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Assessment of phosphorus retention in irrigation laterals

Permanent URL:
http://handle.nal.usda.gov/10113/58012
File:
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Abstract:
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.
Author(s):
J. A. Ippolito , N. O. Nelson
Subject(s):
best management practices , drainage water , irrigation rates , irrigation systems , irrigation water , phosphorus , streams , surface water , velocity , water flow , United States
Source:
Journal of soil and water conservation 2013 v.68 no.6
Language:
English
Year:
2013
Collection:
Journal Articles, USDA Authors, Peer-Reviewed
Rights:
Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.