Modelling corn rooting patterns and their effects on water uptake and nitrate leaching

Water and nitrogen absorption by corn (Zea mays L.) are partly determined by the region in the soil containing roots and, as a result, rooting patterns could change water availability and leaching of nitrates. A two-dimensional model of corn root growth was developed and linked to a two-dimensional model for water, heat acid solute transport in soil. The model was calibrated with root distribution and soil environment data obtained in a Mollisol at Lamberton, MN. Changing the root growth parameters allowed the model to be used to compare water uptake and NO3 leaching between a shallow, dense root system and a deep, sparse root system. For the rainfall conditions used in model validation, the model predicted a small amount of water absorption from lower in the soil profile with the deep, sparse root system compared with the shallow root system, but that most of the water for transpiration would come from shallow depths directly below the plant. Nitrate leaching was almost identical for both root systems. However, the model predicted reduced downward movement of N when plant uptake of water occurred than with no plant water uptake. The bulk volume of soil explored by the root system may be more important for determining water availability and possible plant water stress during dry periods than for decreasing fertilizer or pesticide leaching. The model should be useful for other examinations of water and chemical movement in the soil by including the effects of the plant in the system. The model also allows at least a preliminary examination of soil management effects on water and nutrient availability.