Effects of fertilization on hay yield and quality of alfalfa on the Loess Plateau

A 3-year field experiment was conducted to study the effects of nitrogen (N), phosphorus (P), and potassium (K) fertilizers applied on the hay yield and quality of alfalfa (Medicago sativa). The results showed that the hay yield of alfalfa was increased to varying degrees. According to the actual total hay yield over three years, hay yield was the highest, 39.76 t·ha^–1, with an increase of 44% compared to that of the control when N was 50 kg·ha^–1, P 120 kg·ha^–1, and K 60 kg·ha^–1. Based on the function relationship between 3-year hay yield and fertilization treatment, a maximum hay yield of 41.18 t·ha^–1 occurred when N was 68.3 kg·ha^–1, P 130.7 kg·ha^–1, and K 55.0 kg·ha^–1. The crude protein and relative feeding value were significantly increased (P < 0.05) and varied among three years, being the highest in the second year. The neutral detergent fiber and acid detergent fiber were significantly decreased (P < 0.05). There was no significant difference for crude ash among different fertilization treatments and years (P > 0.05).