Effects of nitrogen application rates and irrigation regimes on grain yield and water use efficiency of maize under alternate partial root-zone irrigation

Faced with the scarcity of water resources and irrational fertilizer use, it is critical to supply plants with water and fertilizer in a coordinated pattern to improve yield with high water use efficiency（WUE）. One such method, alternate partial root-zone irrigation（APRI）, has been practiced worldwide, but there is limited information on the performance of different irrigation regimes and nitrogen（N） rates under APRI. The objectives of this study were to investigate the effects of varying irrigation regimes and N rates on shoot growth, grain yield and WUE of maize（Zea mays L.） grown under APRI in the Hexi Corridor area of Northwest China in 2014 and 2015. The three N rates were 100, 200 and 300 kg N ha–1, designated N1, N2 and N3, respectively. The three irrigation regimes of 45–50%, 60–65% and 75–80% field capacity（FC） throughout the maize growing season, designated W1, W2 and W3, respectively, were applied in combination with each N rate. The results showed that W2 and W3 significantly increased the plant height, stem diameter, crop growth rate, chlorophyll SPAD value, net photosynthetic rate（P_n）, biomass, grain yield, ears per ha, kernels per cob, 1 000-kernel weight, harvest index, evapotranspiration and leaf area index（LAI） compared to W1 at each N rate. The N2 and N3 treatments increased those parameters compared to N1 in each irrigation treatment. Increasing the N rate from the N2 to N3 resulted in increased biomass and grain yield under W3 while it had no impact on those under the W1 and W2 treatments. The W3 N3 and W2 N2 and W2 N3 treatments achieved the greatest and the second-greatest biomass and grain yield, respectively. Increasing the N rate significantly enhanced the maximum LAI（LAI at the silking stage） and P_n under W3, suggesting that the interaction of irrigation and fertilizer N management can effectively improve leaf growth and development, and consequently provide high biomass and grain yield of maize. The W2 N2, W2 N3 and W3 N3 treatments attained the greatest WUE among all the treatments. Thus, either 60–65% FC coupled with 200–300 kg N ha–1 or 75–80% FC coupled with 300 kg N ha–1 is proposed as a better pattern of irrigation and nitrogen application with positive regulative effects on grain yield and WUE of maize under APRI in the Hexi Corridor area of Northwest China and other regions with similar environments. These results can provide a basis for indepth understanding of the mechanisms of grain yield and WUE to supply levels of water and nitrogen.