Abstract

The development of modern agriculture requires the reduction of water and chemical N fertilizer inputs.  Increasing the planting density can maintain higher yields, but also consumes more of these restrictive  resources. However, whether an increased maize density can compensate for the negative effects of  reduced water and N supply on grain yield and N uptake in the arid irrigated areas remains unknown. This  study is part of a long-term positioning trial that started in 2016. A split-split plot field experiment of maize  was implemented in the arid irrigated area of northwestern China in 2020 to 2021. The treatments included  two irrigation levels: local conventional irrigation reduced by 20% (W1, 3,240 m3 ha–1) and local conventional  irrigation (W2, 4,050 m3 ha–1); two N application rates: local conventional N reduced by 25% (N1, 270 kg  ha–1) and local conventional N (360 kg ha–1); and three planting densities: local conventional density (D1,  75,000 plants ha–1), density increased by 30% (D2, 97,500 plants ha–1), and density increased by 60% (D3,120,000 plants ha–1). Our results showed that the grain yield and aboveground N accumulation of maize were lower  under the reduced water and N inputs, but increasing the maize density by 30% can compensate for the reductions of  grain yield and aboveground N accumulation caused by the reduced water and N supply. When water was reduced  while the N application rate remained unchanged, increasing the planting density by 30% enhanced grain yield by  13.9% and aboveground N accumulation by 15.3%. Under reduced water and N inputs, increasing the maize density  by 30% enhanced N uptake efficiency and N partial factor productivity, and it also compensated for the N harvest  index and N metabolic related enzyme activities. Compared with W2N2D1, the N uptake efficiency and N partial factor productivity increased by 28.6 and 17.6% under W1N1D2. W1N2D2 had 8.4% higher N uptake efficiency and 13.9%  higher N partial factor productivity than W2N2D1. W1N2D2 improved urease activity and nitrate reductase activity  by 5.4% at the R2 (blister) stage and 19.6% at the V6 (6th leaf) stage, and increased net income and the benefit:cost  ratio by 22.1 and 16.7%, respectively. W1N1D2 and W1N2D2 reduced the nitrate nitrogen and ammoniacal nitrogen contents at the R6 stage in the 40–100 cm soil layer, compared with W2N2D1. In summary, increasing the planting  density by 30% can compensate for the loss of grain yield and aboveground N accumulation under reduced water and  N inputs. Meanwhile, increasing the maize density by 30% improved grain yield and aboveground N accumulation  when water was reduced by 20% while the N application rate remained constant in arid irrigation areas.