Effects of gully erosion and gully filling on soil degradation in the black soil region of Northeast China

Gully erosion has caused soil degradation and even reduced soil productivity. However, only few studies on the effects of gully erosion and artificial controlling measures on soil degradation in the Black Soil Region of Northeast China are available. Thus, this study explores the relationships between gully erosion, gully filling and soil parameters. Two sets of soil samples were collected in the field at: (1) 72 sample points in the gully erosion study area, 60 sample points in the ephemeral and classical gully erosion area (3,518 m²), 12 sample points in the deposition zone (443 m²), (2)10 reference points along a slope unaffected by gully erosion representing the original situation before the gully was formed. All soil samples were analyzed for gravel content (GC), soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), and available potassium (AK). The soil property values on unaffected slope were fitted by the polynomial curves as the reference values in no gully erosion area. The interpolated soil property values in gully eroded study area were compared with these polynomial curves, respectively, and then, changes of soil property values were analyzed. Gully erosion caused an increase in GC and a decrease in SOM, TN, AN, AP and AK. The change of GC, SOM, TN, AN, AP, AK was 8.8%, ?9.04 g kg^?1, ?0.92 g kg^?1, ?62.28 mg kg^?1, ?29.61 mg kg^?1, ?79.68 mg kg^?1. The soil property values in the study area were below optimal values. Thus, we concluded that gully erosion and gully filling caused both on-site and off-site soil degradation. Soil degradation area was 0.65 % of the cultivated land. In addition, it was proved that gully filling were an improper soil and water conservation measure, which seems to exacerbate the problem. Thus, it is suggested that soil where soil is deep is moved to fill the gully, and then the area around the filled gullies should be covered by grass for preventing the formation and development of the gully.