Response of Water-Nitrogen Distribution and Use to Water Deficit under Different Applied Nitrogen Fertilizer Rates in Bromus inermis Grassland

Abstract

This study was about the water-nitrogen regulation model and its soil nutrient environment effect for increasing the yield and efficiency of Bromus inermis in the Hexi Corridor, Gansu Province, China. Bromus inermis was used as the research object in this study and four irrigation management types and four nitrogen application levels were set. The four irrigation management types (controlled by the percentage of field capacity (θf) at the jointing stage) were 75–85% (W0), 65–85% (W1), 55–85% (W2) and 45–85% (W3). The four nitrogen application levels were pure nitrogen 0 kg·ha−1 (N0), 60 kg·ha−1 (N1), 120 kg·ha−1 (N2) and 180 kg·ha−1 (N3). The effects of water-nitrogen regulation on the spatial and temporal distribution of soil moisture and nitrate nitrogen (NO3−–N), plant height, chlorophyll content, yield and water-nitrogen use efficiency of Bromus inermis were studied. Results demonstrated that (1) soil water content (SWC) was mainly affected by irrigation and W1 treatment helped maintain shallow soil (0–40 cm) water’s stability and avoided water redundancy or deficit in the 60–80 cm soil layer. The distribution of soil NO3−–N was mainly affected by nitrogen application. The N2 treatment could effectively increase the NO3−–N content in shallow soil (0–40 cm) and prevent nitrate-nitrogen leaching in the 60–100 cm soil layer. (2) Irrigation and nitrogen application could significantly increase the plant height and chlorophyll content of each cut of Bromus inermis. The average plant height and chlorophyll content of the N2W1 treatment were 66.99% and 30.30% higher than N0W3. (3) At the same time, irrigation and nitrogen application could significantly increase the yield of each cut of Bromus inermis, and the interaction between the two had a significant effect on the total yield. The total yield of the N2W1 treatment was the highest (12,259.54 kg·ha−1), 157.95% higher than N0W3. Irrigation and nitrogen application could significantly improve the water-nitrogen use efficiency of Bromus inermis, and their interaction only significantly impacted the partial-factor productivity of the applied nitrogen (PFPN). Meanwhile, the N2W2 treatment had the highest water use efficiency (WUE) (23.12 kg·m−3), and the N1W1 treatment had the highest PFPN (170.87 kg·kg−1). In summary, the moderate nitrogen application rate (120 kg·ha−1) combined with mild water deficit (65–85% θf at the jointing stage) could not only promote the high yield of Bromus inermis, but also avoid the leaching of water and nitrogen in deep soil. It is a suitable water and nitrogen management mode for Bromus inermis in the Hexi Corridor of Gansu Province, China.