Getting to the Root of the Problem - Assessing Crop Water Uptake Using Geophysics

Abstract:

Increasing demands on the agricultural industry to produce higher crop yields and provide sustainable agriculture solutions under changing climate and land use is, in part, constrained by the tools available to explore crop-soil-water interactions at the field scale. Traditional measurements of soil moisture offer information about local scale processes, or are resource intensive for investigation at the large scale. As in many other areas of hydrology, geophysical techniques are emerging as potentially valuable methods for large scale investigations, although the full potential of these methods is yet to be realised. We report here on a field-based experimental study in which electrical resistivity tomography and multi-coil electromagnetic induction methods were used to monitor changes in soil electrical conductivity over the growing season of winter wheat (Triticum aestivum L.). Changes in electrical conductivity was used as a proxy for changes in soil water content in an attempt to reveal different characteristics of soil water uptake by 23 different lines of wheat. The study was performed in a randomised block experiment using replicate plots for each wheat line. Neutron probe data and penetrometer measurements collected during the study permit a comparison with direct estimates of changes in soil water and changes in soil strength, respectively. The results of the geophysical surveys appear consistent with these independent measurements. Additional constraints in interpretation due to the effect of soil cracking are also explored. It appears that electrical conductivity is potentially useful as an indicator of changes to soil water in such agricultural environments. Resolving subtle differences between different lines of wheat may be challenging and limit the value of these methods in breeding programs. However, the ability to monitor changes in soil water status over large areas with vehicle-mounted geophysical instrumentation remains a major potential advantage of such methods.