| According to the 18-year fertilizer experiment, the paper discusses and analyzes the dynamic changes in alfalfa at different growth stages with different farming modes. The results showed that the N contents of alfalfa under different fertilizations did not significantly differ, but the P content obviously increased; the use of only P fertilizers could not significantly change the N content in alfalfa. In alfalfa rotation, the N contents of alfalfa with different growing lengths tended to decline while in the aboveground part of alfalfa, the P and K contents varied in different patterns and the K content increased as alfalfa grew longer and longer. |