INFLUENCE OF TOP-DRESSED NITROGEN IN ALLEVIATING ADVERSE-EFFECTS OF FLOODING ON GROWTH AND YIELD OF WHEAT IN A SODIC SOIL

Saturated and/or temporary flooding conditions following irrigation or rains during the growing season of wheat (Triticum aestivum L.) is common in sodic soils in the Indo-Gangetic alluvial plains of India. Nitrogen deficiency triggered by saturation is considered to be an important cause of low yields. This study evaluated the use of increased rate of top-dressed urea-N in alleviating the adverse effects of flooding imposed at the time of the first irrigation in a sodic soil (pH 9.2, exchangeable sodium 32%). In a control treatment (T-1), excess water was drained 12 h after the first irrigation, while in remaining treatments (T-2 to T-5), it was allowed to stand for 4 days following the first irrigation. All treatments received a basal dose of 40 kg N ha(-1) as urea. Treatments T, and T, received 80 kg N ha(-1). Treatments T-3, T-4 and T-5 had 100, 120 and 140 kg N ha(-1), respectively, applied in two splits, after the first and a second irrigation. Results showed that increasing the rate of top-dressed urea-N from 80 to 100, 120 and 140 kg ha(-1) in undrained plots significantly increased the grain and straw yields, root and shoot dry weights, plant height, tiller numbers, spikelet numbers per spike, spike length, N uptake and apparent N recovery. Supplementing N also promoted uptake of P, K and Zn, the effects being more pronounced in 60-day-old plants. Uptake of Na was considerably reduced, while that of Fe and Mn remained unaffected. Results suggest that increasing the rate of top-dressed urea-N helps alleviate the adverse effects of flooding on wheat.