Spatial Features, Scaling and Simulation in Semi-Arid Agricultural Terrain

Spatial patterns of soils and vegetation in undulating terrain must be quantified to improve process understanding and differential management on agricultural lands. Spatial variance and patterns of crop yield are pronounced in rain-fed agricultural fields of eastern Colorado, where past and present transport of sediment by wind and water affect soil properties that vary with the terrain. Coupled processes of overland flow, infiltration, and multidimensional soil-water flow and storage affect the space-time scaling behavior of measured soil hydraulic properties, soil-water content, soil nutrient status, crop development and ultimate grain yield. Such spatial process interactions give rise to nested scales of variability. Improved process understanding and simulations are needed to identify when and where observed complexity cannot be explained by vertical processes. For example, soil variability alone may not explain observed patterns of soil water. To test this hypothesis, hourly soil-water contents have been measured with electrical capacitance sensors at different landscape positions and depths. Numerical simulations of this system, including dynamic plant growth with water and nutrient uptake, will be presented under both fallow and cropped conditions to explore combined soil, terrain and agronomic effects on water and nutrient transport. We assert that such agronomic systems comprise the “cream of the critical zone” of the western USA needed to sustain life under various climatic and economic pressures.