Coordinated Soil-Plant Analysis I. Nutrient Cations

Analytical data for composite samples of soil and of corn leaf tissue collected during two years from four soil types, all soils receiving very closely similar fertility and management treatments, are presented. The area from which the samples were taken is operated as a seed production unit. The sequence of crops is cereal grain, corn, cereal grain, cereal grain, clover and timothy. Commercial fertilizer, 4-12-6, is used and crop residues are left on the land. Exchangeable calcium, magnesium and potassium, and exchange capacity were determined, and tests for free carbonates were made on the soil samples. Total calcium, magnesium and potassium values were determined for the leaf samples. All cation determinations were made by flame photometry. The range in exchangeable cation values for the four soils, except for the carbonate phase of one soil, was relatively small, about 30 percent, yet these soils under uniform management produced corn plants the leaf tissue of which differed significantly in content of potassium and of magnesium. The amounts of these elements in the leaf were modified strongly by the presence of free carbonate in the soil, and by seasonal and/or site influences. The exchangeable calcium: exchangeable potassium ratio in terms of milli-equivalents per 100 grams soil proved to be a much better index of the potassium content of the leaf than did the exchangeable potassium value alone, the latter expressed either as milli-equivalents or as percent saturation of the soil colloid. The calcium: potassium ratio showed a highly significant negative correlation with the amount of potassium in the leaf in both years. The exchangeable potassium of the soil showed a significant negative correlation with the magnesium content of the leaf in one year but not in the other. The potassium content of the leaf showed a significant negative correlation with the magnesium content of the leaf in both years. Further, this correlation was more significant than that of the potassium of the soil with the magnesium of the leaf in both years.