Variation characteristics of nutrient contents in a 5-year Medicago sativa and Poa pratensis rotation

Alfalfa crop rotation is a high-level planting method that is beneficial for the balanced use of soil nutrients and the prevention of diseases, insects and grass damage. In this paper, we investigated the variation of soil nutrients in a 5-year Medicago sativa ‘Gannong No.9’ →Poa pratensis ‘Haibo’ rotation, with continuous cropping of alfalfa used as control. Samples we collected at a soil depth of 0 – 20 cm and 20 – 40 cm soil every three months, as well as in April, July and October in the 1 – 2 years after crop rotation. Organic matter, total nitrogen, available nitrogen, total phosphorus and total potassium content was measured. The results showed that the content of soil organic matter, total nitrogen, available nitrogen, total phosphorus and total potassium in the first year after rotation was higher than that in the second year. In the first year after rotation, the nutrition indices of soil organic matter, total nitrogen, available nitrogen, total phosphorus and total potassium increased by16.32%、6.16%、4.13%、17.94% and 8.29%, respectively, in the 0 – 20 cm layer, and increased by 30.69%、5.00%、2.29%、3.33% and 30.00%, respectively, in the 20 – 40 cm soil layer . In the second year after rotation, these nutrition indices increased by 9.45%, 5.14%, 3.54%, 24.49% and 19.37%, respectively, in the 0 – 20 cm layer, and increased by 16.70%、0.97%、4.89%、25.00% and 26.48%, respectively, in the 20 – 40 cm soil layer. The content of soil organic matter, total phosphorus and total potassium in alfalfa to Poa pratensis rotation was significantly higher than that of continuous alfalfacropping, while the content of total nitrogen and available nitrogen in rotation soil had little difference with that of continuous cropping. In summary, alfalfa-Poa pratensis rotation improves organic matter, total phosphorus and total potassium content, and the utilization of nitrogen.