Background Soil conservation function plays an important role in soil formation, vegetation fixation and water conservation. Since the implementation of the Grain for Green project (GFGP), soil erosion in China has been effectively controlled. The change of soil conservation function in Weihe River Basin (WRB) before and after the GFGP was quantitatively evaluated in this study.

Methods Based on the Sediment Delivery Ratio (SDR) module of the InVEST model, the soil conservation function of the WRB in 1980 and 2020 was evaluated using the data of rainfall erosivity (R), soil erodibility (K), vegetation coverage factor (C), DEM, and soil and water conservation measures factor (P). And the soil conservation amount under different land use types and slopes were counted in ArcGIS 10.2.

Results 1) After the GFGP, the soil erosion of the WRB was significantly improved. Compared with 1980, the actual amount of soil erosion in 2020 decreased by 1.40×10⁸ t, the average soil erosion modulus decreased by 1 033.51 t/(km²·a). The total amount of soil conservation increased from 48.60×10⁸ t to 53.73×10⁸ t. The soil erosion intensity has generally changed from a stronger level to a weaker level. The proportion of slight erosion increased from 60.75% to 77.43%. 2) Among different land use types, grassland had the largest soil conservation amount, accounting for > 40% of the total, while the largest amount of soil conservation per unit area was forestland. The soil conservation function of water area and unused land was relatively low. 3) The amount of soil conservation per unit area increased with the increase of slope within a certain range. The soil conservation amount in 0-5° micro slope area was the lowest. The area with >15°-25° steep slope has the largest amount of soil conservation, accounting for more than one third of the total soil conservation amount.

Conclusions After the implementation of GFGP, the soil conservation function of the WRB has been significantly improved. Land use and slope were two important factors affecting the soil conservation function. With the progress of vegetation restoration, the soil conservation function of different land use types and different slopes is gradually strengthened. The results provided a reference for quantitative evaluation of vegetation restoration effect and soil conservation function in the basin.