Boosted Regression Tree-based Identification of Environmental Factors Influencing Gaseous Nitrogen Loss in Peanut Field on Red Soil Arid Hillside

To clarify the characteristics and influencing factors of gaseous nitrogen (N₂O and NH₃) loss in peanut field on red soil arid hillside, aeration method and closed static opaque chamber-gas chromatography (GC) methods were adopted. In situ monitoring was carried out to reveal the dynamic change characteristics of NH₃ volatilization and N₂O emission of the peanut field on red soil arid hillside under conditions of plowing and no-tillage. Their key influencing factors were identified based on boosted regression tree (BRT) method. The results show that: (1) The variation range of NH₃ volatilization rate (measured in N) during the whole peanut growth period under plowing and no-tillage conditions was 0.02-1.55 and 0.02-1.05 kg·hm^-2·d^-1, respectively, the cumulative volatilization was (17.19±8.56) and (18.38±7.41) kg·hm^-2, respectively, accounted for (11.77±5.86)% and (12.59±5.08)% of the N application, respectively, and the NH₃ volatilization was concentrated within 15 d after base fertilizer application. The variation range of N₂O emission flux under plowing and no-tillage conditions was 0.07-2.90 and 0.02-3.97 mg·m^-2·d^-1, respectively, the cumulative emission was (0.81±0.27) and (0.68±0.10) kg·hm^-2, respectively, accounted for (0.55±0.17)% and (0.46±0.06)% of the N application, respectively, and the hot period of N₂O emission flux was not obvious. No significant difference in NH₃ volatilization between two tillage treatments were found, while no-tillage reduced cumulative N₂O emission by 16.05%. Ammonia volatilization was the main way of nitrogen gas loss in peanut field of red soil arid hillside. (2) The BRT analysis findings, soil ammonium-nitrogen content, days after fertilization, peanut growth period, rainfall in the previous 3 days, soil nitrate-nitrogen content were identified as the key factors affecting ammonia volatilization of the peanut filed on red soil arid hillside. The contribution rates were 47.92%, 14.78%, 8.21%, 7.44% and 5.91%, respectively. However, the key influencing factors of N₂O emission and their relative contributions were soil moisture (24.67%), soil ammonium-nitrogen content (20.34%), ground temperature (12.26%), rainfall in the previous 3 days (9.93%), soil nitrate-nitrogen content (9.91%), days after fertilization (9.64%), and temperature (8.51%). The above results show that fertilization is an important factor affecting the gaseous loss of nitrogen fertilizer in peanut field of red soil, and the highest loss of gaseous nitrogen (NH₃ and N₂O) accounted for 18.35% of the N applied. Microbial nitrification process and its environmental control factors may play an important role in soil nitrogen loss. These results could provide a theoretical basis for improving nitrogen utilization rate and mitigating environmental pollution in hillside agriculture in red soil region of South China.