System Dynamic Model Of 1-Dimensional Unsaturated Water And Solute Transport For Predicting Salinity Stress In Crops

There is a complex non-linear system dynamic between the water and salt transport in the unsaturated vadose zone where the salt transport and accumulation affect the water fluxes and vice versa. In addition, factors such as precipitation, transpiration, water infiltration and solute transport in the unsaturated zone of subsurface soil further complicate the processes involved. We have developed a system dynamics model for simulating the one-dimensional unsaturated water and solute transport along with root water uptake in the vadose zone. The model uses finite difference method for solving Richard\u27s equation with a sink term for water transport and root water uptake; and advection-diffusion equation for solute transport. The stock-flows for water and solute transport is discretized into different soil layers from top until it leaches out into an end stock. The root water uptake, water and solute transport are interconnected using physically based formulations and empirical assumptions. The model predicts the impact on root water uptake due to water and salinity stress as a function of matric and osmotic potential. The model\u27s results were similar to the results from HYDRUS showing that the model is capable of predicting salinity and matric stress in crops and could be a useful tool for analyzing various geographical soil and crops. El Paso county is located in the Chihuahua desert in Texas in an arid region with prolonged drought conditions. In order to evaluate the salt accumulation in the soil layers, we revisited a severe drought period in the history of El Paso with record low rainfall from 1947 to 1956. The system dynamic model was used to simulate water infiltration, solute transport and root water uptake for cotton and pecan crops with five different combinations of irrigation water. These waters had a common source as rainfall and two other sources of river and groundwater bringing an influx of solute into the system. Irrigation water with 100% groundwater predicted the highest salt concentration in the root zone in the range of 10 mg/cm3 (15.6 dS/m) whereas 100% river water predicted the lowest in the range of 2 mg/cm3 (3 dS/m). The assessment of root water uptake for the first and last ten years of simulation period showed a reduction in crop yield for pecan and cotton by 44% and 88%, respectively