Effects of different organic fertilizers on nitrous oxide and methane emissions from double-cropping rice fields

Rice fields are a major source of greenhouse gases, such as nitrous oxide (N₂O) and methane (CH₄). Organic fertilizers may potentially replace inorganic fertilizers to meet the nitrogen requirement for rice growth; however, the simultaneous effects of organic fertilizers on N₂O and CH₄ emissions and crop yield in paddy fields remain poorly understood and quantified. In this study, experimental plots were established in conventional double-cropping paddy fields in the Pearl River Delta, China, including an unfertilized control and five fertilizer treatments with fresh organic fertilizer (FOF), successively composted organic fertilizer (SOF), chemically composted organic fertilizer (COF), COF supplemented with inorganic fertilizer (COIF), and chemical fertilizers (CFs) (TFOF, TSOF, TCOF, TCOIF, and TCF, respectively). Paddy field soils behaved simultaneously as an N₂O sink (cumulative N₂O emission: −196 to −381 g N ha^-1) and as a CH₄ source (cumulative CH₄ emission: 719 to 2 178 kg ha^-1). Compared to CFs, the effects of organic fertilizers on N₂O emission were not significant. In contrast, total annual CH₄ emission increased by 157%, 132%, 125%, and 37% in TFOF, TCOF, TSOF, and TCOIF, respectively, compared to TCF. In TCOIF, rice yield was maintained, while CH₄ emission was not significantly increased from the paddy fields characterized by a prolonged flood period. An important next step is to extend these field-based measurements to larger rice cultivation areas to quantify the regional and national-scale impacts on greenhouse gas emissions and to help determine the optimum practice for fertilizer use