Modelling Water in Crops and Plant Ecosystems

Abstract

A water submodel is described that is specifically designed for use with plant growth simulators that represent internal plant substrates and variable shoot:root partitioning. The model calculates water flow from soil to root, root to shoot, and shoot to the atmosphere, for a closed-canopy situation. As presented here, the model has three state variables: the masses of water in the soil, root and shoot, and represents the processes of evapotranspiration, rainfall interception and evaporation from the canopy, and drainage. The Penman –Monteith equation is used for crop transpiration. The fluxes of water from soil to root, and root to shoot, are driven by water potential difference. Tissue water potential and its components are calculated from tissue water content and other plant variables and parameters. The model is able to simulate osmoregulation and describes a variable relationship between tissue water potential, its components and relative water content, depending on growth conditions. The model has elsewhere been integrated with two plant ecosystem models: for grassland and forest. The specific implementation and simulations given are for the Hurley pasture model (Thornley and Verberne, 1989), a temperate grass vegetative growth model. The model gives reasonable predictions for diurnal changes in water potential, drying-down behaviour and other quantities within the scope of the model.