Green Manure Crops Combined with Enhanced-Efficiency Products Reduced Greenhouse Gas Emissions and Carbon Footprints in Dryland Wheat Fields

A field experiment was conducted to investigate the effects of green manure (GM) crops combined with enhanced-efficiency products on greenhouse gas emissions (GHGs) and carbon (C) footprints in the dryland summer GM-winter wheat rotation system on the Loess Plateau, so as to provide the theoretical basis and technical parameters for fully tapping the emission reduction and C fixation potential of GM crops, and evaluating its environmental benefits in this cropping system.

The GHGs patterns and net balance of soil C pool in summer GM-winter wheat rotation system of black beans (Phaseolus vulgaris L.) and rapeseed (Brassica napus L.) combined with different enhanced-efficiency products were measured from 2023 to 2024. There were 9 treatments, including: fallow (control), black beans sown alone, black beans + composite biological bacteria (Zaoyijia No.1), black beans + bacterium (Bacillus beresii B22), black beans + sepiolite, rapeseed sown alone, rapeseed + absorbent polymer (Shouke), rapeseed + actinomycetes (Streptomycete rochei D74), and rapeseed + sepiolite, each with 3 replications. C footprints were quantified and evaluated comprehensively, and the suitable GM + product combinations for C sequestration and GHGs emission reduction in drylands were screened.

(1) Compared with black beans sown alone, black beans + bacterium significantly reduced N₂O and CO₂ emissions, and global warming potential (GWP), with an average decrease of 29.3%, 17.5%, and 17.8%, respectively, reduced 21.6% GHGs intensity (P>0.05), and increased 7.8% wheat yield (P>0.05). (2) Black beans + bacterium showed the highest dry biomass(4 230 kg·hm^-2) and C input(1 750 kg·hm^-2) and decreased 43.6% (P<0.05) C footprints compared to fallow. (3) Compared with rapeseed sown alone, rapeseed + sepiolite significantly reduced N₂O and CO₂ emissions, and GWP, with an average decrease of 52.0%, 16.9%, and 17.6%, respectively. (4) Rapeseed + sepiolite showed the highest dry GM biomass(2 723 kg·hm^-2) and reduced 27.0% (P<0.05) C footprints compared with fallow.

Introducing the optimized mixture of black beans + bacterium and rapeseed + sepiolite into the summer GM-winter wheat system in the Loess Plateau effectively reduced the GHGs and GWP after incorporating the GM crops, boosted C input, and diminished the C footprints of the crop growth period. This study established a green and clean production model that promoted grain quality, fertilizer use efficiency, C sequestration, and emission reduction, and accelerated the high-quality development of "ecological priority, green and low-carbon" in drylands.