Effect of Fertilizer N Rates on Soil N Uptake and Recovery of Applied N by Wheat in a Typic Haplustert

A micro-plot field experiment was conducted on a Typic Haplustert to study the contribution of soil and fertilizer N towards total N uptake by wheat using tracer methodology. The fertilizer N was added @ 40, 80 and 120 kg ha⁻¹ through urea tagged with ¹³N @ 3% atom excess. The grain yield and N uptake were increased by 89.1 per cent and 140.1 per cent, respectively, over control at the highest level of N application. The agronomic and physiological response of wheat to applied N varied between 10.3–15.8 and 24.6–34.5 kg grain kg⁻¹ N, respectively, and their highest values were recorded at 80 kg ha⁻¹ level. The A value of the soil did not alter with the fertilizer N rates, while soil N uptake was higher in fertilized plots than in the control plots and the highest soil N uptake (46.4 kg ha⁻¹) was recorded at the highest level of N application. Around 2/3^rd (38.5–40.2%) of the applied N was recovered by harvested crop. The proportion of the applied N remained in soil (24.6–34.0%) decreased and that lost from the soil (27.5–35.3%) increased with the increasing levels of applied N.