Soil-quality-index model for assessing the impact of groundwater on soil in an intensively farmed coastal area of E China

Soil quality is important in measuring sustainable land-use and soil-management practices. It is usually assessed by evaluating important physical, chemical, and biological soil properties. For this study, a site-specific 22 variables representing pertinent soil (0-10 cm) and groundwater properties were selected as potential soil-quality indicators in a coastal salt-affected farmland of E China. To investigate the role of groundwater in soil-quality assessment, we designed two sets of minimum data sets (MDSs). Minimum data set 1 (MDS1) had inputs of the 19 soil chemical and physical properties whereas MDS2 was based on the 22 soil and groundwater properties. Using principal-component analysis, discriminant analysis, and soil-quality-index (SQI) model, we demonstrated the procedures of MDS selection, indicator normalization, and integration of MDS into SQI value for soils used for the two cropping systems. Results indicated selection of SOCD, AK, and ρb as MDS1 indicators but MDS2 indicators included SOM, SOCD, Cl, Na, WTg, and ECg. These were found to be the most effective discriminators between the two cropping systems. Available K (AK) made greatest contribution to SQI using MDS1 indicators, however, WTg, ECg, and Cl were the greatest contributors to the SQI for MDS2. Contribution of SOCD to SQI was severely inhibited in cotton-barley rotation system while ECg and WTg contributions to SQI were inhibited in rice-rape rotation system. In general, cotton-barley rotation system had a better soil quality over rice-rape rotation system as the former had higher SQI values than the latter for both MDSs. Crop parameters did also exhibit significant relationship with the SQI values using MDS2 but it was not significant for MDS1. Our results suggest that in addition to soil chemical, physical, and biological indicators, groundwater properties particularly the WTg and ECg are also important for assessing soil quality in an intensively farmed coastal area.