How Soil Pore Distribution Could Help in Soil Quality Studies as an Appropriate Indicator

The present study is aimed at examining the impacts of land use and slope gradient on pore space distribution as well as some soil physicochemical properties. Three land uses were considered in this research: natural forest lands, degraded forest lands, and cultivated lands as dry farming. The study area was divided into four slope classes. Furthermore, two types of soil surface (0-10 cm) sampling were performed: a) soil samples for physicochemical analysis and b) intact samples for thin section preparation and image analysis to extract pore equivalent diameter distribution. Pore diameters were divided into three classes, including macropores, mesopores, and micropores. One hundred and eight soil surface samples were collected from the study area. The results revealed that macropores and mesopores are predominant in the natural forest soils, while micropores are dominant in the cultivated soils. Moreover, the highest contents of soil organic matter (SOM) and cation exchangeable capacity and the lowest value of bulk density are observed in the natural forest soils. Regression analysis revealed a positive regression between SOM and macropores and mesopores and a negative regression between organic matter and micropores. These results indicated the importance of SOM in the formation of macropores and mesopores. It appears that plowing cultivated lands has led to the exposure and decay of SOM. In addition, agricultural machinery traffic affects soil compaction, both resulting in the formation of micropores. Overall, soil pore distribution has the essential sensitivity to detect changes in soil quality due to land use changes or other operations.