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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVED WATER RESOURCES MANAGEMENT FOR IRRIGATED AGRICULTURE IN THE PACIFIC NORTHWEST

Location: Northwest Irrigation and Soils Research

Title: Assessment of Phosphorus Retention in Irrigation Laterals

Authors
item IPPOLITO, JAMES
item Nelson, N -

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 28, 2013
Publication Date: November 6, 2013
Repository URL: http://handle.nal.usda.gov/10113/58012
Citation: Ippolito, J.A., Nelson, N.O. 2013. Assessment of phosphorus retention in irrigation laterals. Journal of Soil and Water Conservation. 68(6):450-459.

Interpretive Summary: The objective of this study was to determine phosphorus retention in three irrigation laterals. Soluble reactive phosphorus concentrations in lateral waters were increased by constantly injecting a phosphate solution. When at steady state, soluble reactive phosphorus concentrations only decreased by 5 percent over the lengths studied, equating to phosphorus uptake lengths of over 11 kilometers, or one to two orders of magnitude greater than phosphorus uptake lengths typical of natural streams. Reducing water velocities and increasing water depth, with a concomitant increase in fine sediment size, should optimize irrigation lateral conditions for reduced uptake length and maximum phosphorus uptake

Technical Abstract: Irrigation laterals transport irrigation return flow, including water, sediment, and nutrients, back to surface water bodies. Phosphorus transformations during transport can affect both phosphorus bioavailability and the best management practices selected to minimize phosphorus inputs to waters of the USA. The objective of this study was to determine phosphorus retention in three irrigation laterals. Soluble reactive phosphorus concentrations in lateral waters were increased from 0.08 mg/L to 0.25 mg/L by constantly injecting a phosphate solution for 2.5 hours. Bromide was used as a conservative tracer to determine dilution effects. Beginning 30 minutes prior to injection and 120 minutes following injection, water was sampled at 10 minute intervals at one upstream location and various downstream locations to approximately 1550 meters from injection sites. When at steady state, soluble reactive phosphorus concentrations only decreased by 5 percent over the lengths studied, equating to phosphorus uptake lengths of over 11 kilometers, or one to two orders of magnitude greater than phosphorus uptake lengths typical of natural streams; the linear soluble reactive phosphorus uptake rate was 1.1 'g/m/s. Longer irrigation lateral phosphorus uptake lengths and lower uptake rates, as compared to natural streams, may be due to the elevated lateral sediment equilibrium phosphorus concentration, greater water velocities, and removal of lateral vegetation causing a reduction in frictional resistance. Reducing water velocities and increasing water depth, with a concomitant increase in fine sediment size, should optimize irrigation lateral conditions for reduced uptake length and maximum phosphorus uptake.

Last Modified: 9/10/2014
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