Influence of soil texture on soil moisture and soil water potential dynamics

Accurate assessment of soil moisture is essential for effective irrigation management, particularly in soils with contrasting textures. Soil water availability is governed by the relationship between volumetric soil water content (θv) and soil water potential (Ψ), which varies with soil texture. The objective of this study was to develop empirical θv-Ψ relationships for twelve USDA soil textural classes and to evaluate the influence of soil texture on soil moisture and soil water potential dynamics. An outdoor experiment was conducted using twelve soil textural classes, with Decagon EC-5 and Watermark 200SS sensors installed in soil-filled plastic containers. Sensor measurements were compared with the gravimetric method as the reference, and best-fit models were determined using regression analysis. Fine-textured soils (clay, silty clay, and clay loam) exhibited higher θv and showed more gradual changes in Ψ, whereas coarse-textured soils (sand and loamy sand) retained less water and showed rapid declines in Ψ with decreasing θv. Average threshold values of approximately 40 and 44 kPa were identified for the gravimetric-Watermark and Decagon EC-5-Watermark relationships, respectively. Strong relationships were observed between θv measured using the Decagon EC-5 sensor and gravimetrically determined θv, with coefficients of determination ranging from R2 = 0.987 to 0.997 and RMSE values between 0.29% and 4.94%. Polynomial models provided the best fit for most soil textures, including sand (R2 = 0.994), sandy clay (R2 = 0.992), silty clay (R2 = 0.997), and clay loam (R2 = 0.995). Ψ showed greater variability across soil textures, with R2 values ranging from 0.745 in sand to 0.970 in clay and silty clay and RMSE values ranging from 2.39% in loamy sand to 5.33% in clay. These results demonstrated that θv and Ψ varied with soil texture, emphasizing the need for soil-specific interpretation because irrigation thresholds cannot be universally applied across contrasting soil textures.