Original Articles

Soil and plant potassium optima for maize on a kaolinitic clay soil

Published in: South African Journal of Plant and Soil
Volume 9, issue 4, 1992 , pages: 193–200
DOI: 10.1080/02571862.1992.10634628
Author(s): M., P.W. Farina, Republic of South Africa, P. Channon, Republic of South Africa, G.R. Thibaud, Republic of South Africa, J.D. Phipson, Republic of South Africa


In South Africa, there is an extreme paucity of information relating maize (Zea mays L.) yields to soil and plant K levels and most K fertilizer recommendations are highly subjective. Controversy also surrounds the practice of relating K fertilizer recommendations to estimates of yield potential. The work reported here was conducted to address these shortcomings. The yield and plant compositional response of maize to a range of soil K levels was studied for eight seasons on a Metz clay soil (clayey, kaolinitic, thermic Plinthustalf). Relative yields were related to exchangeable soil K and the leaf parameters: K content, (Ca + Mg)/K and K DRIS index. Although grain yield maxima varied from 5.85 to 10.80 Mg ha−1, 91% of the relative yield variability was explainable in terms of exchangeable soil K. Leaf-based indices were also closely related to relative yield, but were sensitive to variations in topsoil moisture status prior to sampling and were not considered diagnostically superior to the K soil test. It is concluded that the optimum K level in this soil is c. 0.32 cmol L−1, that there is no justification for relating K requirement to estimates of yield potential and that leaf diagnostic criteria should be interpreted with circumspection.

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