早稻秸秆还田和减钾对晚稻产量和土壤肥力的影响

水稻秸秆是华南双季稻区重要的有机肥资源，为探讨早稻秸秆还田条件下钾肥减量施用对晚稻产量和土壤肥力的影响，于广东省白云区和惠阳区开展大田试验，设置常规施肥（CK）、秸秆还田+常规施肥处理（RS）和秸秆还田+钾肥减施20%（RS-K）这3个处理，分析不同处理的晚稻生物量、钾含量和产量，及土壤速效钾、有机碳、细菌多样性和群落结构等土壤肥力性质的变化.结果表明，RS-K处理的水稻生物量和产量与CK处理无显著差异.与CK相比，RS处理的水稻植株钾含量平均提高了3.97%（白云）和6.91%（惠阳）.RS-K处理的植株钾含量在水稻生长前期显著低于CK处理，但在水稻生长后期两者无显著差异.与CK相比，RS处理显著提高了土壤速效钾含量，平均增幅达13.90%（白云）和21.67%（惠阳）；RS-K处理的土壤速效钾也较CK处理提高了3.56%（白云）和4.23%（惠阳）.秸秆还田处理显著提高了土壤可溶性有机碳含量，但对土壤pH值、有机碳、微生物量碳、硝态氮、铵态氮和有效磷含量无显著影响.与CK相比，秸秆还田处理显著提高了土壤细菌的Chao1和Shannon指数；秸秆还田处理还显著提升了变形菌门、放线菌门和硝化螺旋菌门的相对丰度，而降低了酸杆菌门、拟杆菌门和厚壁菌门的相对丰度；冗余分析表明，土壤有机碳、可溶性有机碳、微生物量碳、有效磷和速效钾含量是驱动土壤细菌结构群落变化的主要环境因素.综上，早稻秸秆还田可提高土壤速效钾含量和晚稻钾含量，在早稻秸秆还田条件下钾肥减施20%对晚稻钾营养水平和产量均没有产生明显负面影响，且能提高土壤有机碳和细菌多样性.因此，在华南双季稻区，早稻秸秆还田配合钾肥减施20%有利于化肥减施、粮食稳产和培肥地力，对农业绿色发展具有重要意义.

Effects of Early Rice Straw Returning with Reducing Potassium Fertilizer on Late Rice Yield and Soil Fertility

Rice straw is an important organic fertilizer in the region for double-cropping rice in South China. To reveal the effects of early rice returning with reducing potassium fertilizer on the yield of late rice and soil fertility, field experiments were carried out in Baiyun and Huiyang district in Guangdong province. The biomass, K content, and yield of late rice and the soil fertility properties, such as soil available potassium, soil organic carbon, bacterial diversity, and bacterial community structure were analyzed under three treatments (CK, conventional fertilization; RS, straw returning with conventional fertilization; RS-K, straw returning with reducing 20% potassium fertilizer). The results showed no significant differences in the biomass and yield of late rice between the RS-K treatment and CK treatment. Compared with that in CK, the RS treatment significantly increased the K contents of rice by 3.97% (Baiyun) and 6.91% (Huiyang). The K contents of late rice under the RS-K treatment were significantly lower than that under the CK treatment during the early growth period in rice, but there was no significant difference between them during the late growth period. Compared with that in CK, the soil available K in the RS treatment increased by 13.90% (Baiyun) and 21.67% (Huiyang) (P<0.05), and the soil available K in the RS-K treatment also increased by 3.56% (Baiyun) and 4.23% (Huiyang). Compared with that in the CK treatment, the soil dissolved organic carbon increased significantly in the RS and RS-K treatments (P<0.05). Compared with that in CK, the straw returning treatments (RS and RS-K) significantly improved the Chao1 and Shannon indexes of soil bacteria (P<0.05). Straw returning treatments (RS and RS-K) increased the relative abundance of Proteobacteria, Actinobacteria, and Nitrospirae compared with that in CK, whereas they decreased the relative abundance of Acidobacteria, Bacteroidetes, and Firmicutes. Redundancy analysis showed that the soil bacterial community was mainly influenced by soil organic carbon, dissolved organic carbon, microbial biomass carbon, available P, and available K. In summary, early rice returning could increase soil available K and K content in late rice. Early rice straw returning with reducing potassium fertilizer had no negative impacts on the growth and yield of late rice and could also improve soil organic carbon and the diversity of soil bacteria. Therefore, early rice straw returning with reducing potassium fertilizer can guarantee the grain yield of late rice and improve soil fertility.