Effects of Different Moisture Conditions on Biological Nitrogen Fixation Capacity and Nutritive Value of Alfalfa (Medicago sativa L.) Seedlings

This research aimed to assess the impact of various moisture treatments on the nitrogen fixation and nutritive value of alfalfa seedlings. Potted alfalfa plants were served as the experimental material, and four moisture treatments were conducted (30%, 50%, 70%, and 90% of the field water capacity, labeled as W-30%, W-50%, W-70%, and W-90%). Evaluations of growth traits, physiological characteristics, nitrogen fixation capacity, and nutritive value of alfalfa were conducted in response to the different moisture treatments. Growth traits such as biomass of alfalfa were limited in both lower and higher water treatments compared to the W-70% treatment; Nitrogen fixation efficiency of alfalfa in W-70% treatment was increased by 190.19, 22.48 and 40.36% compared to W-30, 50 and 90% treatments, respectively, which was attributed to increased root activity and nitrogenase activity; The response of forage nutrient traits to moisture was similar to that of nitrogen fixation, with alfalfa in W-70% treatment having the highest crude protein and crude ash content and lowest crude fibre content; The ranking order of nutritive value under different moisture treatments was W-70% > W-50% > W-90% > W-30%. Moisture influenced nitrogen fixation by impacting alfalfa root activity and nodule nitrogenase activity. For alfalfa seedlings, a 70% field water capacity not only exhibited the highest nitrogen fixation efficiency but also displayed the superior nutritive value.