Effects of nitrogen application rate on annual yield and N-use efficiency of winter wheat-summer maize rotation under drip irrigation

Objectives Fertigation is a water and fertilizer efficient technology in crop production. We studied the suitable N application rate in winter wheat-summer maize production in North China Plain to achieve high N fertilizer efficiency and low soil N loss.

Methods The fertigation experiment in the winter wheat/summer maize system was carried out in Jiaozhou Modern Agricultural Demonstration Park, Qingdao Agricultural University, from 2018 to 2020. The nitrogen fertilization treatment levels for wheat/maize were no N input (N0), 150/150 kg/hm² (N1), 210/225 kg/hm² (N2), and 270/300 kg/hm² (N3), taking the N 240/240 kg/hm² under conventional irrigation method as the control (CK). The crop yield, N use efficiency, and soil N residue were analyzed.

Results The winter wheat and summer maize yields in N2 and N3 were higher than in other treatments (P<0.05). The dry matter and N accumulation of winter wheat and summer maize in N2 and N3 were higher than in N1 and CK (P<0.05). The N partial factor productivity (NPFP) of winter wheat and summer maize decreased with increasing N levels. N use efficiency declined in the winter wheat season with increasing N levels. In the summer maize season, N use efficiency in N2, N1 and N0 treatments were similar and higher than N3 and CK (P<0.05). The N agronomic efficiency of winter wheat and summer maize decreased with increasing N levels. The highest N use efficiency and N agronomic efficiency were recorded in N2. With the increasing of N levels, the total N and nitrate N content in the 0–100 cm soil layer showed a rising trend. The total N accumulation was mainly concentrated in the 0–40 cm soil layer. The difference in soil total N content between N3, N2, CK and N0, N1 in 0–100 cm soil layer increased as the rotation year advanced. Compared with N3 and CK, N2 effectively inhibited the accumulation of nitrate N in the surface soil layer and its migration to the deeper soil layer, reducing the risk of nitrate leaching.

Conclusions Applying N 210 and 225 kg/hm² in winter wheat and summer maize (N2) recorded the highest crop yield and biomass, relatively high N use efficiency, and reduced nitrate N migration to the deeper soil layer. Thus, adopting the N2 application rate for wheat and maize is appropriate in the North China Plain under drip fertigation.