Factors controlling saturated hydraulic conductivity along a typical black soil slope

Saturated hydraulic conductivity ( K s) is controlled by a suite of soil processes operating at various scales. Little is known about the spatial variability of Ks along a slope and how it is changed through the planting operation process and the specific scales at which the controlling factors function. The objective was to characterize the scale-dependent relationships between K s and various soil processes and thereby to identify the primary controlling factors of K s. On a typical slope transect of 900 m in the black soil region of Northeast China, K s and six soil properties of bulk density (BD), wet-aggregate stability (WAS), surface roughness (SR), soil organic carbon content, sand and clay contents were investigated in an interval of 20 m before and after mechanical sowing in the spring. Statistical correlation analysis, its combination with noise-assisted multivariate empirical mode decomposition (NA-MEMD) and wavelet coherence were employed to examine the interactions between K s and each factor at different spatial scales. The BD was admittedly the dominant factor controlling K s, followed by WAS and SR before and after sowing, respectively. The statistical correlation analysis only detected the significant interactions between K s and BD, whereas the essential influence of WAS and SR were revealed upon frequency component decompositions by NA-MEMD and biwavelet coherency. Applying multiple wavelet coherence, BD was believed adequate in explaining K s variability before sowing, whereas the combination of BD and SR was suggested in the case after sowing. These findings hold important implications for precise K s estimations in the black soil region of Northeast China as well as other similar regions, and also demonstrate the effectiveness of NA-MEMD and wavelet coherence in untangling complex scale-dependent relationships among soil processes. ● K s and six factors were measured before and after sowing along a slope in NE China. ● Scale-dependent relationships were observed between K s and each soil factor. ● BD was admittedly the primary factor, followed by WAS before and SR after sowing. ● Multiple wavelet coherence believed BD was adequate for K s estimation before sowing. ● The combination of BD and SR was selected to explain K s variability after sowing.