The Study Of Soil Quality Indicators And Its Assessment Based On Field Scale

In order to improve the accuracy of assessment of cultivated land quality and make evaluation results reflect the changes in land, the assessment method of soil quality based on field scale were studied. Taking Yangling town of Guanzhong district in Shanxi as an example, the methods of field investigation, data collection, sample collection, interior analysis, statistical analysis and mathematical modeling were used in the study. The method of principal components analysis (PCA) was used to establish the minimum data set (MDS) for soil assessment. The weight value for soil quality evaluation was determined using the method of PCA and fuzzy analytic hierarchy process (FAHP). The fuzzy comprehensive appraisement and soil quality index were used to evaluate the soil quality. Meanwhile, taking long-term field experiment as example, the methods of soil quality assessment such as soil quality index, factor analysis and cluster analysis were conducted in the study. The main results are as follows:1) The 27 soil samples were collected from the 0–20 cm soil depth. The minimum data set (MDS) components including organic matter, total nitrogen, total phosphorus, total potassium, available phosphorus, available potassium, CEC and calcium carbonate were selected through principal components analysis (PCA). The results of fuzzy comprehensive appraisement of soil quality fuzzy analytic hierarchy process (FAHP) showed that the evaluation results matched basically with real situation of cultivated land in study region. The study indicated that the method of fuzzy comprehensive appraisement was feasible under field scale. The results of quantitative evaluation of soil quality based on PCA indicated that the integrated fertility index was between 0.7 and 0.8 based on field scale.2) A long-term tillage trial was started in 2001, with the aim of investigating the effect of tillage patterns on soil physical, chemical, and biological properties as well as grain yield in a winter wheat-summer maize rotation. The trial was conducted on the Guanzhong Plain, Shaanxi Province. The objective of this study was to compare the soil quality index (SQI) among five tillage treatments: subsoil tillage (ST), rotary tillage (RT), straw return (SR), no-till seeding (NTS) and traditional tillage (TT). The ST, RT, SR, and NTS treatments were considered as conservation tillage treatments. Soil samples were collected from the 0–20 cm soil depth in 2008 and analyzed for organic matter (OM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkali-hydrolysis nitrogen (AN), available phosphorus (AP), available potassium (AK), urease, alkaline phosphatase, bulk density (BD), pH, electrical conductivity (EC), cation exchange capacity (CEC), and CaCO3. Components of the minimum data set (MDS) were chosen using principal component analysis (PCA). The methods of soil quality index, factor analysis and cluster analysis were used to evaluate the effects of conservation tillage patterns on soil quality. Results showed that after nine years of tillage, soil fertility and physical properties were better in the conservation tillage treatments compared to the TT treatment. In addition, urease and alkaline phosphatase activities were significantly greater in the conservation tillage treatment compared with the TT treatment. In terms of grain yield, winter wheat and summer maize yields were greatest in the ST, RT, and SR treatments followed by the NTS treatment, and the TT treatment. The conservation tillage treatments increased wheat yield by 13%-28% and summer maize yield by 3%-12% compared to the TT treatment.3) The value of weighted integrated soil quality index varied from 0.6978～0.8388 under CT and was 0.5826 in TT treatment. It suggested that conservation tillage improved soil quality. Soil quality indices were 19.8%-44.0% greater in the conservation treatments compared with the TT treatment. This suggests that conservation tillage improved soil quality. The results indicated subsoiling every other year, a combined operation of straw chopping with rotary tillage, and a combined operation of straw mulching with subsoiling not only increased crop yield, but also improved soil quality. Based on the economic and ecological benefits, the practices of subsoiling and straw return should be promoted. Correlation analysis showed that the SQI was closely correlated with final yield. This indicates that the SQI index can adequately evaluate soil quality under various tillage systems.4) The results of factor analysis indicated that twelve quantitative indicators including organic matter (OM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkali-hydrolysis nitrogen (AN), available phosphorus (AP), available potassium (AK), urease, alkaline phosphatase, bulk density (BD), pH, electrical conductivity (EC), cation exchange capacity (CEC), and CaCO3 related to soil property were chosen based on a long-term experiment. Five soil quality factors were summed up from 12 soil chemical, physical and biological attributes, i. e., the capacity of maintenance and supply of soil nutrients, organic, phosphorus, bulk density, enzyme activity with the method of factor analysis. The results of factor scores show that there are significant differences in superiority of five common factors in different tillage pattern. Soil quality scores of conservation tillage (CT) are higher compared with traditional tillage (TT), showing that soil physics, chemistry, biological properties and soil quality are improved in conservation tillage. The top three integrated teams with the highest scores are subsoiling to 30 cm after a year's interval (NS2), a combined operation of straw mulching and subsoiling to 20 cm, rotary tillage (SR2) and subsoiling to 30 cm every year (NS3). It indicates that the prominent advantages of subsoiling to 30 cm, rotary tillage and a combined operation of straw return and rotary tillage in improving soil structure, soil fertility and soil quality are outstanding.5) Cluster analysis shows that there are small differences in soil quality under the condition of the same conservation tillage technology and soil quality is more sensitive to tillage measurement than to technology of straw return.