Dynamics of Soil Water and Nitrate in the Root-Zone Under Cover Crop and Winter Fallow Using a Combination of Soil Monitoring and Modelling.

The distribution of both water and nutrients in the root-zone can be highly non-uniform. The shape of the wetted soil volume under micro-irrigation and the spatial distribution of soil water, and nitrate concentrations are dependent on many factors, including soil layering, hydraulic properties, emitter discharge rates, spacing, and their placement (above or below the soil surface), irrigation quantity and frequency, crop water uptake rates, etc. In general, root development in micro-irrigated field is constrained to the soil volume wetted by the irrigation water, with root length density decreasing with depth, whereas plants can quickly adapt their spatial pattern of water and nutrient uptake in response to irrigation water application distribution. Also, roots can adjust their uptake patterns, thereby compensating for local stress conditions by enhanced or preferential uptake in other regions of the rooting zone with less stressful conditions. A better understanding of the interactions of irrigation method, soil type, crop root distribution, and uptake patterns and rates of water and nutrients or solutes will provide improved means for proper and efficient microirrigation water management practices. A combination of soil water and nutrient monitoring methods and modeling techniques is needed for better understanding of the complexities in the root-zone of agricultural fields. We present experimental data on soil moisture, water potential, and nitrate concentration combined with modeling of unsaturated water flow and solute transport to evaluate and optimize irrigation and fertility management practices for multiple locations, crop types, and irrigation systems.