Estimating soil hydraulic parameters in fine-textured soils using HYDRUS-1D coupled with PEST
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Date
2024-08-23
Authors
Kaur, Ishmeet
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Abstract
Frequent flooding and drought events lead to moisture stress in crops, which leads to poor crop yield and quality. Thus, water management strategies are needed to create a conducive environment for plant growth and performance. An effective strategy requires a long-term understanding of soil moisture dynamics regulated by local soil hydraulic properties and hydrologic factors. This study focused on estimating these soil hydraulic parameters using HYDRUS-1D coupled with PEST (external calibration software) and exploring the non-unique nature of the solution for four growing seasons (2016 –2019). One hundred initial guesses of parameter sets were generated for each year for model calibration. The volumetric soil water contents determined at the site within the 0 - 10 cm, 10 - 30 cm, 30 - 70 cm, and 70 - 130 cm layers over the growing seasons were used to calibrate and validate the models. The statistical parameters used for the evaluation of models were NashSutcliff efficiency (NSE) (0 - 1), Percent bias (PBIAS) (±10%), Ratio of Root Mean Square Error to standard deviation (RSR) (< 0.7) and R2 (> 0.5). The results showed that PEST was useful in establishing the non-linearity and non-unique nature of the solution, which established that different parameter sets could result in similar performance and, therefore, ascertained the use of a more rigorous approach (maximum likelihood) based on different parameter sets to improve the reliability of the results. The model performance was satisfactory for the simulation of soil water content in 2016, 2017, and 2019 using the calibrated parameter sets. Poor model performance was observed for the 2018 validation period, which showed how the physical manipulation of soil (tillage), physiological stage of the crop, and soil response to weather (shrink-swell) could alter the soil hydraulic properties to a great extent within a season. The results also demonstrated that the saturated hydraulic conductivity varied over the years to about ten times for the topsoil (plough horizon) but was almost constant for deeper soil layers.
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Keywords
HYDRUS, PEST, inverse modelling, soil hydraulic parameters