HR: 1340h
AN: H53E-0525    [Abstracts]
TI: Modeling compensated root water and solute uptake
AU: * Simunek, J
EM: Jiri.Simunek@ucr.edu
AF: Dept. of Environmental Sciences, University of California Riverside, Riverside, CA 92521 United States
AU: Hopmans, J W
EM: jwhopmans@ucdavis.edu
AF: Dept. Land, Air and Water Resources, University of California Davis, Davis, CA 95616 United States
AU: Jarvis, N
EM: Nick.Jarvis@mv.slu.se
AF: Dept. of Soil Sciences, Swedish Univ. of Agricultural Sciences, Uppsala, 750 07 Sweden
AB: Numerical models based on the Richards equation usually simulate root water uptake as the product of the potential transpiration, a root distribution function, and water and solute stress response functions. Root water uptake is then multiplied by local concentrations to get the passive root solute uptake. Numerical models usually do not compensate for a reduction of the potential uptake due to osmotic and pressure head stress in one part of the root zone by increased root water or solute uptake in other parts. Here we present a new compensated root water and solute uptake model that we implemented in HYDRUS models. Following Jarvis [1989], we use a critical value of the water stress index w, a so-called the root adaptability factor, which represents a threshold value above which root water uptake reduced in stressed parts of the root zone is fully compensated by increased uptake from other parts. Using a critical value of the water stress index w, the water uptake compensation is proportional to the water stress response function. Water uptake increase (compensation) is maximum from parts of the root zone where the root water uptake is optimal (i.e., not reduced), equal to zero from parts of the root zone where the pressure head is below the wilting point or above the anaerobiosis point, and proportional to the water stress response in the pressure head intervals in between. Root solute uptake, calculated subsequently at each time step, is divided into an active and passive solute uptake. Passive solute uptake is obtained by multiplying the compensated root water uptake by the maximum concentration Cmax that can be taken up by plant roots. The Cmax parameter allows the control of the passive root water uptake. All solute dissolved in water is taken up by plant roots when Cmax is large, while no solute is taken up when Cmax is equal to zero. Only the active uptake is present in the latter case. The active solute uptake is then obtained from the difference between the plan nutrient demand and the passive solute uptake. The actual local active solute uptake rates are calculated invoking the Michaelis-Menten kinetics. Similar compensation procedure as used for the root water uptake is implemented also for the active solute uptake rate, i.e., invoking solute stress index s. This model implies that if the root water uptake is reduced, thus decreasing the passive solute uptake, the active solute uptake increases proportionally. Additional flexibility can be added to the model by reducing the potential solute (nutrient) demand proportionally to the reduction of the water uptake.
DE: 1842 Irrigation
DE: 1852 Plant uptake
DE: 1866 Soil moisture
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: Fall Meeting 2005