Cation-Anion Balance of Field-Grown Crops. II. Effect of P and K Fertilization and Soil pH

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 cansiderably 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.