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FATE OF THE ¹⁵N-LABELLED UREA APPLIED TO IRRIGATED WHEAT GROWN AFTER COTTON HARVEST UNDER SEMIARID SUBTROPICAL CONDITIONS

TARIQ MAHMOOD, REHMAT ALI AND ZAHOOR ASLAM

Abstract: Fate of the fertilizer-N applied to irrigated wheat grown after cotton harvest was studied under field conditions using ¹⁵N-balance method. Of the total urea-N applied (100 kg ha^-1), 47.7 kg N ha^-1 was utilized by the wheat crop, the recovery being maximum in the grain component (30.0 kg N ha^-1), followed by straw (16.9 kg N ha^-1) and roots (0.9 kg N ha^-1. Of the 24.3 kg N ha^-1 of the fertilizer-N remaining in the soil at the crop harvest, most (22.2 kg N ha^-1 was present in the organic form, whereas maximum (15.6 kg N ha^-1 was recovered in the upper 10 cm soil layer. Total fertilizer-N loss during the wheat-growing season amounted to 28 kg N ha^-1, which was 1.5 times the denitrification loss directly measured from the same field.

Soil Biology Division, Nuclear Institute for Agriculture and Biology, P.O. Box 128, Faisalabad-38000, Pakistan.