Nitrogen application rates at rainfall gradients regulate water and nitrogen use efficiency in dryland winter wheat

Objectives We investigated the dynamics of water utilization and yield caused by various fertilizer rates under different rainfall patterns, to provide a scientific basis for precision fertilization in winter wheat on the Loess Plateau.

Methods A field experiment was conducted from 2017 to 2020 in Wenxi Experimental Demonstration Base of Shanxi Agricultural University, Shanxi Province, the planting system was summer fallow-winter wheat. The three experimental years were typically normal, dry, and wet years, respectively. N application levels at 0, 120, 150, 180, or 210 kg/hm² were set up (expressed as N0, N120, N150, N180 and N210, respectively). The N absorption, nitrogen and water utilization, yield, and yield components were investigated. The variation in these indices caused by two adjacent N rates was calculated in each year.

Results N180 significantly increased water consumption of wheat, regardless of precipitation distribution, and the largest variation of water utilization occurred from N 150 kg/hm² to 180 kg/hm² in wet and dry years, and from N 120 kg/hm² to 150 kg/hm²during the normal year. The highest wheat N accumulation from sowing to jointing stage, and the pre-anthesis export of N from leaf and spike + glume were recorded in N180 in wet year, and in N150 in the normal and dry years. The largest variation of export of pre-anthesis accumulated N and the accumulated N at maturity occurred from N 120 kg/hm² to 150 kg/hm², regardless of precipitation patterns. N180 exhibited the highest yield in wet year, which was 8.4%–35.6% higher than the other N rates; N150 elicited the highest yield in normal and dry years and was 8.9%–33.7% and 13.4%–48.9% higher than the other N rates, respectively. The largest variation of yield occurred from N 120 kg/hm² to 150 kg/hm², regardless of precipitation. However, the yield continued to increase significantly from N 120 kg/hm² to 150 kg/hm² in wet year, and the fertilizer efficiency peaked at 14.9 kg/kg at N150–N180 in wet year. While the yield increment from N 120 kg/hm² to 150 kg/hm² became negative in normal and dry year, N180 produced the highest water consumption, N absorption and utilization, and N recovery efficiency in the wet year, and N150 did in normal and dry years. Yield and water use efficiency of wheat were significantly correlated with the export of pre-anthesis accumulated N.

Conclusions In Conclusion, considering the effect of N application level and rainfall gradient, N180 increases water and N utilization, and N recovery efficiency in the wet year, and N150 in normal and dry years, which are the optimum N fertilization level for dryland winter wheat on the Loess Plateau.