Effect of potassium and magnesium application to soils on the dry-matter yield and cation composition of maize

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Abstract
SUMMARY: In a glasshouse experiment, fertilizer potassium and magnesium were applied in various amounts to 20 soils differing in the proportion of exchangeable potassium to the sum of the three exchangeable cations, potassium, calcium and magnesium. Maize, cv. Ganga-5, was grown as the test crop.In soils where the exchangeable cation ratio (K/Σ (K + Mg + Ca), in equivalents) was less than 0·025, potassium fertilizer significantly increased the dry-matter yield of maize. In soils where this ratio was between 0·026 and 0·05, application of potassium fertilizer was beneficial only up to the intermediate amount of 11 mg K/kg soil. Beyond this amount of application, addition of magnesium was necessary to increase yields. In soils where this ratio exceeded 0·05, potassium fertilizer reduced yields.An optimum ratio of exchangeable calcium, magnesium and potassium appears more important than their absolute amount. Magnesium application to high-potassium soils improved the cation equivalent ratio within the plant and the dry-matter yield.