Sensitivity analysis of Hydrus software to input data in simulating water movement and root uptake of grass as a reference plant

Abstract

IntroductionUnderstanding the movement of water in the soil and the process of root water uptake is critical. Numerical simulation is an effective solution for optimizing water management in the field. Accurate prediction of water movement in the soil and root water uptake, to create optimal moisture conditions in the root zone, is important for better plant performance. Investigating the phenomenon of water absorption by roots in hydrological and plant models requires a quantitative description of water absorption by plant roots. Accuracy of model simulation in predicting soil water transfer and root absorption, as temporal and spatial variables, is the most important criterion in agricultural issues.Materials and MethodsThe water movement in the soil and root water uptake were simultaneously simulated using HYDRUS-3D software. For this purpose, the grass plant was cultivated in three lysimeters with the same soil texture. The grass plant was irrigated every three days at 10 am. The soil water content of the depths of 5, 15, 25, 40, 60, and 80 cm was measured every day at 10 am and 6 pm. The volume of water drained from the lysimeters was measured every day. The measurements were done over a period of 81-day. Soil’s physical properties were measured in the laboratory.Results and DiscussionThe results showed that in all simulations, the minimum and maximum relative errors were obtained at 0.79 and 35.1%, respectively. The cumulative measured volume of drainage water in the whole period is 162.75 liters and the cumulative volume of simulated drainage water in the whole period is 133.79 liters. The relative error between these two values ​​is equal to 5.28%. Rainfall amounts have a significant effect on estimating the volume of simulated drainage water and its difference from the measured volume of drainage water. With the increase of initial moisture and soil hydraulic conductivity, the relative error between the measured and estimated drainage water data increases, and with the increase of saturated moisture and residual moisture in the soil, the relative error decreases. The values of root water uptake (Minimum 0.5 and maximum 3.5 liters in one irrigation interval), showed that in the third stage of growth, root absorption has the maximum value and by comparing the actual and potential root absorption, which have a low difference, no stress has been applied to the plant.ConclusionThe change in the input parameters causes a change in the estimated volume of drained water at the beginning of the period. When the initial moisture and residual soil moisture are considered as 0.3 and 0.15325, respectively, the relative error between the measured and estimated drainage water data is the lowest. The root water uptake values were also estimated using the model. According to the values of actual and potential root water uptake, in the whole period, which has very small differences, no stress has been applied to the grass plant and sufficient water has been provided to the plant.

Keywords

• characteristic curve
• hydrus-3d
• root uptake
• soil
• water