts of phosphoric acid and nitrogen as supplied to thesoil in fertilizers.

3. Unfavorable weather and cultural conditions.RHODE ISLAND AGRICULTURAL EXPERIMENT STATION,

KINGSTON, R. I..

150



GILBERT, MCLEAN AND ADAMS-MINERAL NUTRIENT CONTENT 151

LITERATURE CITED

1. BRIGGS, L. J., and SHANTZ, H. L. The wilting coefficients for differentplants and its indirect determination. Bur. Plant Ind. Bull. 230:1-77. 1912.

2. GILBERT, B. E. The adaptation of certain calorimetric methods to theestimation of nitrates, phosphates and potassium in plant solu-tions. Plant Physiology 1: 191-199. 1926.

3. GILBERT, B. E., MlcLEAN, F. T., and HARDIN, L. J. The relation ofmanganese and iron to a lime-induced chlorosis. Soil Sci. 22: 437-446. 1926.

4. TIILDEBRANDT, F. AI. Leaf products as an index of growth in soy bean.Johns Hopkins Univ. Circ. March, pp. 202-205. 1917.

5. . A physiological study of the climatic conditions ofMaryland, as measured by plant growth. Physiol. Res. 2: 388-389. 1918.

6. _McLEAN, F. T. A preliminary study of climatic conditions in Mlaryland,as related to plant growth. Physiol. Res. 2: 141-142. 1914.



Documents

usually limiting the assimilation metabolism GILBERT · THE CURRENTMINERALNUTRIENT CONTENTOF THEPLANT SOLUTIONASANINDEXOFMETABOLIC LIMITING CONDITIONS* B. E. GILBERT, F. T. MCLEAN