Objective To evaluate the characteristics of agricultural non-point source (NPS) pollution in small watersheds upstream of the Danjiangkou Reservoir, identify its key pollution sources, and support targeted pollution control strategies, this study takes the Yahe River small watershed in Xichuan county, Nanyang city, Henan province as the study area.

Methods Based on field survey data, the inventory analysis method and the equivalent pollution load method were employed to systematically estimate the nitrogen and phosphorus pollution loads from agricultural non-point sources. The emission structure, spatial distribution, and contribution rates of different pollution sources were further analyzed.

Results 1) Chemical fertilizer application was the primary source of nitrogen and phosphorus pollution, with an equivalent pollution load of 30.661 6 × 10⁶ m³, accounting for 68.08% of the total load. This was followed by livestock farming (7.425 1 × 10⁶ m³, 16.48%) and rural domestic pollution (6.501 8 × 10⁶ m³, 14.44%). Agricultural solid waste made a minimal contribution, representing only 1% of the total load. 2) The intensity of NPS pollution showed a clear increasing trend from upstream to downstream. The upstream sub-basins (3 and 4) contributed 12.52% of the total pollution load, the midstream sub-basins (2 and 5) contributed 32.14%, while the downstream sub-basins (0 and 1), with the most intensive human activities, contributed 55.34%, identifying them as the critical areas for pollution control.

Conclusions Total nitrogen pollution is prominent in the watershed. Governance priorities are defined according to pollution sources and spatial distribution. Excessive fertilizer application is the main cause. Fertilizer reduction and livestock manure recycling are core measures, providing references for similar watersheds in the upper Danjiangkou area.