Legume straw incorporation with optimal nitrogen fertilizer improves soil quality and reduces the carbon footprint of farmland ecosystems in semiarid areas

Optimizing nitrogen fertilizer and straw application is essential for sustainable agricultural development. However, the effects of variations and related factors associated with nitrogen fertilizer reduction combined with different straws on soil quality and greenhouse gas emissions remain unclear. Hence, a two−year field experiment was conducted to comprehensively assess the effects of nitrogen fertilizer application rate and different straws incorporation on maize growth, the soil quality index (SQI), direct global warming potential (GWP direct ) and carbon footprint (CF). The treatments included: no nitrogen fertilizer (CK), conventional nitrogen fertilizer 225 kg ha −1 (N 225 ), 20 % reduction of conventional nitrogen fertilizer (N 180 ), N 180 with soybean straw incorporation-legume crop straw (SN 180 ) and N 180 with maize straw incorporation-gramineous crop straw (MN 180 ). Results revealed that the N 180 treatment produced comparable yield to that of the N 225 treatment and significantly increased nitrogen agronomic efficiency (NAE) by 16.54 %–16.98 %; however, SOC content decreased by 0.12 g kg −1 . Compared with N 180 , the SN 180 treatment significantly increased the SQI by 9.20 % in 2022 and 10.76 % in 2023, and the MN 180 treatment increased the SQI by 3.19 % in 2022 and 8.69 % in 2023, respectively. Although the SN 180 and MN 180 treatments had higher the GWP direct by 92.60 %–95.31 % and 49.67 %–53.51 % than the N 225 treatment, the greater SOC sequestration rate (0.54 and 0.37 Mg C ha −1 y −1 ) and lower N application rate in these treatments resulted in substantial decreases in the CF of 72.05 %–73.50 % and 48.81 %–49.42 %, respectively. Mantel tests and partial least squares path modeling (PLS−PM) revealed that the higher SQI and N 2 O emissions in the SN 180 than MN 180 treatment were driven mainly by higher Nmin (13.01 %–19.88 %) and MBN (5.28 %–7.09 %) contents, and Pacq (3.11 %–14.82 %) enzyme activity. Overall, 20 % reduction of conventional nitrogen fertilizer with legume straw incorporation was more effective at improving soil quality and reducing environmental pollution, providing guidance for sustainable development in semiarid farmland ecosystems. ● 20 % N reduction showed comparable yield than conventional N application. ● Optimal N fertilizer with straw incorporation improved the soil quality index (SQI). ● Straw incorporation markedly decreased carbon footprint due to augmented SOC stock. ● Legume straw had greater effects on the SQI and carbon footprint than maize straw.