Soil quality is a necessary indicator of land management. Different indices are applied to evaluate farming systems, soil types and land uses on soil quality. The slope of retention curve at its inflection point has been defined as soil physical quality index (Si) and so far the relationships between Si and penetration resistance (PR), the least limiting water range (LLWR), and available water content (AWC) have not been studied. In this study, I) the effects of soil physical properties on Si index and PR, and II) the relationships between Si index and PR, LLWR, and AWC were investigated. Seventy undisturbed soil samples were collected and the slope of inflection point for soil retention curve as a soil physical quality index (Si) was determined in each sample using soil retention curve data. Furthermore, PR was measured in soil surface, and LLWR and AWC were calculated. The results showed that the correlation coefficients between PR with water content, Electrical conductivity (ECe), SAR, and Si index were significant at P<0.01, whearas its correlations with bulk density (ρb), and organic matter (OM) were significant at P<0.05. There was also a negative correlation found between AWC and PR (P<0.01). In addition, a positive correlation between Si and LLWR, and negative correlation between PR and LLWR among soil samples (P<0.01) were found to exist. Therefore, the Si index provides a tool that can be used to compare different soils or the effects of different management practices on soil physical properties.

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