Two‐dimensional spatial variation of soil physical properties in two tillage systems

Abstract Soil physical properties are known to be variable as a result of tillage in both space and time; however, small‐scale variations (<1 m) related to tillage are poorly characterized. In this study, morphological descriptions of soil structures created by tillage under conventional (CT) and conservation or mulch (MT) tillage are related to bulk density (ρ b ) and hydraulic conductivity ( K ) measurements to determine causality and to predict the effects of tillage practices on these properties. Mouldboard ploughing in CT tended to create marked spatial heterogeneity in soil physical properties within the tilled layer, a finding well expressed in the results from morphological description. This method was much less applicable to MT due to a more homogeneous spatial distribution of soil physical properties. Under both tillage systems, rows had higher bulk density values and lower hydraulic conductivity than inter‐rows. The global geometric mean of the saturated hydraulic conductivity was higher and more variable under CT than under MT (66 vs. 41 mm/h). Under each tillage system, zones with a high capacity to conduct water were identified (inter‐furrows under CT with a mean K S of 720 mm/h, and soil zones with earthworm burrows and cracks in MT with a mean K S of 400 mm/h). In the untilled layer, higher K values were measured under MT than under CT (40 vs. 22 mm/h). The contrast in K between the tilled and the untilled layers was very limited for MT compared to CT where mouldboard ploughing resulted in marked contrast between both layers. The assessment of this small‐scale variability in soil physical properties aids our understanding of water and solute movement through topsoil layers.