Changes in SOC and nutrients under intensive tillage in two types of slope landscapes

The net effect of tillage erosion on soil properties would be associated with the spatial variation in soil constituents, and therefore plays an important role in ecological agriculture. We conducted a consecutive tillage by hoeing 15 times during a period with no rainfall in the two slope landscapes (a linear slope and complex slope) of the Yangtze Three Gorges reservoir areas, to examine the relationship between soil erosion rates and the variations in soil chemical properties and compare the effects of soil redistribution on SOC and nutrients between the linear and complex slopes. After the simulated tillage, notable changes in ¹³⁷Cs inventories of the soil occurred in the summit and toeslope positions on the linear slope, while there were significant changes in ¹³⁷Cs inventories at convex and concave positions on the complex slope. Soil profile disappeared at the summit slope boundary, with the exposure area of 16.0% and 7.6% of the experimental plot, respectively, for the linear and complex slopes due to no soil replacement. Soil organic C and nutrients were completely depleted with the disappearance of soil profiles at soil eroding zones, whereas a remarkable increase in SOC, total N and available nutrient concentrations of the post-tillage surface soil and a decrease in total nutrient concentrations (P and K) were found at depositional zones on the linear slope. For the complex slope, however, changes in SOC and nutrient concentrations of the post-tillage surface soil exhibited a pattern different from that on the linear slope, which showed a remarkable decrease in SOC and total nutrient concentrations but a slight increase in available nutrient concentrations after tillage in the toeslope position. Due to the gradual increase in soil depth from top to bottom of the slope, SOC and nutrient inventories in the soil profiles were significantly correlated with soil redistribution rates on both the linear and complex slopes. Tillage causes remarkable changes of soil chemical properties in the surface soil layer and soil profile, and increases SOC and nutrient inventories for the soil profile downslope in steeply sloping landscapes.