Effects of soil water and planting density on biomass allocation of alfalfa

This study was conducted to explore the response of biomass allocation to different soil moisture and plant density interactions, regulate plant biomass allocation through coupled management of plant density and soil moisture content in production management, improve water use efficiency and plant productivity, and improve the mechanism of plant adaptation to environmental factors. This study used alfalfa (Medicago sativa) as the study material. The effects of different soil moisture content 85%～90% (W₁), 75%～80% (W₂), 60%～65% (W₃), 35%～40% (W₄) and different plant densities 10 (D₁), 15 (D₂), 20 (D₃) plants per pot on the biomass allocation of alfalfa were analyzed through pot experiments. The results showed that soil moisture significantly affected the leaf biomass, stem biomass, aboveground biomass per plant, aboveground biomass, underground biomass, and root–shoot ratio of alfalfa (P < 0.05), with the decrease of soil moisture, all of them increased first and then decreased, and the peak value appeared when the soil moisture content was 75%～80% of the saturated water content; plant density significantly affected the aboveground biomass per plant, underground biomass, and root–shoot ratio of alfalfa (P < 0.05). With increased plant density, the aboveground biomass per plant increased first and then decreased, and when the plant density was 15 plants per pot, the underground biomass and root–shoot ratio increased. The interaction between soil moisture and plant density only significantly affected the aboveground biomass per plant (P < 0.05). When soil moisture was 75%～80% of the saturated soil moisture content and plant density was 15 plants per pot, the aboveground biomass per plant reached its maximum value of 5.00 g. This result indicates that alfalfa can adapt to soil moisture and plant density conditions by adjusting the distribution of aboveground and underground biomass to improve its water use efficiency and yield.