Abstract:
This study aims to investigate the effects of ridge tillage on physical crust pore characteristics and soil infiltration in the black soil region of Northeast China. Research objects were taken as the crusted soil under non-ridging, as well as the structural crust and sedimentary crust soil in two ridge directions (contour and downslope ridge tillage). Sampling and in-situ experiments were conducted in May and September 2023, respectively. A systematic analysis was conducted to determine the variations in soil micro-pores during crust development using CT scanning technology and
in-situ infiltration experiments. The results showed that ridge tillage caused the differentiation of crust characteristics between ridges and furrows, according to the relationship between crust characteristics and infiltration. Contour ridge tillage promoted the development of sedimentary crust, with the increasing proportion of water-stable aggregates in the furrow. Longitudinal ridge tillage also intensified the sorting effect of runoff on soil particles. The porosity of the crust layer increased with the time under contour ridge tillage, where the pore size approached gradually. The porosity showed an increasing trend from the crust surface to the subsoil layer. The soil pores of the crust shared a double closure under longitudinal ridge tillage. The number of throats in the sedimentary crust decreased significantly to form the more isolated pores. The more concentrated runoff in the furrows drastically reduced the sediment particles. As such, the sedimentary crust was thinner than that under contour ridge tillage. The large pore of the crust layer was better preserved under non-ridging conditions. The average infiltration rate of crust soil was ranked in the descending order of the non-ridging (0.58 mm/min) > contour ridge tillage (0.15 mm/min) > longitudinal ridge tillage (0.11 mm/min). Ridge tillage regulated the soil infiltration to form the different types of crusts. The soil water-holding capacity rapidly increased with soil saturation after the crust formation. The water retention time was prolonged under the high proportion of capillary pores in crusted soil, leading to a significant decline in the infiltration of crusted soil. The initial infiltration rate was controlled by the bulk density of the surface crust and subsoil, while the steady infiltration rate was primarily dominated by the pore structure, subject to the crust thickness and water-stable aggregates. Different types of crusts with ridge tillage were the main influencing factors on the infiltration rate. The pore networks were more developed under contour ridge tillage. Correspondingly, soil porosity improved the soil infiltration. The initial and steady infiltration rates of crusted soil were effectively predicted using bulk density and saturated water holding capacity of the subsoil, while the WSA> 0.25 and the thickness of the crust layer. The findings can also provide important theoretical support for the optimal ridge tillage to reduce soil erosion.