Evaluation of soil quality in major grain-producing region of the North China Plain: Integrating minimum data set and established critical limits

Understanding of the nexus between soil quality (SQ) and productivity, the heterogeneity of SQ and the re-stricting indicators that affect crop productivity is essential for a specific region to encourage improving of SQ while contributing to profitable crop production. The objectives of this study were to develop minimum dataset (MDS) variable selection methods that reflects the total dataset (TDS) of soil properties for SQ assessment and crop yield prediction in Yucheng County, a major grain-producing region in the North China Plain. Critical values of soil properties for standardized scoring functions were established based on local crop yields in field condition and the key restricting indicators limiting crop productivity were evaluated. In this study, 99 topsoil (0-20 cm) samples were collected and 14 soil properties including pH, electrical conductivity, clay content, soil organic matter, cation exchangeable capacity, total nitrogen, phosphorus (P) and potassium (K), available P, K, Cu, Mn, Mo and Zn were analyzed. Three MDSs were created by different variable selection methods using principal component analysis (PCA) of soil properties. Among these MDSs, the indicator of norm values derived from the total principal component loadings was considered to be the most suitable method for evaluating SQ. The MDS-based soil quality index (SQI) had higher correlations with the TDS-based SQI and crop yield. The critical values of soil properties were identified by regressing soil variables with local yields of maize and wheat in the field condition. The SQIs calculated using measured critical values were more accurate than that based on published empirical values. The evaluation results revealed that the calculated SQI accounted for 28% of the variation in crop yields, and there probably are some strong limitations for crop yield through soil characteristics (soil texture, salinization, and nutrient supply, etc.). Thus, management practices and amelioration of the above soil-limiting factors should be comprehensively considered in agricultural production. The finding can enable policy making and policy implementation in relation to SQ in the future.