This study focuses on the reliable parametrization of the full Soil Water Retention Curve (SWRC) from saturation to oven-dryness using high resolution but limited range measured water retention data by the Hydraulic Property Analyzer (HYPROP) system. We studied the performance of five unimodal water retention models including the Brooks and Corey model (BC model), the Fredlund and Xing model (FX model), the Kosugi model (K model), the van Genuchten constrained model with four free parameters (VG model), and the van Genuchten unconstrained model with five free parameters (VGm model). In addition, eleven alternative expressions including Peters–Durner–Iden (PDI), bimodal, and bimodal-PDI variants of the original models were evaluated. We used a data set consisting of 94 soil samples from Turkey and the United States with high-resolution measured data (a total of 9264 measured water retention data pairs) mainly via the HYPROP system and supplemented for some samples with measured dry-end data using the WP4C instrument. Among unimodal expressions, the FX and the K models with the Mean Absolute Error (MAE) values equal to 0.005 cm3 cm−3 and 0.015 cm3 cm−3 have the highest and the lowest accuracy, respectively. Overall, the alternative variants provided a better fit than the unimodal expressions. The unimodal models, except for the FX model, fail to provide reliable dry-end estimations using HYPROP data (average MAE: 0.041 cm3 cm−3, average r: 0.52). Our results suggested that only models that account for the zero water content at the oven dryness and properly shift from the middle range to dry-end (i.e., the FX model and PDI variants) can adequately represent the full SWRC using typical data obtained via the HYPROP system.
The accumulation of excess soluble salts in the root zone of arid and semiarid irrigated soils is a widespread problem that seriously affects crop productivity. The cultivated soil profile under irrigation is the main media in which the salinization occurs. In this study, the effects of different irrigation water salinity and leaching ratio on soil profile salt mass balance changes were investigated in alfalfa (Medicago sativa L.) cultivated PVC lysimeters (115 cm in height and 40 cm diameter). Three irrigation water salinity (S 1 , S 2 , and S 3 , 0.25, 1.5 and 3.0 dS m -1 , respectively) and four leaching ratios, LF, (10%, 20%, 35% and 50% more water than ET) levels were used in a fully randomized factorial design experiment with three replications. The total salt mass balance was calculated from the subtraction of total salt mass concentration supplied with irrigation water and total salt mass concentration washed out with the drainage water. When the salinity content of irrigation water increased leaching of SO 4 2and Claccumulation in the soil increased. Increase in the leaching ratio (LF) caused increase in the leaching of Clthrough the soil profile. The major cations, Ca 2+ , Mg 2+ , and Na + , in the soil were also evaluated for their total mass concentrations regarding salinity content of irrigation water and LF. Ca 2+ concentration in the soil profile increased with salinity level and the leaching ratio, whereas Mg 2+ and Na + mass concentrations decreased considerably. This is due to the high Ca 2+ adsorption in the soil than that of Na + . The effect of LF on the ion mass accumulation or leaching varied depending on the ion type.
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