Cation‐Anion Balance of Field‐Grown Crops. II. Effect of P and K Fertilization and Soil pH¹

Abstract

Plant species differ in their cation‐anion balance, but the organic anion content (C‐A), excess‐base (EB), and EB/N ratio of a given plant species may vary considerably when grown under different environmental conditions. Nitrogen fertilizers, for example, increase the organic anion content of certain crop plants and alter their effect on soil acidity by reducing the EB/N ratio. The primary objective of this study was to determine the effect of a wide range in amounts of P and K fertilizers and of soil pH on the cation‐anion balance of several crop species grown under field conditions. Leaf and plant samples of corn (Zea mays L.) and plant samples of alfalfa (Medicago sativa L.) and oats (Avena sativa L.) were taken for analysis from plots of several field experiments that had received a wide range in amounts of P and K or of ground limestone. In general, phosphorus and potassium fertilizers decreased the C‐A and EB contents of corn leaves, oats, and alfalfa. The effect of P and K additions in reducing C‐A and EB seemed less where they had the least effect in increasing crop yields; and in some experiments, K additions had little or no effect on C‐A, EB, or yield. Limestone additions on two soils, resulting in pH changes from below 6.0 to above 7.6, increased C‐A and EB of corn leaves slightly in one experiment, but had no significant influence on C‐A, EB, or yield in the other. Potassium fertilizers lowered the EB/N ratio of corn leaves. However, K and P fertilizers and limestone additions resulted in only very slight changes in the EB/N ratio of corn, oats, and alfalfa plants; and no change in EB/N was observed in several of the comparisons. Thus, on the basis of their effect on the EB/N ratio of the crops harvested, P and K fertilizers and soil pH should not alter the plant effect on the base status of soils.

Growth ofPlantago lanceolata andPlantago major on a NO3/NH4 medium and the estimation of the utilization of nitrate and ammonium from ionic-balance aspects

“…7. The results show a very highly significant relationship (r = 0.997; Y = 0.950X + 0.043) and the points fall very close to the 1" 1 line, which infers the general validity of Equation (3) in calculating utilized NO 3 and/or NH 4 from pH shifts and ionic-balance data. Since results of many analyses and operational procedures are involved in the calculations, methodical errors account entirely for the observed deviations from the 1 : 1 line in Fig.…”

“…2 and 4). In P. major C-A is relatively constant and here a decreasing total cation level (particularly of K) is the most important phenomenon accompanying the decrease in NO 3 concentration (Figs. 3 and 4).…”

“…5) it can be concluded that the free NOa level in the plant material started to drop very sharply only when practically all the nitrogen had been taken up from the nutrient solution. In the ionic balance of P. lanceolata, this fall in NO 3 concentration is compensated for by decreasing C and increasing CI and C-A levels (Figs. 2 and 4).…”

“…The utilization of NOa and NH~ was estimated by subtracting free NO 3 and free NH4 from the total amounts of NO 3 and NH 4 taken up, and the values found were compared with the calculated NO 3 and NH 4 utilization using equation (3).…”

“…8, which clearly shows the depletion of free NO 3 and the increase of 'NO3-derived' organic N, as soon as all nitrogen has been taken up from the nutrient solution. After renewal of the NOJNH 4 nutrient solution (during the last week of the experiments) the reverse tendencies became operative again: an increase of free NO 3 and a relative increase of 'NH4-derived' organic N.…”