PHOSPHORUS LOADING IN FURROW IRRIGATION TAILWATER

Authors: Clemmens, Albert; Westermann, Dale; Strelkoff, Theodor; Bjorneberg, David - Dave

Submitted to: Proceedings of the World Water and Resources Congress
Publication Type: Proceedings
Publication Acceptance Date: 5/30/2004
Publication Date: 7/1/2004
Citation: Clemmens, A.J., Westermann, D.T., Strelkoff, T., Bjorneberg, D.L. Phosphorus loading in furrow irrigation tailwater. In: Proceedings of the World Water and Environmental Resources Congress. June 27-July 1, 2004, Salt Lake City, Utah. 2004 CDROM.

Interpretive Summary: Phosphorus (P) transport to streams from furrow irrigation tailwater is a significant water quality issue in the Pacific Northwest. When critical concentrations of P are exceeded in surface waters, excessive algae and other aquatic vegetation growth can lead to eutrophication. Agriculture has been designated as the primary source of P entering inland streams, lakes and water impoundments by EPA. Under this NRI funded research project, we have collected field data to document the phosphorus loads that occur under furrow irrigation conditions in Kimberly, Idaho. Most of the phosphorus transported off the field is associated with the eroded sediments. We have developed an erosion detachment, transport and deposition component for the surface irrigation model SRFR. Laboratory batch studies were conducted to determine the amount of phosphorus released when soil is entrained in water, as occurs under furrow erosion. Flume studies were conducted to determine the amount of phosphorus released from the soil surface under non-erosive conditions. A phosphorus transport component is being added to SRFR to model the transport of P with eroded soil and the desorption of P into the irrigation water from both the eroded soil and the soil surface. This paper presents a status report on this modeling-field verification effort on P transport from furrow-irrigated fields. The final results of this research should be of use to actions agencies, such as NRCS, irrigation farmers, EPA, and environmental groups.

Technical Abstract: Phosphorus (P) transport to streams from furrow irrigation tailwater is a significant water quality issue in the Pacific Northwest. Under this NRI funded research project, we have collected field data to document phosphorus loads that occur under furrow irrigation conditions in Kimberly, Idaho. Since the majority of phosphorus transported off the field is associated with eroded sediments, we have developed an erosion detachment, transport and deposition component for the surface irrigation model SRFR. This model has the ability to track particle-size distributions in the furrow flow. A modification to the Laursen transport formula was required for small particle (silt and clay) sizes. Laboratory batch studies were conducted to determine the amount of phosphorus released when soil is entrained in water, as occurs under furrow erosion. There appears to be influences from both sediment:water mass ratios and P concentration in the water, as well as soil P indices. Flume studies were conducted to determine the amount of phosphorus released from the soil surface under non-erosive conditions. Preliminary results suggest that soil P release is influenced by the flow regime (turbulent or laminar) at the interface between the soil and the water in the furrow. Turbulent flow results in more P released, and potentially desorbed and diffused from deeper soil layers. A phosphorus transport component is being added to SRFR to model the transport of P with eroded soil and the desorption of P into the irrigation water from both the eroded soil and the soil surface. Several new modeling approaches are being explored. This paper presents a status report on this modeling - field verification effort on P transport from furrow-irrigated fields.