Evaluation and obstacle analysis of cultivated horizon soil quality based on MDS in the dry farming areas of Huang-Huai-Hai Region

Cultivated horizon soil quality is one of the most comprehensive indexes to represent soil fertility and production capacity. In this study, a systematic evaluation and obstacle analysis was performed on the cultivated horizon soli quality using a minimum data set (MDS). The study area was located in the dry farming region of Huang-Huai-Hai in the middle of eastern China, which was one of the most important grain-producing areas in China. The samples were collected from May to June 2017. A total of 270 sampling points were set as the stratified sampling of 0-40 cm with 10 cm as each sampling layer. The soil type was considered to determine the quality level of arable land, the cropping system, and the degree of concentrated contiguity. A series of experiments were then carried out to measure each index. A total of17 evaluation indicators were selected to investigate the characteristics of cultivated horizon soil using the soil's physical and chemical properties, as well as the tillage profiles. The soil management framework was used to construct the total data set (TDS). The affiliation function between the indicators and cultivated horizon soil quality was established using the positive and negative effects of each evaluation indicator on cultivated horizon soil quality. The evaluation system of cultivated horizon soil quality was established using principal component analysis (PCA). The multiple indicators were transformed into a small number of indicators using PCA, in order to reduce the dimensionality for the representative independent evaluation indicators in the MDS. The weights of each evaluation indicator were further determined to extract the common factor variance of evaluation indicators. Then the evaluation index systems of TDS and MDS were used to calculate the cultivated horizon soil quality index respectively. Specifically, the cultivated horizon soil quality index served as a comprehensive quantitative description of the condition of cultivated land. The productivity of soil was evaluated to provide a strong reference for the reasonable cultivated layer construction. The scatter plot of the cultivated horizon soil quality index was fitted in the total and the minimum data set, indicating a significantly positive correlation (R²=0.61, P less than 0.05). By contrast, the Nash effective coefficient and relative deviation coefficient of the cultivated horizon soil quality index were also calculated to be 0.601 and 0.181, respectively. The comprehensive analysis showed that the cultivated horizon soil quality index of the total data set was closer to that of the minimum data set with a smaller relative deviation and higher accuracy. Consequently, the MDS can be expected to better replace the TDS as the cultivated horizon soil quality index. Six indicators were selected for the MDS evaluation index system by principal component analysis (PCA), including the soil organic matter, soil cation exchange capacity, soil pH, plough layer thickness, penetration resistance of plough layer, and the compactness degree of plough layer. The cultivated horizon soil quality index ranged from 0.25 to 0.61 with an average value of 0.43, which was generally at a medium level. There was a significant positive correlation between grain yields and the quality index. The reasonable threshold of the cultivated-layer quality index was achieved as follows: the plough layer thickness not less than 17.20 cm, the penetration resistance of the plough layer not greater than 896.10 kPa, the degree of compactness of plough layer not less than 78.01%, the soil organic matter content not less than 17.87 g/kg, the soil pH of 8.01-9.37, and cation exchange capacity not less than 21.13 cmol/kg. The types of barriers were divided into soil structure and nutrient barriers (category 1), nutrient barriers (category 2), and soil structure barriers (category 3). Specifically, the main obstacles were determined as the low content of soil organic matter, the low cation exchange capacity, and the higher compaction of plough layer. Therefore, the tillage and fertilization measures should be taken for the above obstacles. The finding can provide theoretical support to improve the cultivated horizon soil quality in the dry farming region of Huang-Huai-Hai in eastern China.