Soil water retention and hydraulic conductivity dynamics following tillage

Soil bulk density (rho(b)) may be purposely reduced in agricultural fields using tillage to improve hydraulic properties. However, tillage alters the soil structure, resulting in unstable soils. As the soil stabilizes, rho(b) increases over time. While this is known, studies on soil hydraulic properties in tilled soils, including comparisons between tilled and non-tilled soils, commonly assume a rigid soil structure. This study presents changes in soil water retention and saturated hydraulic conductivity (K-sat) as rho(b) increased dynamically with time following tillage at a loam-textured field site. Over the summer of 2015, soil cores were collected at several depths below the surface following precipitation events. Soil water retention curves and K-sat were determined using pressure cells and the constant head method, respectively. Tillage reduced rho(b) to 0.94g cm(-3). Changes in rho(b) increased with depth, reaching a rho(b) of 1.11 g cm(-3) in the 0-5 cm layer, and a rho(b) of 1.42 g cm(-3) at the deepest tilled layer. Soil water retention curves were markedly steeper for samples with higher rho(b), indicating an overall increase in water retained at a soil matric potential (Psi) of similar to 33 kPa. Evaluation of two modeling approaches for water retention as a function rho(b) indicated that changes in water retention with increases in rho(b) could be reasonably estimated if a matching point was used. No clear relationship between K-sat and rho(b) was obvious for rho(b) < 1.06 cm(3) cm(-3), but for rho(b) > 1.06 cm(3) cm(-3), K-sat decreased markedly (order of magnitude) as rho(b) increased. Hydraulic properties varied strongly depending on time since tillage and soil depth, and results have implications for models of tilled soils, as well as for studies comparing tilled and non-tilled soils.