Mechanical sowing alters slope-scale spatial variability of saturated hydraulic conductivity in the black soil region of Northeast China

Saturated hydraulic conductivity (Ks) and its spatial variability are essential for the simulation of water and solute transport in the vadose zone. Mechanical operations have been increasingly employed in agricultural systems during recent decades to improve crop establishment, but their impact on Ks spatial variability has rarely been evaluated. The objectives were to characterize the slope-scale variability of Ks and to identify the primary controls dominating Ks distributions before and after mechanical sowing. Along a 900 m slope transect in the black soil region of Northeast China, soil samples were collected in an interval of 20 m, and Ks, bulk density (BD), particle-size distribution, wet-aggregate stability (WAS), soil organic carbon content (SOC) and land surface roughness (SR) were investigated before and after mechanical sowing in the spring. The results show that sowing significantly decreased Ks along the transect (p < 0.01). Partly due to the strong comparisons among three different sections with respect to soil erosion, i.e., original, erosive and deposited sections, large Ks spatial variability was detected both before and after sowing. According to the semivariogram analysis, nevertheless, sowing decreased the semivariances of Ks overall and altered its spatial structure, i.e., from an exponential semivariogram possessing a sill of 0.72 mm² min⁻² and exhibiting a moderate spatial dependency before sowing to a pure nugget effect value of 0.27 mm² min⁻² corresponding to random distribution after sowing. Using the state-space approach, BD, CLAY and SR were identified as the main factors regulating Ks spatial distributions, whether before or after sowing. These findings demonstrate the remarkable impact of mechanical sowing on Ks and its spatial variability, and hold important implications for hydrological modeling and agricultural management in the black soil region of Northeast China.