Integrating low levels of organic fertilizer improves soil fertility and rice yields in paddy fields by influencing microbial communities without increasing CH4 emissions

Abstract

Although organic fertilizer is usually recommended for improving soil quality and crop yields, it inevitably enhances methane (CH4) emissions. Effective measures to mitigate CH4 emissions while ensuring crop yields are urgently needed. A two-year experiment was performed to examine the effects of organic-inorganic fertilizer combinations on CH4 emissions, the CH4-related microbial community, soil biochemical characteristics, and rice yields during dual rice growing seasons in 2020–2021 at two locations (i.e., Nanning and Yulin City, Southern, China). The treatments were as follows: no N fertilizer (Neg-CF), 100 % chemical fertilizer (CF) (Pos-CF), 60 % cattle manure (CM) + 40 % CF (High-CM), 30 % CM + 70 % CF (Low-CM), 60 % poultry manure (PM) + 40 % CF (High-PM), and 30 % PM + 70 % CF (Low-PM). CH4 fluxes and related functional microorganism abundances were investigated using the closed chamber method and molecular procedures, respectively. The addition of organic manure significantly improved rice grain yields and soil properties, including total nitrogen (TN), soil organic carbon (SOC), and pH compared to the Pos-CF. Similarly, integrating organic and inorganic fertilizers led to significant increases in seasonal CH4 emissions, global warming potential (GWP), and the abundance of CH4-related soil microbes. Average increases in SOC, TN, CH4 emissions, and GWP in the High-PM treatment relative to the Pos-CF were 44.7, 36.4, 20.6, and 24.4 %, respectively, in Nanning; and 28.9, 33.3, 23.4, and 20.8 % in Yulin City, averaged across the years. Moreover, co-fertilization resulted in the highest increase in methanogenic diversity and abundance relative to Pos-CF only. Applying high proportions of manure improved the abundance of methanogenic soil archaea related to CH4 production compared with the plots with low proportions of manure. Interestingly, lower manure amendments produced the highest rice grain yields and lowest CH4 emissions while maintaining high soil qualities. In addition, regression analysis exhibited that SOC was highly positively associated with CH4 emissions. Above all, controlling the proportions of organic manure and CF may be a feasible approach for enhancing rice yields and soil quality while mitigating CH4 emissions. Of the treatments tested, the combination of 30 % organic manure (i.e., CM or PM) with 70 % CF (urea) performed the best. This study showed that combining manure and CF at a 30:70 ratio was the most effective approach for improving soil health and rice yields while ensuring environmental sustainability.