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Assessment of Phosphorus Retention in Irrigation Laterals

Ippolito, J.A. and Nelson, N.O. (2013) Assessment of Phosphorus Retention in Irrigation Laterals. Journal of Soil and Water Conservation. 68(6):450-459. November 2013.

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Irrigation laterals transport irrigation return flow, including water, sediment, and dissolved nutrients, such as phosphorus (P), back to surface water bodies. Phosphorus transformations during transport can affect both P bioavailability and the best management practices selected to minimize P inputs to waters of the United States. The objective of this study was to determine P retention in three irrigation laterals. Soluble reactive P (SRP) concentrations in lateral waters were increased from 0.08 to 0.25 mg L -1 (0.08 to 0.25 ppm) by constantly injecting a phosphate (PO4) solution for 2.5 hours. Bromide (Br) was used as a conservative tracer to determine dilution effects. Water was sampled at 10-minute intervals, beginning 30 minutes prior to injection and 120 minutes following injection, at one upstream location and various downstream locations to approximately 1,550 m (~1 mi) from injection sites. When at steady state, SRP concentrations only decreased by 5% over the lengths studied, equating to P uptake lengths of over 18 km (11.2 mi), which was one to two orders of magnitude greater than natural streams; the linear SRP uptake rate was 0.011 mg L -1 km -1 (0.018 ppm mi -1 ). Longer P uptake lengths and lower uptake rates in irrigation laterals, as compared to natural streams, may be due to the elevated sediment equilibrium P concentration, greater water velocities, and removal of vegetation causing a reduction in frictional resistance. Reducing water velocities should optimize irrigation lateral conditions to reduce uptake length and maximize P uptake.

Item Type: Article
NWISRL Publication Number: 1477
Subjects: Irrigation > Furrow irrigation > Drainage water (see Percolation water)
Water > Water quality > Nutrients
Depositing User: Users 6 not found.
Date Deposited: 18 Nov 2013 17:26
Last Modified: 18 Nov 2013 17:26
Item ID: 1513