Wetting patterns for wheel and nonwheel irrigated furrows
Bromide (Br–) masses recovered by extensive sampling of very fine sandy loam soil to a depth of 1.5 m defined the pattern of soil water movement from irrigated furrows. Wheel traffic occurred in alternate furrows. Bromide was applied in the irrigation water in three-wheel and three-nonwheel furrows. All border furrows and furrows between treated furrows were irrigated with untreated water. Small amounts of the bromide tracer moved laterally and vertically throughout the soil profile surrounding wheel furrows. Bromide mass in samples taken directly beneath wheel furrows was as high as 35.5 mg kg–1 of soil, while bromide mass in samples taken beneath adjacent ridges seldom exceeded 8.89 mg kg–1 of soil. These data suggest that water movement from wheel furrows was generally downward, probably because compaction reduced the infiltration rate and also because much of the flow was non-Darcian. The location and amount of bromide surrounding nonwheel furrows at the lower end of the field were similar to wheel furrows, probably because of the relatively short infiltration opportunity times. Only at the upper end of nonwheel furrows, where an average depth of 260 mm of water was infiltrated, was bromide found in quantities large enough to infer substantial lateral movement.