[Soil Quality Evaluation and Obstacle Diagnosis of Saline-Alkali Cultivated Land in the Hetao Plain]

Soil quality of cultivated land determines food security and the development of farmland ecosystems. In this study, 16 soil physical and chemical properties were used to determine the characteristics of soil degradation index （SDI） and resistance index （SRI） in five typical areas of the Hetao Irrigation District in the middle and upper reaches of the Yellow River. Based on the total data set （TDS） and minimum data set （MDS）, the soil quality index （SQI） was calculated using six methods of membership function and linear （S_L） and nonlinear scoring （S_NL）. The difference and correlation of SQI values in different methods and the soil quality grade in each study area were discussed, and the soil obstacles in different study areas were clarified. The results showed that： ① The SDI value of EC in Hongsibu was the lowest （-265.84）, and the maximum value was AK in Huinong （60.37）. The SRI of soil TS in Hangjinhouqi was the lowest （0.634 7）, and the SRI of Huinong silt was the highest （0.878 8）. Soil EC, SAR, TS, and ESP were more sensitive to SDI and SRI. On the whole, the soil quality of the five study areas was significantly degraded. The mean values of SRI and SDI of all indicators were significantly correlated. ② MDS included five indicators of soil TN, EC, clay, pH, and AK, which could explain 76.46% of the 16 primary indicators in the whole data set. The average SQI calculated by the six evaluation methods were as follows： SQI（MDS-S_L）>SQI（TDS-MF）>SQI（MDS-MF）>SQI（TDS-S_L）>SQI（TDS-S_NL）>SQI（MDS-S_NL）. With SQI（TDS-MF） as the reference value, the SQI of each method was significantly correlated with it, and the correlation coefficient with SQI（TDS-S_NL） was the largest. In the scoring methods, the overall performance of S_NL was better than that of S_L, but its SQI value was small. ③ The soil quality of the whole study area was dominated by medium and low grades （accounting for 54.05% of the total area）； the soil grade of Hongsibu was the lowest （medium and low-grade soil accounted for 85.71%）. High and higher quality soil of Huinong accounted for the largest proportion （70.31%）. At present, the study areas were mainly faced with soil organic matter and nutrient limitation obstacles （especially Hongsibu）. There were also texture obstacles in Huinong, Wuyuan, and Hangjinhouqi and alkali stress in Xidatan. The research results can provide a scientific basis for the evaluation of the degradation degree and soil quality of saline-alkali farmland in the Hetao Plain and the selection of reasonable improvement measures.