Effects of light and water on alfalfa growth and water use

Water affects forage growth and production, and light energy drives forage water use and production of aboveground biomass, all of which are important factors limiting the development of livestock farming on the Loess Plateau. In this study, we combined the characteristics of long light hours and water shortage on the Loess Plateau to elucidate the effects of water and light intensity on the growth of alfalfa (Medicago sativa) to provide a basis for optimizing the planting pattern and cultivation management of alfalfa. We used pot experiments to study two water supply levels (high water: 70%～100% of field water holding capacity, low water: 50%～70% of field water holding capacity) and two light intensities (high light: total radiation received = approximately 20.7 MJ·(m²·d)⁻¹, equivalent to solar radiation on a sunny day, and low light: total radiation received = approximately 14.8 MJ·(m²·d)⁻¹, equivalent to solar radiation on a semi-shady or semi-cloudy day), to elucidate the effects of light intensity and water on the growth dynamics, aboveground biomass, and water use of alfalfa. The results showed that the number of leaves, leaf area, and aboveground biomass of alfalfa were the highest (15.97 g·plant⁻¹) under high water and low light treatments. Under both light intensities, aboveground biomass, water consumption, and water use efficiency increased by 158.1%, 68.8%, and 65.5% on average, respectively, in alfalfa in the high water treatment compared with the low water treatment. Under both water conditions, aboveground biomass, water consumption, and water use efficiency increased by 89.8%, decreased by 9.5%, and increased by 60.0% on average, respectively, under low light treatment compared with the high light treatment. Therefore, reducing light intensity could improve aboveground biomass and water use efficiency of alfalfa.