Effects of Water-nitrogen Coupling on Water and Nitrogen Use Efficiencies and Yield of Sunflower at the North Foot of Yinshan Mountain

Objective The aims were to explore the influence of water and nitrogen (N) regulation on water and N utilization efficiency and grain yield of sunflower in the north foot of Yinshan Mountain, and to determine the reasonable water and N input of sunflower in this area.

Method Using a two-factor experimental design, three irrigation volumes were studied: W0 (rain feeding, no irrigation), W1 (watering irrigation, irrigation volume 1800 m³ hm⁻²), and W2 (over-irrigation, irrigation volume 3600 m³ hm⁻²⁾; three N applications were set at each irrigation volume, N0 (non-nitration), N1 (nitration is recommended, 135 kg hm⁻²), and N2 (2 times recommended, 270 kg hm⁻²). Using a conditional trial method, the effects of water-nitrogen coupling on sunflower grain yield, soil N content, water use efficiency, and N fertilizer absorption and utilization rates were studied, and the regression analysis was used to determine the optimal water and N application rates.

Result With the increase of irrigation and N application, sunflower grain yield, 100 - grain weight, water use efficiency and N fertilizer utilization rate showed a trend of increasing and then decreasing. The W1 and N1 treatments showed the highest grain yield and water and N utilization under different irrigation and N application conditions, respectively, which were significantly higher than those of the W0, W2, and N0, N2 treatments. At the same time, there was an extremely significant interaction effect between the irrigation and N application（P < 0.05）. The sunflower grain yield, water use efficiency and N fertilizer utilization rates in the W1N1 treatment were the highest at 3627.64 kg hm⁻², 8.88 kg hm⁻² mm⁻¹ and 65.13%, respectively, which were increased by 7.33%-193.11%, 10.37%-98.80% and 53.17%-393.78%, respectively, compared with the other treatments. Nitrate-N and ammonium-N accumulations in the 1 m soil layer were positively correlated with N application rates and negatively correlated with the amount of irrigation water, and both the amount of N applied and the amount of water irrigated (W) had highly significant effects on them.

Conclusion According to the nonlinear surface fitting, the optimal water and N combination of sunflower in the north foot of Yinshan was 2137.90 m³ hm⁻² and 174.10 kg hm⁻².