COMPARISON OF SINGLE LARGE BROADCAST AND SMALL ANNUAL SEED-PLACED PHOSPHORUS TREATMENTS ON YIELD AND PHOSPHORUS AND ZINC CONTENTS OF WHEAT ON CHERNOZEMIC SOILS

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Abstract
Yield and P and Zn contents of wheat from plots on a Dark Brown Chernozemic clay soil which received single broadcast P applications and annual seed-placed P applications were compared in a 6-yr study. Broadcast P applications of 20, 40, 80 and 160 kg P ha−1 increased the average yield by 9, 24, 33 and 35%, respectively. Yearly seed-placed P treatments of 2.5, 5, 10 and 20 kg P ha−1 applied over the first 5 yr of the study increased the average yield by 10, 15, 24 and 29%, respectively. The broadcast application of 40 kg P ha−1 increased yields over 5 yr and had an average yield and P uptake similar to that of the annual seed-placed applications of 10 and 20 kg P ha−1. Broadcasting 80 and 160 kg P ha−1 increased yields over 6 yr. Soil levels of extractable NaHCO3-Pi indicated future increases may occur. Yields from plots receiving consecutive seed-placed P treatments significantly benefited from the P residues of previous seed-placed applications. Plant zinc concentration was significantly reduced by the broadcast application of 160 kg P ha−1 and the seed-placed application of 20 kg P ha−1. Key words: Broadcast P, seed-placed P, residual P, P-Zn interaction