Management of rice straw with relay cropping of Chinese milk vetch improved double-rice cropping system production in southern China

Improved utilization of rice (Oryza sativa L.) straw and Chinese milk vetch Astragalus sinicus L., vetch) has positive effects on rice production. So far, few studies have investigated the productivity of vetch under different residue management practices in double-rice cropping system. The effects across seven years (2011–2017) of rice straw on growth and nutrient accumulation of vetch and the subsequent effects of rice straw and vetch on two succeeding rice crops in a vetch-rice-rice cropping system with establishment of vetch by relay cropping were examined. Treatments compared three practices for harvesting rice: use of low cutting height (low retained stubble) with either removal or retention of straw and high cutting height (high retained stubble) with retention of straw. Yields of the two rice crops after vetch were not affected by either thecutting height of stubble with retention of straw or by the management of straw (retention versus removal) with low cutting height of stubble. Yields of the two rice crops after vetch were significantly higher for high cutting height with retention of straw than for low cutting height with removal of straw, but the relative contributions of high cutting height and straw retention to the higher rice yield cannot be determined from this study. Higher cutting stubble with retention of straw can also increase yield stability of the double-rice grain as determined by a sustainable yield index. Significant increases in vetch biomassand nutrient uptake were observed in treatments fertilized during the rice season compared with unfertilized treatments. Improvements in the growing environment of the vetch by conserving soil water content, in plots by use of high cutting height (about 40 cm) with retention of straw were associated with the highest vetch biomass, nutrient uptake, and yield stability of vetch biomass. These increased nutrient inputs partially replaced the demand for chemical fertilizer and stimulated the rice yields. It can be concluded that retaining higher cutting stubble residues with retention of straw could be a better straw management practice for increasing the vetch biomass and nutrient use efficiency, thereby allowing utilization of high cutting height with retention of straw and vetch to improve the stability of rice productivity in a double-rice cropping system