The grain yield and N uptake of maize response to increased plant density under reduced water and nitrogen supply

The development of modern agriculture requires the reduction of water and chemical N fertilizer inputs. Increased planting density can maintain higher yields, but also consumes more restrictive resources. However, it is unknown whether increased maize density could compensate the negative effects for reduced water and N supply on grain yield and N uptake in the arid irrigated areas. This study is a long-term positioning trial started in 2016. A split-split plot field experiment of maize was implemented with two irrigation levels: local conventional irrigation reduced by 20% (W1, 3240 m3 ha-1) and local conventional irrigation (W2, 4050 m3 ha-1), two levels of 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 density: local conventional density (D1, 75000 plants ha-1), increased density by 30% (D2, 97500 plants ha-1), and increased density by 60% (D3, 120000 plants ha-1) in the arid irrigated area of northwestern China in the 2020 to 2021. Our results showed that grain yield and aboveground N accumulation of maize were decreased under reduced water and N inputs, but increased maize density by 30% can compensate for the reduction of grain yield and aboveground N accumulation caused by reduced water and N supply of maize. When water was reduced while N application rate was unchanged, increased planting density by 30% enhanced grain yield by 13.9% and aboveground N accumulation by 15.3%. Under reduced water and N inputs, increased maize density by 30% enhanced N uptake efficiency and N partial factor productivity, as well as compensated for N harvest index and N metabolism related enzyme activity. Compared with W2N2D1, N uptake efficiency and N partial factor productivity were increased by 28.6 and 17.6% with W1N1D2. W1N2D2 was 8.4% of N uptake efficiency and 13.9% of N partial factor productivity higher than W2N2D1. W1N2D2 improved urease activity and nitrate reductase activity by 5.4% at R2 stage and 19.6% at V6 stage, increased net income and benefit: cost ratio by 22.1 and 16.7%. W1N1D2 and W1N2D2 decreased nitrate nitrogen and ammoniacal nitrogen contents at R6 stage in 40-100 cm, compared with W2N2D1. In summary, increased planting density by 30% can compensate the loss of grain yield and aboveground N accumulation under water and N inputs. Meanwhile, increased maize density by 30% improved grain yield and aboveground N accumulation when water was reduced by 20% while constant N application rate in arid irrigation areas.