Assessing non-point source pollution in an apple-dominant basin and associated best fertilizer management based on SWAT modeling

Investigating the impact of apple-dominated areas on nitrogen (N) and phosphorus (P) losses at a basin scale was essential for the sustainable development of apple industry in China. This study conducted a survey on fertilizer application and built a Soil and Water Assessment Tool (SWAT) model to quantitatively analyze the N and P losses in the Qixia apple-dominated area. Additionally, the decreases in N and P losses through adjusting the fertilizer application modes were evaluated. Results showed that average N and P losses in the Wulong River Basin (WRB) were 44.4 and 0.365 kg ha⁻¹ in 2011–2017, respectively, and apple orchards accounted for 73.3% and 51.4% of the total N and P losses in the basin. Under nine fertilizer scheduling scenarios, three fertilizer schedule scenarios, automatic fertilizer application (S-AUTO), “one shot” mode (S1), and regulated fertilizer application (S-BSD), had the lowest N and P losses in apple orchards. The decreases in N loss ranged from 20.6% to 26.1% at the subbasin scale and 14.8%–30.7% at the basin outlet when applying the S-AUTO, S1, and S-BSD fertilizer application modes in Qixia apple orchards and all apple orchards in the WRB. The reductions in P loss varied from 22.0% to 46.1% at the subbasin scale and 14.6%–25.6% at the basin outlet. In orchard-dominated basin, N and P losses can be effectively reduced by optimizing the orchard fertilizer scheduling strategies.