Nondimensional Relationship for Root Water Uptake in Crops

Root water uptake is often modeled as a sink term in the Richards equation to account for evapotranspiration losses. The sink term is assumed to be a power law function in the nonlinear root uptake model (O-R model) to account for the decrease in root density and water uptake with depth. In order to extend the O-R model to other crops without requiring detailed and time-consuming experiments, two important dimensionless numbers (specific transpiration, Ts, and specific root water uptake, T*) are identified based on readily available plant parameters. Data for determining the relationship between these numbers are obtained by minimizing the deviations between the field-observed moisture depletions of 28 crops reported in literature and the numerically simulated soil moisture depletions. Field experiments on three Indian cropsmaize, Indian mustard, and wheatare used for validation of the proposed empirical relationship. This relationship shows promise for use in the O-R model for root water uptake for a variety of crops.