Background The gully reclamation project has effectively solved the problems of farmland resource constraints and human-land conflicts on the Loess Plateau, but its interception effect and mechanism on erosion-based non-point source pollution are still unclear.

Methods Water samples were collected from a typical untreated watershed (Shengli River) and a ditch-cultivated watershed (Gutun River)and an ecological interception ditch (Nangou), and soil samples were collected from typical newly-created lands and adjacent sloping lands, and the nitrogen (N) and phosphorus (P) contents were measured, and the data were processed using Origin and Excel software.

Results 1) The soilN andP content in the newly-created land with continuous cultivation increased, and the N and P content of itscultivated soil layer was significantly higher than that of the sloping land (P < 0.05), and the N infiltration rate of the newly-created land was higher than that of the sloping land. 2) The total reduction rates of water total nitrogen (TN), total phosphorus (TP), nitrate nitrogen (NO₃^--N), and ammonia nitrogen (NH₄⁺-N) by the three-stage ecological interception dam reached 44.3%, 94.8%, 91.2%, and 46.9%, respectively. 3) The runoff in different periods of the sub-basin was ranked as Annual season>Wet season>Dry season, which was consistent with the pattern of regional precipitation, and the runoff of the untreated watershed was 29 times of the treated watershed. 4) The changes in water TP, TN, NO₃^--N, and NH₄⁺-N contents in different periods were all ranked as Dry season>Annual season> Wet season. 5) Compared with the untreated watershed, the treated watershed intercepted the largest amount of TN, followed by NO₃^--N, and the smallest amount of TP.

Conclusions The results of the study show that the gully reclamation projectmay intercept the agricultural N and Pnon-point pollution from the source and in the process, which is conducive to improving the efficiency of chemical fertilizer use.