Green manure and rice straw recycling: A triple-win for productivity, environmental sustainability and net ecosystem economic benefit
Green manure and rice straw recycling is widely practiced in paddy soils of southern China to enhance soil fertility and crop productivity; however, its environmental consequences remain lacking. Here, we used a long-term field experiment to quantify greenhouse gas (GHG) emissions and associated microbial functional genes, energy-use efficiency, carbon footprint, and net ecosystem economic benefit to assess the sustainability implications of this practice. The treatments consisted of conventional chemical fertilizers (CK), CK + green manure recycling (M), CK + early-season rice straw recycling (ERS), CK + ERS + late-season rice straw recycling (DRS), CK + ERS + M (ERSM) and CK + DRS + M (DRSM). Compared with ERS, DRS and DRSM, the ERSM significantly reduced the annual cumulative methane (CH4) emissions by 24.3 %, 33.9 % and 22.1 %, respectively. Similarly, ERSM significantly reduced nitrous oxide (N2O) emissions by 18.5 %–34.2 % compared to the other treatments, except for DRS. However, compared with all the other treatments, the ERSM treatment increased annual grain yield by 6.0 %–67.6 %, energy-use efficiency by 6.8 %–68 %, and net ecosystem economic benefit by 10.9 %–112.1 %. Optimizing carbon-to-nitrogen ratio lowers direct GHG emissions through balancing CH4-related gene activity (mcrA and pmoA) and by promoting ammonia-oxidizing genes (amoA), which in turn reduced carbon footprint. Soil organic carbon storage and CH4 via direct-GHG emissions and chemical nitrogen via indirect-GHG emissions were the major contributors to carbon footprint. In conclusion, ERSM is an effective strategy to promote sustainable rice production in rice-rice cropping systems and it has the potential to support carbon neutrality efforts.
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