SPATIAL AND SEASONAL-VARIATION OF FURROW INFILTRATION

Infiltration was measured with a newly developed flow-through infiltrometer at 20-27 sites in a 21 ha (52-acre) cotton field in the northern region of the San Joaquin Valley of California. The results were comparable with infiltration measured with a neutron probe. The infiltrometer allowed water to flow through the infiltrometer when a rate test was not being conducted. Furthermore, the water level and quality inside the infiltrometer was the same as the water flowing past in the remainder of the furrow. Variability contributed by soil infiltration characteristics and intake opportunity time was quantified for preirrigation as well as for three postplant irrigations. The mean and variability of infiltration were greater for the preplant than the postplant irrigations, and soil variability contributed more to total infiltration variability than did the variability in intake opportunity time. Because the infiltration pattern was temporally correlated between postplant irrigations, representative sites rather than a complete field interrogation could be used to estimate mean and variability of infiltration.