Abstract: The overall aim of our research is to improve the microenvironment ecological factors of alfalfa and to recommend appropriate regulation of water and fertilizer use based on scientific evidence. In this study, the relationship between the amounts of inputs (irrigation and nitrogen fertilizer) and the growth and microclimate characteristics of alfalfa were investigated in a 2-year drip-irrigation field experiment in the Yellow River irrigation region of Ningxia. The results showed that the amounts of drip irrigation and nitrogen fertilizer significantly affected the plant height, leaf area, and yield of alfalfa. Compared with the no-fertilizer treatment, fertilization decreased the air temperature, soil temperature, and illumination within the alfalfa stand, but increased the relative humidity. The microenvironment of alfalfa varied among the different irrigation treatments. As the amount of irrigation increased, the relative humidity in the alfalfa stand gradually increased, and the cooling effects on air temperature and soil temperature became stronger. There were strong positive correlations between plant height and leaf area, grass biomass, and relative humidity. There were significant negative correlations between plant height and illumination, temperature, and soil temperature. Therefore, a reasonable decrease in the amount of irrigation and nitrogen fertilizer can not only maintain good growth of alfalfa, but also increase grass yield and improve grassland ecological conditions.

Key words: alfalfa, water and nitrogen supply, grass biomass, microclimate