TRANSIENT 3-DIMENSIONAL MODELING OF SOIL-WATER AND SOLUTE TRANSPORT WITH SIMULTANEOUS ROOT-GROWTH, ROOT WATER AND NUTRIENT-UPTAKE

A three-dimensional solute transport model was developed and linked to a three-dimensional transient model for soil water flow and root grow th. The simulation domain is discretized into a grid of finite element s by which the soil physical properties are spatially distributed. Sol ute transport modeling includes passive and active nutrient uptake by roots as well as zero- and first-order source/sink terms. Root water u ptake modeling accounts for matric and osmotic potential effects on wa ter and passive nutrient uptake. Root age effects on root water and nu trient uptake activity have been included, as well as the influence of nutrient deficiency and ion toxicity on root growth. Examples illustr ate simulations with different levels of model complexity, depending o n the amount of information available to the user. At the simplest lev el, root growth is simulated as a function of mechanical soil strength only. Application of the intermediate level with root water and nutri ent uptake simulates the influence of timing and amount of NO3 applica tion on leaching. The most comprehensive level includes simulation of root and shoot growth as influenced by soil water and nutrient status, temperature, and dynamic allocation of assimilate to root and shoot.