Evaluation of water flux prediction with heat-pulse technique in saturated soils

Heat-pulse technique (HPT) has shown promise for predicting soil water flux (J(w)). This study evaluated the accuracy of HPT in predicting Jw in packed saturated columns of quartz, sand, silt loam, and sandy clay loam. J(w) was predicted using the maximum dimensionless temperature differences (MDTD), ratio of downstream to upstream temperature increases (T-d/T-u), and an improved T-d/T-u method. Results indicated that J(w) predictions had a good linear relationship with measurements (R-2 > 0.93). The HPT underestimated J(w) to varying degrees, and the underestimations increased as J(w) increased and soil texture became fine. The T-d/T-u method outperformed the MDTD and the improved T-d/T-u because of its higher accuracy, fewer parameters, and simpler calculations. The MDTD exhibited the poorest performance. In coarse-textured soil materials (e.g. quartz and sand), Jw predictions by the T-d/T-u method were most accurate, and even with high J(w) (up to 72.4 mu m s(-1)), relative errors still remained within 9.8%. However, in fine-textured soil materials, J(w) was underestimated significantly by 16.9% in silt loam and by 23.3% in sandy clay loam. The lower J(w) limits were 1.0, 2.3, 2.4, and 4.0 mu m s(-1) for quartz, sand, silt loam, and sandy clay loam, respectively (P > 0.05)