Abstract

Attention is growing on the use of excessive nitrogen (N) and water in agricultural systems in Northwestern China because of lower water and N use efficiency. The soil NO₃⁻ dynamics and yield for cotton (Gossypium hirsutum L.) under the combined effects of drought and N additions, however, remain unclear. We investigated the effects of drought stress (367, 618, and 917 mm yr⁻¹) and N application levels (0, 150, 225, and 300 kg N ha⁻¹) on soil nitrate nitrogen (NO₃⁻) and yield in two years. Compared with optimum irrigation (917 mm), drought stress (618 and 367 mm yr⁻¹) significantly increased residual NO₃⁻ and decreased N loss. The 300 and 225 kg N ha⁻¹ treatment significantly increased NO₃⁻ content in most soil layers up to 200 cm depth, but N loss was also at a maximum with 300 kg N ha⁻¹. Applying 225 kg N ha⁻¹ with moderate drought stress (618 mm yr⁻¹) resulted in the highest cotton yields (2952 kg ha⁻¹⁾ and plant N uptake (148.7 kg ha⁻¹). Compared with the treatment of 150 kg N ha⁻¹ application with moderate drought stress (618 mm yr⁻¹), N agronomic use efficiency under the combination treatment of 225 kg N ha⁻¹ with moderate drought stress (618 mm yr⁻¹) had some decrease, but the difference was not significant. These results showed that reducing the N application rate to 225 kg N ha⁻¹ with moderate drought stress could be an optimum management practice for achieving high-yield, high-N use efficiency and could reduce soil N losses.