study of the relationship between slope of retention curve and some physical properties of soil quality

abstract different definitions have been proposed for soil quality. various soil properties have been suggetsted as soil quality indices by researchers. this research was conducted to study the relationship between slope of retention curve at its inflection point (s index) and other soil physical quality indices, because the reserches between s index and soil physical properties are little. thirty five soil samples were collected and some physical and chemical properties measured . the moisture contents were measured at 0, 1.5, 2.5, 5.5, 10, 20, 30, 50, 100, 200, 300, 500, 1000 kpa pressure heads. the parameters of van genuchten equation (1980) were determined by using of retc software. the slope of retention curve at the inflection point were determined and it was considered as soil physical quality index (s). then the relationship between s index and soil physical properties was determined by spss software. according to the s index and penetration resistance (pr), it seems that the physical quality of studied soil samples was suitable for accesssing. also there was a significant correlation between s index with mean weight diameter (mwd), clay percentage, sodium absorption ratio (sar), organic matter percentage, electrical conductivity (ec), least limiting water range (llwr), available water content (awc), and penetration resistance (p<0.01). in addition the correlation between s index with bulk density and calcium carbonate was significant at p<0.05. among the studied parameters, the correlation between s index with clay percentage, bulk density, ec, and penetration resistance was negative and s index had a direct relation with other soil properties.