Tillage effects on soil hydraulic parameters estimated by Brooks-Corey function in clay loam and sandy loam soils

Authors: Jabro, Jalal; Stevens, William; Iversen, William; Sainju, Upendra; Allen, Brett; Rana Dangi, Sadikshya

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2025
Publication Date: 9/29/2035
Citation: Jabro, J.D., Stevens, W.B., Iversen, W.M., Sainju, U.M., Allen, B.L., Rana Dangi, S. 2035. Tillage effects on soil hydraulic parameters estimated by Brooks-Corey function in clay loam and sandy loam soils. Agronomy Journal. 15(10). Article 2325. https://doi.org/10.3390/agronomy15102325.
DOI: https://doi.org/10.3390/agronomy15102325

Interpretive Summary: Tillage operations and soil disturbance have a significant and direct impact on soil physical and hydraulic properties, including soil-water retention curve, pore-size distribution, large and small pore spaces, and total porosity. ARS scientists at the Northern Plains Agriculture Research Laboratory in Sidney Montana conducted a study to evaluate the effect of no-tillage and conventional tillage practices on the estimated parameters of Brooks-Corey’s model for soil-water retention curves at 0-15 cm and 15-30 cm depths in sugarbeet and corn planting rows in clay loam and sandy loam soils, respectively. Soil-water retention curve describes the relationship between volumetric water content and matric suction forces and is affected by soil particle size distribution (soil texture), soil structure, organic matter, tillage, and soil compaction. When soil in the field is holding maximum water against gravity, a point referred to as field capacity. Soil water is depleted over time to the point that plants are unable to pull it away from the soil and the plants wilt. The point where this happens is referred to as the permanent wilting point. The amount of water content between these two soil water levels is known as plant-available water. It is easy for plants to uptake this form of water from the soil. Clayey soils usually have a higher total porosity and can hold more water than sandy soils at a given soil water potential force. Changes in soil-water retention due to the tillage depends on the size and portion of pores. Untilled soils generally hold more water than tilled soils under a given soil water potential force. Understanding these soil-water relationships is important for agronomic, soil, irrigation, and environmental and hydrological studies. Regardless of the type of tillage and soil, these relationships can empower producers and researchers to accurately estimate available water for plants, allowing them to effectively plan irrigation events. The relationships provide good information about pore-size distribution in the soil that governs water infiltration into the soil surface and water storage in the soil profile. Long-term effects of no-tillage practices adaptation could improve soil structure compared to tilled soils due to an increase in plant residues and organic matter levels in the surface soil layer over time.

Technical Abstract: Tillage practices can significantly impact soil structure, pore-size distribution and connectivity, consequently affecting the shape of the soil-water retention curve (SWRC) and its related estimated hydraulic parameters in the top layer of soil. This study investigated the effect of no-tillage (NT) and conventional tillage (CT) practices on SWRCs, and their soil hydraulic parameters estimated by the Brooks-Corey (BC) function at 0-15 and 15-30 cm depths within sugarbeet and corn planting rows in clay loam and sandy loam soils, respectively. Soil-water retention curves were measured using the evaporative method (HYPROP). Measured SWRC results were modeled for both untilled and tilled soils using the BC function for each depth in both soils. In clay loam, results indicated that all soil parameters of the BC function, water contents at 330 ('330) and 15000 ('15000) hPa, and plant available soil water content (AW) were not significantly affected by type of tillage at either soil depth. The lack of difference in results between NT and CT may be due to considerable soil disturbance, primarily by the harvest process of sugrabeet roots. However, in sandy loam, results indicated that differences occurred in SWRC’s estimated parameters between the NT and CT practices. Averaged across 4 years and two soil depths, the pore-size distribution index (') and saturated water content ('s) were significantly larger under CT than under NT due to greater soil loosening and disturbance caused by multiple passes of the CT process, thereby developing more soil macroporosity. However, the '330 and AW were significantly larger in NT than in CT due to reduced soil disturbance and improved soil structure under NT compared to CT practices. Whether untilled or tilled soils, measurements of SWRC are important for determining better irrigation management practices, enabling producers to optimize crop productivity, while saving water and sustaining water quality.