Nutrient release characteristics of leguminous green manures in yellow soil uplands

To provide a scientific basis for the scientific returning of leguminous green manure and reasonable reduction of chemical fertilizer application in yellow soil uplands, a nylon bag net bag embedding method was utilized for the decomposition and nutrient release of leguminous green manure with different water contents and biochar addition in the yellow soil uplands experimental base of the Guizhou Academy of Agricultural Sciences. The trend of the decomposition rate was the same between the different treatments, which showed that the decomposition rate was fast at first, then slowly decomposed, and finally the decomposition stabilized and reached equilibrium. The total decomposition rate was air dried green manure + biochar > fresh green manure + biochar > air dried green manure > fresh green manure. After 180 days of decomposition, the decomposition rates of fresh green manure, air dried green manure, fresh green manure + biochar, and air dried green manure + biochar were 74.77%, 83.13%, 92.69%, and 95.83%, respectively. The decomposition rate of green manure treated with biochar was higher than that without biochar, and the decomposition rate of air dried green manure was higher than that of green manure. Similar to the decomposition rate, the decomposition rates of N and P were fast at first, then slowly decomposed, and finally the decomposition stopped and reached equilibrium. After 180 days of decomposition, the decomposition rates of N and P for fresh green manure, air dried green manure, fresh green manure + biochar, and air dried green manure + biochar were 73.55%, 83.80%, 92.00%, 95.00%, and 76.40%, 87.13%, 93.31%, 96.27%, respectively. The decomposition rate of K was higher than that of N and P, the release rate of green manure in different treatments reached more than 80% after 30 days of decomposition. The decomposition rate of the air dried green manure was higher than that of the fresh green manure, and adding biochar improved the decomposition rate of air dried and fresh green manure. In actual operation, the decomposition rate of green manure with different water content was different; leguminous green manure can be returned to the field after air drying, and biochar and other alkaline substances are added to improve the decomposition efficiency. It was indicated that after returning green manure to the field, the application rates of N and K fertilizer should be decreased and K fertilizer could be used in crop growth at a later stage, while N and P should be maintained as a usual practice at the early crop growth stage.