Abstract: Irrigation and nitrogen management are perhaps the most important aspects for grain production in the arid oasis agricultural area of Northwest China. A field experiment was conducted on sandy farmland to determine the effects of different irrigation amounts (conventional irrigation, 12 000 mm ha^-1; 10% water-saving irrigation, 10 800 mm ha^-1; 20% water-saving irrigation, 9 600 mm ha^-1) and nitrogen rate (0, 150, 225, 300, and 375 kg ha^-1) on maize yield in the marginal oasis in the middle of Heihe River Basin. Also, nitrogen use efficiency (NUE), irrigation water productivity (WP) and N accumulation in 0–200 cm soil layer were discussed. There were no significant differences in maize yield and aboveground biomass among different irrigation treatments. Combining nitrogen fertilizer with manure, phosphate and potassium fertilizers, N application with 150–375 kg N ha^-1 increased maize yield by 74.8%–108.6% compared with no N applied. However, maize yield did not increase significantly at N rate above 225 kg N ha^-1. NUE ranged from 50.6% to 83.7% and decreased with increasing N application rate, with a strong decrease at N rate above 225 kg N ha^-1. Under the treatment of N fertilizer application, WP ranged from 0.97 to 1.35 kg m^-3 and decreased with increasing irrigation amount. WP did not increase significantly when N rate was above 225 kg N ha^-1. There was significant coupling effect between irrigation and nitrogen application. The treatments with conventional irrigation and high nitrogen rates had maximum yield, however, the water and nitrogen use efficiencies decreased significantly. There were no evident differences in water content in the 0–160 cm soil layer measured before each irrigation among the three irrigation treatments, indicating that conventional irrigation treatment can not conserve soil water for a longer period to used in maize growth compared to water-saving irrigation treatment. In conventional irrigation treatment, NO₃^－-N accumulation in the 0–200 cm soil layer was lower than that in the two water-saving irrigation treatments, indicating that more amount of NO₃^－-N was leached to deeper soil layers which increase the risk of N contamination to groundwater.
Based on the comprehensive consideration for high effective use of water and nitrogen, mitigation of water resource shortage and its sustainable use and decrease of the pollution risk of water by N, rational regulation and control of irrigation and fertilization and reducing moderately the inputs of irrigation water and nitrogen fertilizer should be a reasonable alteration for sandy farmland management and expectant water-saving potential can be achieved.

Key words: Irrigation amount, Nitrogen rate, Maize, Yield, Water and nitrogen use efficiency, Sandy farmland