SEASONAL TRENDS IN FURROW IRRIGATION EROSION IN SOUTHERN IDAHO

A study was conducted to measure the seasonal irrigation furrow erosio n pattern in the absence of cultivation and a growing crop. This erosi on pattern was compared to those of previous measured plot experiments for different years in the presence of cultivation and a growing crop . Erosion for su,garbeets, corn and beans was low early in the season and increased to a maximum during the same 3-week period, from 24 June to 10 July over several years. Erosion decreased as the irrigation se ason progressed after the erosion peak. The erosion pattern from the u ncultivated, non-cropped plots resembled the pattern from previous stu dies on cropped soil with the maximum erosion occurring about the same time of season. The pattern trends differed only after peak erosion. For the cropped plots, there was a sudden erosion decline after peak e rosion, followed by a continual gradual decrease. In contrast, for the uncultivated, non-cropped plots, there was a sudden erosion decline a fter peak erosion, followed by a gradual increase in erosion. Although the seasonal erosion pattern cannot be completely explained, it is im portant to report it because of the implication for erosion modeling. Sediment loss rates measured from these soils in southern Idaho in lat e June or early July would significantly overestimate seasonal erosion , whereas sediment loss rates measured in May or early June or after m id-July would underestimate seasonal erosion. These results show that researchers cannot rely upon a one-time measurement for model validati on if attempting to predict irrigation furrow erosion over an entire i rrigating season.