Abstract: Increasing P loss from soils caused by runoff has contributed to contamination of surface waters in the Great Plains. Knowledge of P forms in runoff is necessary to develop appropriate land management practices and reduce the impact of P on water resources. A 2-year study was conducted on the Roca watershed, located in Lancaster County, Nebraska. This watershed is part of the Great Salt Creek watershed, which is considered a representative of watersheds in the Northern Great Plains. The objectives were to apply the Natural Resources Conservation Service technique to (i) estimate P loss from soils by runoff, (ii) determine P forms in the runoff, and (iii) estimate P loading and impact on water quality in Salt Creek. The annual loss of P by runoff was estimated at 17.7 tons for 2009 and 22.1 tons for 2010. These losses could be considered as the annual P loadings into Salt Creek. The predicted average dissolved P concentration in the runoff was 532 and 464 μg/L during 2009 and 2010, respectively. Most of the P measured in Salt Creek during the 2-year study was in the dissolved reactive (DRP) form (79%), and the remaining P was associated with suspended sediment, mainly in unreactive form (UP). The observed average DRP in stream water was 462 and 454 μg/L for 2009 and 2010, respectively. For each year, the predicted DRP was within 1 S.D. of the observed value. The data supported the applicability of the Natural Resources Conservation Service technique to estimate soil P losses and the impact on surface waters in the Great Plains.
1U.S. Department of Agriculture/Natural Resources Conservation Service, Lincoln, NE. Dr. Moustafa A. Elrashidi is corresponding author.
2Virginia Polytechnic Institute & State University, Blacksburg, VA.
Address for correspondence: Dr. Moustafa A. Elrashidi, U.S. Department of Agriculture/Natural Resources Conservation Service, National Soil Survey Center, 100 Centennial Mall North, Lincoln, NE 68508; E-mail: Moustafa.firstname.lastname@example.org
Financial Disclosures/Conflicts of Interest: None reported.
Received May 30, 2012.
Accepted for publication October 3, 2012.