Soil-water characteristic curves and their estimated hydraulic parameters in no-tilled and conventionally tilled soils

Tillage loosens soil, reduces bulk density, alters soil structure and pore size distribution, consequently affecting the shape of the soil-water retention curve (SWRC) and related hydraulic properties and parameters in the top layer of soil. Knowledge of SWRC and hydraulic properties are needed for many soil, agronomic, irrigation, hydrological and environmental studies. This work compares the effect of no-tillage (NT) and conventional tillage (CT) practices on SWRCs and their estimated parameters at 0–15 and 15–30 cm soil depths based on soil samples collected in 2014, 2015, 2016, and 2017. Undisturbed soil cores were extracted using stainless steel cylinders (8 cm in diameter and 5 cm in height) from 0 to 15 cm and 15–30 cm depths in planted corn rows. Soil core sampling was replicated five times in a randomized block design. Soil cores were saturated prior to measurement by the capillarity method and SWRC were measured using the HYPROP evaporative method. Measured soil-water retention curve data were fitted for no-tilled and tilled soils using the van Genuchten (vG) equation for each depth. Results indicated that differences existed in SWRC properties and estimated parameters of vG equation between the two tillage management practices. Averaged across 4 years and two depths, the SWRC parameters α, n, and θs were significantly greater under CT than under NT, however, θr was not affected by tillage. The higher α, n, and θs values in CT were likely associated with greater soil loosening and disturbance induced by CT operations, thereby forming greater macroporosity and pore volume that, in turn, caused a decrease in bulk density in CT compared to NT. Regardless of the tillage method, SWRCs enable growers and researchers to select farming and irrigation management practices that improve water use efficiency, sustain crop productivity and maintain environmental quality.