Spatial and Temporal Variability of Soil Water Content in Leveled Fields

Abstract

Water scarcity threatens the sustainability of crop production and environmental stewardship in several regions of the globe. Precision irrigation appears as a promising way to sustain productivity while using lower amounts of water. While precision irrigation is at its infancy stage, farmers and crop practitioners often doubt the existence of spatial variability of soil water content in leveled fields (slope of 1% or lower in a single plane gradient). The objectives of this study were to quantify the spatial and temporal variability of soil water content in leveled fields. Neutron probe readings were acquired at five depths over a whole crop growing season at two sites. A total of 41 and 31 locations from north eastern Colorado were monitored. Moran's I and semivariograms were used to study the data. Results showed that up to 87% of measured soil water content locations across leveled fields can be mis-represented by the field's mean soil water content. In general, the spatial range of dependency was shorter for soil water content near the surface than with depth, indicating that more sample points may be required to characterize near-surface soil water contents than at deeper depths. Temporal dependency of soil water content was 50 d or more at or greater than depths of 45 cm. In general, the spatial and temporal variability of soil water content observed in this study was conducive to the implementation of water management zones because it was variable in space with long spatial range, yet with long temporal dependency.