Evaluating the Splintex model for estimating the soil water retention curve for a wide range of soils

The soil water retention curve (SWRC) describes how much water can be retained and is available for plants in soil under different matric potentials. SWRC plays an essential role in the modeling of soil hydraulic processes and can be estimated with pedotransfer functions (PTFs). Splintex 2.0 is a PTF model developed with a userfriendly computer interface that can estimate soil hydraulic functions' parameters. As opposed to common PTFs that need to be calibrated using empirical data, Splintex 2.0 was based on a semi mechanistic model that translates particle-size distribution data into solid mass fractions and pore-size distribution. The objective in this work was to widely test the performance of Splintex 2.0 against the performance of its previous version (Splintex 1.0) using a database of 1355 samples from various countries. This large number of samples allowed a detailed quantification of the univariate and bivariate probability distributions of the estimated parameters in different hydrogeology, climate, and soil types. The accuracy of Splintex 2.0 was examined by means of linear correlation analysis (r) for random errors and of mean error (ME), mean absolute error (MAE), and root mean square error (RMSE) for systematic errors. The Splintex 2.0 model overcame the estimation's discrepancy of SWRCs from its previous version and performed similarly with two other published PTF models. In particular, Splintex 2.0 performed as well as these published PTFs in estimating water content at field capacity over a wide range of soil types. In summary, because of its mechanistic nature, Splintex 2.0 can be an alternative model for estimating SWRC and field capacity in new areas where there is a lack of calibration data.

Automated summary

The Splintex 2.0 model, based on a semi mechanistic model, demonstrated accurate estimation of soil hydraulic functions' parameters and performed well in estimating water content and field capacity, showing potential as an alternative model for areas lacking calibration data. Comparisons with previous version and other PTF models indicated the reliability and effectiveness of Splintex 2.0 across a wide range of soil types.