Co-incorporation of high rice stubble and Chinese milk vetch improving soil fertility and yield of rice

Abstract: Rice straw return and green manure cultivation in winter fallow season are 2 effective ways of improving soil fertility in south China. Due to the relatively stable carbon to nitrogen ratio, either the rice straw return or green manure cultivation alone has its own limits in practice. Recently, the combined application of green manure and rice straw has been developed, while little is known about the impacts on crop yield and soil fertility. A field trial was conducted at an experimental station managed by National Engineering and Technology Research Center for Red Soil Improvement in Fengcheng, Jiangxi Province, China to explore effects of remaining high rice stubble, inter-planting green manure (Chinese milk vetch, Astragalus sinicus L.) and co-incorporation of rice straw and green manure on double rice and green manure yield and soil fertility. Field experiments were conducted in a rice-rice-winter fallow or rice-rice-Chinese milk vetch (MV) rotation system. A total of 5 treatments with different cultivation practices were included, (i) CK, rice-rice-winter fallow without rice straw return; (ii) RS, rice-rice-winter fallow with rice straw return; (iii) MV, rice-rice-MV without rice straw; (iv) MV+LRS, rice-rice-MV with return of low stubble (0 cm) of rice straw; (v) MV+HRS rice-rice-MV with return of high stubble (30 cm) of rice straw. The results showed that co-incorporation of RS and MV significantly increased fresh yield and nitrogen content of MV plants by 13.1% and 6.8% in MV+LRS and 32.2% and 5.2% in MV+HRS than those in MV alone, respectively. The average yield of double rice yield over the 4 years was significantly increased by 556.8 and 412.8 kg/hm2 in MV+HRS than in RS and MV, respectively. Compared to CK, the soil organic matter (SOM) content was significantly increased by 6.8% to 8.0% in RS and MV, the total nitrogen (TN) was marginally affected by the 2 treatments. Compared to CK, the soil inorganic N content was significantly decreased in treatments with RS and MV alone, while the available K was increased in RS. Different from soil inorganic nitrogen, manure treatments greatly improve available P content and the treatment of MV with HRS increased the available P by 18.0%. However, the treatments with rice straw could greatly increased soil available K by 8.0% (RS), 9.2%(MV+LRS) and 22.8%(MV+HRS), respectively. The soil microbial nitrogen were also significantly enhanced in the combinations than in MV or RS alone (P<0.05). The dissolved organic carbon and nitrogen were greater in the manure-rice straw combination treatments than CK. The treatments with rice straw enhanced the proportion of microbial biomass C in SOC and that of microbial biomass N in TN. Compared with the rice straw and manure alone, the co-incorporation of rice straw and manure increased the proportion of dissolved organic N in TN and inorganic N in TN. Collectively, the co- incorporation of rice straw and green manure could improve the rice yield and soil fertility in present conditions. The practice of keeping high stubble of rice straw standing in the field and returned together withgreen manure had the great promise to maintain and improve soil fertility and rice yield in south China.