Soil Moisture Sampling and Decision Frameworks for Agriculture.

Sampling of soil moisture involves a temporal and spatial component. The spatial component can be further expanded into a vertical and horizontal array of observations that are required to understand the dynamics of processes occurring with the soil profile. The decision frameworks for agriculture require both the temporal and spatial components be accurately characterized and, in many cases, linked with estimations of the amount and time of recharge in the soil water profile. In irrigated systems, this becomes more predictable; however, in rainfed environments and areas with supplemental irrigation, the estimation of recharge amounts increases the uncertainty in any decision framework. Accurate soil moisture sampling requires techniques with the ability to quantify the soil water content at any point and be robust enough to provide this accuracy throughout a growing season of a crop. The techniques for measuring soil water range from gravimetric, neutron probes, capacitance or conductance probes, to microwave systems. All of these techniques have their limitations and their strengths. The continued development of probes that can be installed into the soil profile provide methods of continually measuring the soil water content with depth and are economic to allow for spatial assessments across fields. Microwave systems can provide a quantification of the spatial variation at the surface and when linked with thermal infrared could provide an assessment of the spatial variation across a field or a landscape induced by differences in soil water availability. The decision framework for agriculture depends upon the decision being made; i.e., the framework for irrigation management is different than decisions of whether there is sufficient soil water to effectively utilize any applied nitrogen to a crop. The continued development of decision support tools will reveal the most appropriate spatial and temporal scales required for different agricultural decisions.