Anisotropy of subsoil pore characteristics and hydraulic conductivity as affected by compaction and cover crop treatments

Abstract

The natural and cover crop (CC)‐induced anisotropy of subsoil pore characteristics is important in assessments of soil compaction but, until recently, has received limited attention. This study aims to quantify the anisotropy of soil pore characteristics and hydraulic conductivity in subsoils subjected to compaction and CC treatments in a split‐plot field experiment on temperate sandy loam soils. The main factor was ±compaction and the split‐plot factor was ±CC with fodder radish (Raphanus sativus L.). The compacted plots were heavily trafficked for 4 yr (2010–2013). After 4 yr under CC (2013–2016), core samples were collected at 0.3 m. The samples were taken vertically and horizontally to quantify the anisotropy of air‐filled porosity (εa) and air permeability (ka), saturated hydraulic conductivity (ksat), and bulk density (ρb). The results showed isotropic behavior for ρb and εa and significant anisotropic behavior (p < .05) for ka, pore geometry index (PO1) (ka/εa), ratio of non‐Darcian to Darcian ka (R‐ratio), and ksat. For parameters with significant anisotropy, higher values occurred vertically than horizontally for all compaction –CC combinations, except for R‐ratio. This indicates that pre‐existing vertical continuous pores dominated the pore system in the control subsoil. A nonsignificant trend of higher values of ka, PO1, and ksat in the +CC than in the compacted –CC plots suggest that CC could contribute to the formation of vertical biopores. Including an autumn CC in rotation with a summer cereal crop for a longer period may significantly affect the anisotropy of the soil pore and hydraulic properties.

X-ray Microtomography Analysis of Integrated Crop-Livestock Production Impact on Soil Pore Architecture

“…The degree of anisotropy (Figure 5c) reflects the arrangement of soil pores in different directions [58,59]. Our study observed the highest 𝐷𝐴 values for NT, although minor differences (p>0.05) were observed between treatments.…”