The effect of soil erosion on the Slope of moisture curve at inflection point (S index)

One of the important effects of erosion is physical degradation of soil, which can lead to reducing of soil quality. The slope of the moisture curve at inflection point, known as the S index, is an important indicator of soil physical quality. The higher S index, indicates the proper soil structure and proper soil conditions in terms of water and air circulation and plant growth. In this study, to determine the effect of erosion on soil quality, 30 gullies were selected from 3 region of Ardebil province. Then disturbed and undisturbed soil samples were taken from 1 meter and 50 meters distances of gullies wall at 4 points along each gully. Therefore totally 120 soil samples (60 pairs) were taken, half were near gullies and were affected by linear erosion effects and half distanced from gullies and did not directly affect by soil erosion. Soil moisture was measured at 0, 0.05, 0.1, 0.3, 0.5, 1, 3, 5, 10 and 15 Bar by pressure plate and falling head instrument. Then soil moisture curve was determined by RETC6 software and S index of each soil sample determined. The S index mean in three studied areas for eroded soils (1m distance from gullies wall) was 0.06, 0.09 and 0.04, respectively and in the soil without erosion (50m distance from gullies wall) were 0.085, 0.12 and 0.06 respectively. Mean comparison with Paired t-test method between S index of soil samples adjacent gullies and distanced from gullies shows that S index in soils with linear erosion is significantly less than soil without erosion. Therefore concluded that gully erosion can be reduced the physical quality of adjacent soil and cause soil degradation.

Keywords:

Soil quality , Gully erosion , Soil degradation