Spatial and Temporal Variability of Water Content and Infiltration on a Flood Irrigated Field

Abstract

ABSTRACT The variability of water contents and cumulative infiltration was measured on a flood irrigated field over four irrigations. Changes in water storage at 44 locations were calculated from the differences between the water contents measured before and after each irrigation with a neutron probe. Infiltration was measured with 42 single-ring infiltrometers located on a single transect down the field. The variability in calculated water storage was very consistent from irrigation to irrigation, with specific locations consistently measuring either high or low. Rankings of the locations from low to high water storage showed little variation between irrigations. Variograms showed that water storage was spatially correlated to distances of 30 m and that the spatial structure was identical from irrigation to irrigation. Changes in water storage due to irrigation were more variable but still displayed a consistency over time. The variogram for the change in water storage had a large nugget value and ranges near 20 and 90 m. Infiltration equation parameters measured with the infiltrometers were extremely variable over time as indicated by low correlation coefficients. Depths of cumulative infiltration, however, were much more consistent over time with extreme values being consistently measured at the same locations. The spatial correlation of the cumulative infiltration depths extended to distances less than 3.8 m. Calculations of the irrigation uniformity from the infiltrometer measurements were less than uniformities based on measured water contents. The discrepancies between these two measures are due, in part, to difficulties in measuring infiltration parameters with ring infiltrometers that are representative of infiltration for the border as a whole and to the effects of lateral flow and redistribution on water content measurements.