Overwintering and Yield Responses of Two Late-Summer Seeded Alfalfa Cultivars to Phosphate Supply

Phosphorus (P) is one of the essential nutrients for alfalfa (Medicago sativa L.) growth, but P deficiency in soil is a common phenomenon. Applying an appropriate amount of P fertilizer for alfalfa in the establishment year improves winter survival, helps achieve sustainable high yields, and promotes the best economic returns. The objective of this study was to determine the effect of different P fertilization rates (0, 22, 44, and 66 kg P ha−1) on winter survival, forage yield, and root traits of two late-summer seeded alfalfa cultivars (dormant and semi-dormant) in the establishment and first production year. Our results showed that applying an appropriate amount of P fertilizer can increase forage yield and enhance the persistence of late-summer seeded alfalfa by promoting the development of crown and root traits and improving winter survival, especially for semi-dormant cultivars. Late-summer seeding and application of appropriate P fertilizer rates are effective agronomic methods for alfalfa in cold and arid winter regions, and can be used as strategies to improve fertility and stabilize soil from wind erosion for sustainable agriculture. To obtain high rate of survival in winter, the optimal P fertilization rates for the dormant and semi-dormant alfalfa cultivars in this study were 31.4 and 41.3 kg P ha−1, whereas the optimum P application rates for high forage yields were 31.3 and 31.5 kg P ha−1, respectively.