Natural and management-induced dynamics of hydraulic conductivity along a cover-cropped field slope

Improving structure-related hydraulic properties by sustainable soil management is essential to avoid runoff and soil erosion. In order to analyse the management impact of cover cropping on an agricultural field slope, near-saturated hydraulic conductivity (kh) was measured by a tension infiltrometer at three pressure heads (h). The effect of four cover crops (phacelia, vetch, rye, mustard) and a fallow treatment was evaluated by a mixed model analysis of variance and compared to the influence of spatial trends along the slope and seasonal changes over two winters. Substantial over-winter changes were found with a significant increase in kh and a reduction in the flow-weighted mean pore radius (λm). Texture-structure-related trends along the slope resulted in a higher kh at lower pressure heads at the summit with higher fractions of coarse particles, while kh tended to be highest at the toeslope towards saturation. The higher λm at the toeslope for a given conductivity suggests a higher contribution to the infiltration flux of inter-aggregate pores. Soil cover management accounted for a maximum of 9.7% of the total variability in kh, with a decreasing impact towards the unsaturated range, while strong interactions between the soil cover treatments and environmental factors were found. The flux potential in the range of measured h was lowest for those cover crops with most intense growth, which also showed a smaller λm at a given kh. This suggested partial pore clogging by the cover crop roots. Cover crops in both years showed a higher over-winter increase than fallow which was shown to be mainly a result of enhanced pore formation. The results revealed that the potential impacts of cover crops for managing soil infiltrability are largely governed by the natural temporal variability of structure-related hydraulic properties in the field.