Soil erosion is one of the global environment problems, serious soil erosion could result in the loss of soil and water resource as well as land productivity in the cultivated slope land. The effect of various degree of soil erosion on the soil quality was studied, soil indicators sensitively responding to soil erosion were screened out, and the effect of soil erosion on the soil quality was studied, all of which may lay the foundation for soil quality evaluation, management, and the evaluation of soil erosion environmental effect. Therefore, the effect of soil erosion including rainfall event, one-year erosion (gully erosion) and long-term erosion on soil quality was studied. The study was conducted in the cultivated slope land at three different temporal scales including rainfall event, gully erosion and long-term erosion. Sixteen erosion soil physical and chemical indicators were screened out and determined in this study. The effect of soil erosion on soil quality was analyzed and performed quantitatively by correlation analysis method and principal component analysis method. The main results were summarized as follows:
1. It was different for erosion soil quality responding to the various erosion scales like rainfall event, one-year erosion and long-term erosion. Compared with the chemical properties, soil physical indicator would change more obvious under the condition of rainfall event. Moreover, the available nutrient content was easier to change than the total nutrient content. The soil pH changed non-significantly. When the gully erosion happened, There was a difference among the effect of gully erosion on soil quality single-factors in the cultivated slope land, gully erosion would harden the soil and increase the pH value, while the change of soil water-stable aggregate and nutrient content showed an obvious hierarchy with increment of gully erosion depth. The change law seemed like the letter “W” shape. After long-term rain-erosion, the soil quality index changed non-significantly. Both the variance coefficients of single soil quality factors and the soil quality index were small. In the soil nutrient indicators, the available nutrient content was easier to change than the total nutrient content. In the soil available nutrient indicators, the variance coefficient is soil available P > soil available nitrogen > soil available potassium. In the soil total nutrient indicators, the variance coefficient is total N > total P. The variance coefficient of soil organic matter was small and the variance coefficient of soil pH was smallest. 2. There was a close correlation between soil physical and chemical properties under various erosion conditions. When the rainfall event happened, there was a well relationship between soil organic matter and soil clay content, mean weighted diameter, soil available potassium, soil aggregate content (r>0.65). However, there was not an obvious relationship between soil organic matter and soil bulk density, soil pH under both low and high soil quality ground. After gully erosion, there is a significant positive correlation between soil organic matter and soil surface area, small aggregate (0.5~0.25 mm), soil clay content. there was a positive but not significant correlation between soil organic matter and small aggregate (1~0.5 mm). After the long-term erosion, there was a most significant positive correlation between soil organic matter and soil total nitrogen and significant correlation between soil organic matter and soil available nitrogen, soil available P, soil quality index. Besides, a well relationship would be found between soil available P and soil total nitrogen, soil available nitrogen, soil quality index (r >0.6). 3. Soil fine particle loss may be the main reason that led to the degradation of soil physical property and the loss of soil nutrient. The effect of gully erosion on soil quality index could be preferably fitted by the power function curve of y = 0.8668x - 0.142 (R2 = 0.877, y- Soil quality index, x- Gully erosion depth). The soil quality index showed a three-decreased progress with the increment of soil gully erosion depth compared with the control soil. The soil quality indexes under the condition of low erosion intensity (<5 cm), mid erosion intensity (5~30 cm) and high intensity (30~50 cm) reduced by 10.6%, 27.9% and 36.5%, respectively. The soil quality index under the erosion depth of 5 cm and 30 cm reduced significantly, respectively.
4. The key soil indicators were different at the three temporal scales (rainfall erosion event, gully erosion and long-term erosion). When the rainfall event happened, soil organic matter content and soil clay content could reflect the erosion soil quality evolution. The 4 soil quality indicators including soil organic matter, soil surface area, soil aggregate content and soil bulk density screened out by principal component analysis method and discriminant analysis method were regarded as the most sensitive and simplified indicators for evaluating soil quality influenced by gully erosion in the cultivated slope land on the Loess Plateau. After the long-term erosion, there was a close relationship between soil quality index and soil organic matter content, soil available P, soil available N. these indicators could be regarded as the key soil indictors under the condition of long-term rain-erosion. 5. There was a difference for soil properties after soil erosion at various temporal scales under the condition of different soil quality ground. When the rainfall event happened, compared with the soil quality index of the control, the soil quality index changed non-significant after soil erosion under the condition of low soil quality ground while it was significant when it happened under the high soil quality ground. The soil quality index reduced 7.2% and 11.9%, respectively. It showed that the high quality soil was easier to degrade than the low quality soil after the same soil erosion process. After gully erosion, the soil organic matter loss would be more serious in the high quality soil ground when the soil erosion intensity was low (0~10 cm). when the erosion depth was 10~30 cm, the soil organic matter loss would follow the law of Mid > Low > High. At the erosion depth of 30~50 cm, the soil organic matter loss showed a stable trend under the three soil quality ground (Low (SOM< 5 g/kg), Mid (5≤SOM<10 g/kg) and High (10 g/kg ≤SOM) soil quality ground). Key words: Cultivated slope land; Soil erosion; Soil quality assessment; Temporal scales; Loess Plateau