Abstract:

Chinese milk vetch （CMV） is the most important winter-grown green manure crop in the southern rice-cropping areas of China. This research investigated the appropriate ratio of phosphorus （P） to potassium （K） fertilizer during the cultivation of CMV， and the effect of rice straw （a substitute for K fertilizer） return to provide a basis for recommendations for efficient cultivation of CMV and reduction of chemical fertilizer use in Fujian paddy areas. A total of 12 treatments were established， including three phosphate fertilizer levels： 0， 15， 30 kg·ha^-1 （P₂O₅）， four potassium fertilizers levels： 0， 15， 30 kg·ha^-1 （K₂O） and 50% of rice straw from the preceding crop returned to the field. The agronomic characteristics， yield， nutrient content and nutrient capture of CMV were determined during the full-bloom period. It was found that， compared with no phosphate and potassium fertilizer （CK）， the largest increases in plant height， stem diameter， plant number， and total branch number were obtained with ratios of phosphate：potassium fertilizers of， respectively， 6.2%， 5.9%， 8.1%， 6.5%. The yields of fresh and dry CMV （compared to CK） were increased by 1.3%-12.8% and 1.4%-15.1%， respectively， and the highest dry matter yield of CMV occurred in a treatment that combined 30 kg·ha^-1 P fertilizer and 15 kg·ha^-1 K fertilizer. Nutrient captures of nitrogen， phosphorus and potassium were highest in a treatment which combined 30 kg·ha^-1 P and 30 kg·ha^-1 K fertilizer， and were higher than in the CK treatment by 19.2%， 18.8% and 25.9%， respectively （P<0.05 in each case）. The yield and nutrient capture of nitrogen， phosphorus and potassium in the treatment with 50% of rice straw returned to field were equivalent to those of the treatments with 15-30 kg·ha^-1 K fertilizer. In summary， appropriate combinations of P and K fertilizer application improved the growth of CMV， and resulted in higher herbage yield and nutrient capture， than in CK. Moreover， 50% return was able to largely substitute application of K fertilizer during the cultivation of CMV. Based on yield， nutrient capture， chemical fertilizer reduction and cost saving， the optimal combination was 15 kg·ha^-1 P and 15 kg·ha^-1 K fertilizer （or 50% rice straw return to the field in lieu of K fertilizer）.

Key words: Chinese milk vetch, phosphate fertilizer, potassium fertilizer, rice straw return, fresh green manure yield, nutrient capture