Response of yield, yield components and water-nitrogen use efficiency of winter wheat to different drip fertigation regimes in Northwest China

Understanding the response of spike density (SD), grain number per spike (GN), and thousand kernel weight (TKW) to the application amount of nitrogen and irrigation, and clarifying the contribution of nitrogen and irrigation to the increased yield are vital for achieving high grain yield (GY), water and nitrogen use efficiency (WUE and NUE) in precision agriculture. A two-year (2018–2020) drip fertigated winter wheat experiment was conducted with three irrigation levels (rain-fed (RF), deficit irrigation (DI, 75% ETc) and full irrigation (FI, 100% ETc)) as main plot and four nitrogen levels (0 (NN), 85 (N3), 170 (N2) and 255 (N1) kg N hm⁻²) as subplot in Northwest China. The results showed that the tillers per plant (TP) significantly increased with increasing nitrogen application amount (0–255 kg hm⁻²), but the SD had insignificant difference between N1 and N2 levels due to lower effective spike rate (ESR) of N1. The GN firstly increased and then decreased with increasing nitrogen application amount. However, the TKW continued to decrease with increasing nitrogen application amount. Irrigation significantly increased SD and GN, but the impact on TKW showed uncertainty during two growing seasons. The structure equation model showed that both irrigation and nitrogen indirectly affect GY by affecting yield components, and nitrogen had the stronger influence to SD, GN and TKW than irrigation in this study. The highest GY (9.10 and 9.28 t hm⁻² in 2018–2019 and 2019–2020, respectively) was observed at DIN2, which increased by 200% and 277% in 2018–2019 and 2019–2020 growing seasons compared with RFNN treatment, respectively. And among these increased yield, more than 65% and approximately 20% were contributed by the application of nitrogen and irrigation, respectively. In addition, DIN2 also obtained the highest WUE and higher NUE due to lower actual evapotranspiration and nitrogen application amount. Therefore, deficit drip irrigation (75%ETc) coupled with 170 kg N hm⁻² was the best management strategy of irrigation and nitrogen under drip fertigation in Northwest China.