High-Resolution Field-Scale Mapping of Plant-Available Water Using Penetrometer-Mounted Visnir Spectroscopy.

Water utilization and stress are critical drivers of yield in all cropping systems. While irrigation and rainfall ultimately limit the total amount of water in any system, within field yield variability often arises from variability in soil hydraulic properties rather than variability of water inputs (i.e. irrigation and rainfall).  One critical soil hydraulic property that influenced yield is plant-available water (PAW).  Knowledge of the field-scale spatial distribution of PAW is needed for precision management of both irrigated and dry-land systems however; current soil maps are often too coarse to provide meaningful field-scale information.  Development of the high-resolution digital soil maps needed for precision management of PAW is limited by the high cost of collecting soils data.  Recent developments in proximal soil sensing such as penetrometer-mounted visible near-infrared spectroscopy (VisNIR) have allowed for rapid, low-cost collection of soils data.  With penetrometer-mounted VisNIR, in situ measurements of soil properties can be gathered in rapid succession because there is no need for collection, preparation, and analysis of soil samples. By coupling in situ VisNIR with existing pedotransfer functions, we can predict and map PAW at the field scale.  These field-scale maps could be used to inform precision management such as delineating management zones for variable planting rates or site-specific irrigation regimes.