Assessment of coastal soil fertility based on environmental impact: a case study in the Yellow River Delta, China

Deltas face the dual effects of estuary sedimentation and coastal erosion, greatly threatening to its soil fertility. Based on soil sampling data from July 2019 in the Yellow River Delta, a geographically weighted regression (GWR) model was applied for spatial interpolation. Fertility assessment of each indicator was performed using the ecological quality ratio (EQR), and the results were then used to calculate the spatial Nemoro quality index (NQI). The NQI in the study area was 0.39, corresponding to "III. Generally fertile". The eastern coastal NQIs were the lowest. Arable land and garden land were the two types of land use with the highest NQIs. EQRs of arable land, woodland, grassland, and garden land ranked in the order pH > total phosphorus > total potassium > salt content > total nitrogen > organic matter. Geodetector results showed that soil type and land use influenced soil NQI significantly. Secondary land use classification better promoted the influence on soil fertility than did the primary land use category. Therefore, in the Yellow River Delta, future agricultural planning should necessitate focusing on organic matter and nitrogen status to improve land productivity, especially in eastern coastal areas. Thus, more detailed and rational land use management policies should be implemented to improve soil fertility.