Spatial and Temporal Variability of Soil Moisture Content in Leveled Fields.

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, several farmers and crop practitioners question the existence of spatial variability of soil moisture content in leveled fields and thus the potential benefits of variable rate irrigation in such fields. The objectives of this study were to quantify the spatial variability of soil moisture content in leveled fields (slope below 3%), and to describe the temporal variability of soil moisture content. Neutron probe readings were acquired at 5 depths over the whole crop growing season at two sites. A total of 41 and 31 locations at Site 1 and Site 2 respectively were monitored in a systematic unaligned pattern. Spatial statistics were used to study the spatial autocorrelation (Moran’s I) and the range of autocorrelation (using semi-variograms) in volumetric soil moisture content. Data were also classified in irrigation management classes (above field capacity (FC), between FC and maximum allowable depletion (MAD) and below MAD) to compare the field average to every locations of the field. Temporal variability was studied using correlograms. Results showed that there was spatial autocorrelation in majority of the cases and that Moran’s I and coefficients of variation were correlated with depths of reading. Spatial range was from 42 m up to 334 m depending on the depth, site and average soil moisture. Correlograms showed that soil moisture content was correlated over time (Pearson’s r above 0.5) and that temporal autocorrelation increased with depth. These results indicated that the spatial structure and the temporal stability of soil moisture content are conducive to spatial management of water in leveled crop fields.