Effects of crop patterns and straw management on greenhouse gas emissions in paddy fields

A 1.3 hm² paddy field was selected in Jiashan County, Zhejiang Province, and four treatment groups, briefly referred to as water-saving irrigation, water-saving non-returning, ordinary returning, and ordinary non-returning, were set up with two planting modes, namely water-saving drought pipe + straw returning/non-returning and ordinary inundation irrigation + straw returning/non-returning. The methane (CH₄) and nitrous oxide (N₂O) emission data from 336 rice fields in 28 batches obtained by static box gas chromatography, in combination with the analysis results of 12 samples of 6 environmental factors, including soil particulate organic carbon (POC), were used to explore the influence of planting mode and straw management on greenhouse gas emission characteristics of rice fields. The results showed as follows: (1) The cumulative CH₄ emissions were in the order of ordinary returning > ordinary non-returning > water-saving returning > water-saving non-returning, and the cumulative N₂O emissions were in the order of ordinary returning > water-saving non-returning > water-saving returning > ordinary non-returning. The global warming potential (GWP) and greenhouse gas emission intensity (GHGI) of ordinary returning group were the highest, being 7 696.03 kg/hm² (calculated as CO₂) and 0.97 kg/kg, and those of water-saving non-returning group were the lowest, being 2 110.12 kg/hm² and 0.21 kg/kg, respectively. (2) The analysis results of the least significant difference method showed significant differences in cumulative CH₄ emissions among the treatment groups. According to Pearson correlation analysis, the cumulative CH₄ emission was extremely significantly positively correlated with POC content (P <0.01) and significantly positively correlated with microbial carbon content (P <0.05). The cumulative emission of N₂O was significantly positively correlated with \mathrmNO_3^- -N content (P <0.05), and GWP and GHGI were extremely significantly positively correlated with POC content (P <0.01). (3) Both planting mode and straw management had extremely significant effects on CH₄ cumulative emissions (P <0.01), and their interaction had significant effects on CH₄ cumulative emissions and N₂O cumulative emissions (P <0.05). The research shows that rice water-saving and drought-tube planting combined with straw returning is a climate-friendly high-yield and economic planting model, which can ensure food security, reduce the cost of straw leaving the field, and play a positive role in slowing down the global greenhouse effect.