Decomposition and nutrient release characteristics of four winter green manures in Hanzhong

To provide a theoretical basis for the scientific fertilization of rice under rice－green manure crop rotation systems in the Hanzhong area, dynamic changes in the decomposition and nutrient release characteristics of green manure crops were studied. An in-situ bag decomposition test was carried out for 145 days in the field, and the decomposition changes and nutrient release characteristics of four legume green manure crops (Astragalus sinicus, Vicia villosa, Lathyrus cicera, and Vicia sativa) were quantified. The results showed that the decomposition and nutrient release of the green fertilizers were fast in the early stage (0～14 d) and slow in the late stage (41～145 d). After 145 days, cumulative decomposition rates of milk vetch, hairy vetch, L. quinquenervius, and common vetch were 74.58%, 74.17%, 72.14%, and 72.57%, respectively. The average cumulative release rates of nitrogen (N), phosphorus (P), and potassium (K) were 85.64%, 75.23%, and 96.22%, respectively. After 145 days of decomposition of milk vetch, hairy vetch, L. quinquenervius, and common vetch equivalent to 22500 kg·ha⁻¹, the corresponding cumulative release amounts were 82.27, 134.73, 144.73, and 94.17 kg·ha⁻¹ for N, 14.68, 21.39, 21.21, and 17.25 kg·ha⁻¹ for P, and 70.90, 93.72, 85.23, and 82.13 kg·ha⁻¹ for K, respectively. In addition, the average cumulative N, P, and K release amounts of the four green manure crops were 113.99, 18.63, and 83.02 kg·ha⁻¹, respectively, indicating that the decomposition of green manure crops could provide 63.33% N, 20.70% P₂O₅, and 79.07% K₂O for the succeeding rice. Therefore, the four green manure crops, such as milk vetch, hairy vetch, L. quinquenervius, and common vetch, are suitable for planting as green manure crops in rice cropping system in Hanzhong area. The theoretical order of fertilizer reduction was hairy vetch ≈ L. quinquenervius > common vetch > milk vetch. Furthermore, Applying N and K fertilizer later due to the great potential of N and K reduction in the early stage of rice growth is recommended for manure decomposition.