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

Authors: Jabro, Jalal - Jay; Stevens, William - Bart

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2022
Publication Date: 2/9/2022
Citation: Jabro, J.D., Stevens, W.B. 2022. Soil-water characteristic curves and their estimated hydraulic parameters in no-tilled and conventionally tilled soils. Soil & Tillage Research. 219. Article 105342. https://doi.org/10.1016/j.still.2022.105342.
DOI: https://doi.org/10.1016/j.still.2022.105342

Interpretive Summary: Tillage management practices have significant effects on soil physical and hydraulic properties. ARS scientists at the Northern Plains Agriculture Research Laboratory in Sidney Montana conducted a long-term study to evaluate the effect of no-tillage and intensive tillage practices on a soil’s soil water retention curve and hydraulic properties. The curve describes the relationship between changes in volumetric water content and how tightly water is held by the soil. As the amount of water in the soil decreases the water that remains is held more and more tightly. Plant roots ‘pull’ water away from the soil and the more tightly water is held by the soil the more difficult it is for plant roots to absorb it. When soil in a field is holding all the water it can—a point referred to as field capacity—it is easy for plants to absorb the water. Eventually soil water is depleted to the point that plants are no longer able to pull it away from the soil and the plant wilts and dies. The point where this happens is referred to as the permanent wilting point. The amount of water between these two benchmarks is known as plant-available water. Knowledge of these values as determined from a soil-water characteristic curve is essential for many plant, soil, irrigation, hydrological, and environmental studies and applications. Whether soils are tilled or not tilled, these soil-water-related relationships can empower farmers and researchers to accurately estimate field capacity, permanent wilting point and available water capacity for plants, allowing them to effectively schedule irrigation events. Results from this study conclusively demonstrated that these benchmarks are extremely useful for irrigation management and scheduling that ensures efficient use of water, optimize yield production levels, and minimize chemical leaching. The direct impact of this research is significant for farmers and researchers who can accurately determine the amount and timing of irrigation water to apply to their crops in order to maintain yield while avoiding groundwater contamination with chemicals.

Technical Abstract: 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 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 HYPROP 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 management practices. Averaged across 4 years and two depths, the SWRC parameters a, n, and 's were significantly greater under CT than under NT, however, 'r was not affected by tillage. The higher a, n, and 's 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.