Soil-water characteristic curves and their estimated parameters as affected by tillage intensity

Tillage alters soil structure and pore size distribution, consequently affecting the shape of the soil-water retention curve (SWRC) and related hydraulic parameters in the top layer of soil. This work compares the effect of no-tillage (NT) and conventional tillage (CT) practices on SWRCs 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 0-15 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 evaporative method. Measured soil-water retention curve data were modeled 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 practices. Averaged across 4 years and two depths, the SWRC parameters α, n, and θ_s were significantly greater under CT than under NT, however, θ_r was not affected by tillage. The higher α, n, and θ_s values in CT were likely associated with greater soil loosening and disturbance induced by CT operations, thereby forming greater macroporosity and pore volume. Regardless of the tillage method, SWRCs enable growers to select farming and irrigation management practices that improve water use efficiency, sustain crop productivity and maintain environmental quality.