Effects of green manure incorporation combined with nitrogen fertilizer reduction on soil respiration and its temperature sensitivity in regard to wheat fields

This study was conducted to explore the effects of green manure incorporation combined with nitrogen fertilizer reduction on the soil respiration dynamics of wheat fields and wheat yield in oasis irrigation areas. This study was performed to provide a theoretical basis for the study of carbon emission reduction in farmlands in arid oasis irrigation areas. The experiment was conducted in 2021 and 2022 in the Hexi Oasis irrigation area. With the conventional nitrogen application without green manure (N₁₀₀) as the control, we performed the following treatments: 15 000 kg∙hm⁻² green manure +85% nitrogen fertilizer (G₁N₈₅), 22 500 kg∙hm⁻² green manure +85% nitrogen fertilizer (G₂N₈₅), 30 000 kg∙hm⁻² green manure +85% nitrogen fertilizer (G₃N₈₅), 15 000 kg∙hm⁻² green manure +70% nitrogen fertilizer (G₁N₇₀), 22 500 kg∙hm⁻² green manure +70% nitrogen fertilizer (G₂N₇₀), and 30 000 kg∙hm⁻² green manure +70% nitrogen fertilizer (G₃N₇₀). There were seven treatments in total. Soil respiration rate, carbon emissions, yield, and carbon emission efficiency during the wheat growth period were explored, and the response of soil respiration to soil temperature was analyzed. The results showed that the soil respiration rate under different treatments showed a single-peak trend of initially increasing and then decreasing, and the variation range was 0.8 to 6.2 μmol∙m⁻²∙s⁻¹ during the whole growth period. The combination of green manure incorporation and nitrogen fertilizer reduction significantly increased the soil respiration rate and the total soil carbon emissions of wheat fields. When compared with N₁₀₀, the average increases were 7.2%−19.8% and 5.7%−18.8%, respectively. G₃N₈₅ and G₃N₇₀ increased the soil respiration rate by 2.3%−16.0% and 3.3%−19.8%, the total soil carbon emissions by 2.9%−15.2% and 3.1%−18.8%, respectively (P<0.05), when compared with the other treatments. Compared to G₃N₈₅, the average soil respiration rate and total soil carbon emissions of G₃N₇₀ treatment increased by 3.3% and 3.1%, respectively (P<0.05). Green manure incorporation combined with nitrogen fertilizer reduction significantly decreased the temperature sensitivity of soil respiration (Q₁₀), and when compared with N₁₀₀, the Q₁₀ values decreased by 10.4%−18.1% (P<0.05). Green manure incorporation combined with nitrogen fertilizer reduction could significantly affect wheat yield and soil carbon emission efficiency, with the G₃N₈₅ treatment significantly higher than the other treatments by 4.2%−45.6% and 0.3%−26.4% (P<0.05). In conclusion, green manure incorporation combined with nitrogen fertilizer reduction enhanced the soil respiration of wheat fields while reducing the temperature sensitivity of soil respiration. It also improved wheat yields and carbon emission efficiency. Green manure incorporation at 30 000 kg∙hm⁻² combined with nitrogen fertilizer reduction by 15% (G₃N₈₅) proved to be an effective way for nitrogen reduction and emission mitigation while improving soil productivity for wheat fields in Hexi Oasis irrigation area.