WETTING PATTERNS FOR WHEEL AND NONWHEEL IRRIGATED FURROWS

Bromide (Br-) masses recovered by extensive sampling of very fine sand y loam soil to a depth of 1.5 m defined the pattern of soil water move ment from irrigated furrows. Wheel traffic occurred in alternate furro ws. Bromide was applied in the irrigation water in three-wheel and thr ee-nonwheel furrows. All border furrows and furrows between treated fu rrows were irrigated with untreated water Small amounts of the bromide a tracer moved laterally and vertically throughout the soil profile s urrounding wheel furrows. Bromide mass in samples taken directly benea th 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 furr ows was generally downward, probably because compaction reduced the in filtration rate and also because much of the flow was non-Darcian. The location and amount of bromide surrounding nonwheel furrows at the lo wer end of the field were similar to wheel furrows, probably because o f the relatively short infiltration opportunity times. Only at the upp er 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.