Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 16, 2005
Publication Date: April 13, 2006
Citation: Bjorneberg, D.L., Westermann, D.T., Aase, J.K., Clemmens, A.J., Strelkoff, T. 2006. Sediment and phosphorus transport in irrigation furrows. Journal of Environmental Quality. 35:786-794. Interpretive Summary: Sediment and phosphorus in runoff from furrow irrigated fields can impair water quality in streams, lakes and rivers. Sediment and phosphorus transported in irrigation furrows was measured during six irrigations over five years. Flow rate and sediment and phosphorus concentrations were measured at four, equally-spaced locations within each furrow to identify changes as water flowed down a furrow. Furrow flow rate decreased with distance down the furrow as water infiltrated. This reduced the amount of sediment that the furrow flow could carry and often caused sediment to be deposited on the lower end of the field. Most of the phosphorus transported with furrow flow was associated with sediment on these tilled, fallow fields. The concentration of phosphorus that was dissolved in flowing water decreased with time at a given location, and increased with distance down the furrow at a given time. Factors that affected dissolved phosphorus concentration included time that the water was in contact with soil and suspended sediment, suspended sediment concentration, and furrow soil phosphorus concentration. This study demonstrated that sediment and phosphorus transport in irrigation furrows involves many interacting processes occurring during the relatively short time (10 to 30 minutes) that water flows down the field in a furrow.
Technical Abstract: Sediment and phosphorus (P) in runoff from furrow irrigated fields can impair water quality in streams, lakes and rivers. We conducted a series of whole field studies to better understand the factors that affect phosphorus transport during furrow irrigation. Irrigation furrows provide a controlled channel or rill in which changes in sediment and P concentrations can be measured without interference from raindrops or additional sheet flow that occurs during natural or simulated rain. Six irrigations were conducted on freshly tilled, fallow fields that varied from 110 to 180-m long, with 0.007 to 0.012% slopes. The soil on all fields was Portneuf silt loam (coarse-silty, mixed superactive, mesic Durinodic Xeric Haplocalcids). Flow rate, sediment concentration and phosphorus concentrations were monitored at four, equally spaced locations in each furrow. Flow rate decreased with distance down the furrow as water infiltrated. Sediment concentration varied with distance and time with no set pattern. Total P concentrations were directly related to sediment concentrations (coefficient of determination was 0.75) because typically >90% of the P was associated with particulates. Dissolved reactive P (DRP) concentrations decreased with time but tended to increase with distance down the furrow. DRP concentration correlated better with sediment concentration than extractable furrow soil P concentration. However, DRP concentration was not usually affected by changes in suspended sediment concentration later in the irrigation (>2 h). Accurately predicting erosion is essential to predicting P losses associated with sediment. Predicting sediment detachment/deposition also appears to be important for predicting DRP loss from tilled fields where erosion occurs.