Impact of organic substitution on greenhouse gas emissions and net warming potential during the winter wheat season in Shajiang black soil

Organic substitution has strong potential for carbon sequestration and sink enhancement. However, the cooling effect of organic substitution is significantly influenced by soil type and climatic conditions. Despite this, there remains a lack of targeted studies on how high substitution ratios can account for crop yield and emission reduction in typical soil areas. In this study, Shajiang black soil was used as the research object. Treatments included no fertilizer (CK), pure fertilizer (OPT), and varying levels of organic (chicken manure) substitution (1/4M, 1/2M, 3/4M and M). A two-year soil enrichment experiment was conducted, and greenhouse gas (GHGs) emissions were monitored during two fertilization periods in the wheat season of the second year. The results showed that soil organic carbon increased significantly with an increase in the organic replacement ratio, but the annual carbon sequestration efficiency (SOCSR) declined. The N₂O emissions initially increased and then decreased with an increase in the substitution amount. In particular, the 1/4M treatment produced the highest N₂O emissions, followed by the OPT and 1/2M treatments, whereas the CK and M treatments showed the lowest emissions. Among the cumulative emissions of CH₄, except for the 1/4M treatment which was the lowest and the OPT treatment which was the highest, the differences in the other treatments were not significant, and the overall level was not high. By combining the N₂O, CH₄, and soil carbon sequestration efficiency (SOCSR), the net warming potential (Net-GWP) of farmland under high organic substitution (M) treatment was –5 097.6 kg(CO₂-eq)·hm^–2, which was significantly lower than that of other treatments. This was followed by 3/4M and 1/2M treatments, with Net-GWP values of –3 523.1 and –2 541.7 kg(CO₂-eq)·hm^–2, respectively. In contrast, the Net-GWP of OPT and 1/4M treatment was relatively high, at –879.1 and –501.1 kg (CO₂-eq)·hm^–2, which was significantly higher than that of other treatments (except CK). The Net-GWP initially increased and then decreased with organic substitution from zero to full substitution. In addition, N₂O emissions and CH₄ absorption in the wheat base fertilizer period were significantly higher than those in the topdressing period. N₂O emissions during the base fertilizer period accounted for 58.1%–66.7% of the total emissions, and CH₄ absorption in the base fertilizer period accounted for 55.3%–60.0% of the total absorption. Among the different treatments, the wheat yield of the 1/2M treatment was the highest, followed by that of the 1/4M treatment, 3/4M, and OPT treatments, whereas the total substitution (M) and CK treatments had the lowest yield. This study concludes that the short-term application of 50% chicken manure substitution not only maintains wheat yield in Shajiang black soil, but also enhances carbon sequestration and reduces emissions. Therefore, it is the optimal replacement ratio for achieving comprehensive economic and ecological benefits in Shajiang black soil wheat fields.