Nutritional value of alfalfa using the interaction of irrigation, phosphate fertilizer, and arbuscular mycorrhizal fungi

Reasonable irrigation and fertilization can not only improve the yield and nutritional value of alfalfa, but also improve water and fertilizer use efficiency. To explore the effects of irrigation, phosphate fertilizer application, and arbuscular mycorrhizal (AM) fungi on the nutritional value of alfalfa (Medicago sativa), two irrigation treatments regulated deficit irrigation (RDI) and quota irrigation (QI); four fertility gradients 0 (P₀), 60 (P₁), 120 (P₂) and 180 kg·ha⁻¹ (P₃) phosphate fertilizer application; and two treatments AM (soil didn’t kill AM fungi) and −AM (soil killed AM fungi), were set up in this study. With the increase in phosphorus application rate, the crude protein content of alfalfa showed a trend of first increasing and then decreasing. The crude protein content and relative feeding value reached a maximum value in the P₂ treatment (120 kg·ha⁻¹), at 18.79% and 157.90%, respectively. The acid detergent fiber content and dry matter digestibility of the first crop alfalfa in the RDI treatment were higher than in the QI treatment. The crude protein content and relative feeding value of the third crop alfalfa in the QI treatment were markedly higher than those in RDI treatment, while the dry matter intake and neutral detergent fiber in the RDI treatment were markedly higher than those in the QI treatment. There was no significant difference in crude protein content, relative feeding value, dry matter digestibility, and acid detergent fiber content of alfalfa between the AM and −AM treatments, indicating that AM fungi in soil had no significant impact on the nutritional quality of alfalfa.