Effects of Water Saving and Nitrogen Reduction on Lodging Resistance and Grain Yield of Spring Wheat in the Yellow River Irrigation Area of Ningxia

The study on the effect of nitrogen reduction and water saving on the stem strength and grain quality of spring wheat aims to provide theoretical basis for the sustained and stable yield increase of spring wheat, efficient utilization of irrigate and nitrogen, and improvement of spring wheat’s lodging resistance in Yellow River Irrigation Area of Ningxia.

Using Ningchun No.4 as test material, in 2021 and 2022, split-zone field experiment was conducted to investigate the effects of irrigation treatments (conventional irrigation (400 mm, WC), 20% water saving (320 mm, W1), and 40% water saving (240 mm, W2) and nitrogen application treatments (conventional nitrogen application (270 kg·hm^-2, NC), 25% nitrogen reduction (202.5 kg·hm^-2, NJ), and no nitrogen application, N0) on stem strength, yield and grain quality of spring wheat.

The 25% N reduction and 20% water savings did not significantly reduce spring wheat plant height, stem diameter, or accumulation of aboveground biomass compared to conventional N application. There was no significant difference in stem strength and stem potassium content of spring wheat treated with reduced and conventional nitrogen application levels, but on the basis of reduced nitrogen, stem strength and stem potassium content of spring wheat treated with 20% water saving was significantly higher than that of conventional irrigation treatment. At the filling stage, stem strength increased by 14.9% and 16.3%, and stem potassium content increased by 13.4% and 11.9% in the water-saving 20% treatment compared to the conventional flooding treatment in both years at the reduced nitrogen level, while at the maturity stage, stem strength increased by 19.0% and 8.3%, and stem potassium content increased by 10.5% and 9.0%, respectively. Stem strength of spring wheat showed a decreasing trend as the reproductive process progressed. Correlation analysis showed that stem strength was highly significantly positively correlated with plant height and above-ground biomass, significantly positively correlated with stem potassium content, and not significantly correlated with stem diameter. Among the water-nitrogen treatments, the spring wheat yield was highest in the 20% nitrogen reduction and water conservation treatment, amounting to 8 092 and 5 516 kg·hm^-2 in 2021 and 2022, respectively. At the same nitrogen application, the soluble sugar and protein contents of spring wheat grain showed an increasing and then decreasing trend with the decrease of irrigation quota, and the 25% nitrogen reduction and 20% water saving treatment reached the maximum value, which increased by 14.4%, 16.7%, and 25.5%, 23.5%, respectively, compared with the conventional water and nitrogen treatments, while there was no significant difference in starch content among the irrigation and nitrogen treatments. It was further found that stem strength was highly significantly and positively correlated with yield and protein content in grain and not significantly correlated with starch and soluble sugar content in grain.

Water saving of 20% under nitrogen reduction promoted the growth of spring wheat plant height and stem diameter, increased the accumulation of aboveground biomass, and increased the potassium content of stems, which in turn improved the stem strength of spring wheat, reduced the risk of lodging, increased the yield of spring wheat and improved the grain quality. Therefore, it was concluded that 20% water saving under nitrogen reduction conditions is a suitable irrigate and nitrogen management model for spring wheat in the Yellow River Irrigation Area of Ningxia.