Abstract: This research investigated the effects of water and fertilizer and their interaction on the yield, hay quality and seed yield of Leymus chinensis in the Ningxia irrigation area. The L. chinensis cultivar used was Zhongke No.2. A two factor split-plot experiment design was adopted, with water as the main plot treatment and fertilizer as the sub-plot treatment. A quadratic polynomial stepwise regression and normalization was used to identify the combination of irrigation and fertilizer that best optimized the multi-factor benefit. It was found that irrigation had significant effects on seed and hay yield, fertilizer partial productivity (PFP), irrigation water use efficiency (iWUE), and hay quality (P<0.05). Fertilization had significant effects on seed and hay yield, PFP, quality, and hay iWUE (P<0.05); significant (P<0.05) water fertilizer interactions were observed for thousand-grain weight, heading rate, hay quality, hay PFP and iWUE. The seed yield was highest with 360 mm irrigation and 132 kg·ha^-1 fertilizer application. The hay yield and relative feeding value (RFV) were highest with 360 mm irrigation and 540 kg·ha^-1 fertilizer application. Stepwise analysis showed that the interaction effect of water and fertilizer differs depending on the purpose of L. chinensis cultivation. When L. chinensis is planted for hay production and forage quality is important, the recommendation is to apply 288-360 mm and 324-540 kg·ha^-1 of fertilizer; when L. chinensis is planted for seed production and when efficient use of fertilizer is important, the recommendation is to apply 288-360 mm irrigation and 108-216 kg·ha^-1 of fertilizer.

Key words: Leymus chinensis, coupling of water and fertilizer, hay yield, seed yield, nutritional value