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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #293426

Title: Long-term agroecosystem research in the Central Mississippi River Basin: dissolved nitrogen and phosphorus transport in a high-runoff-potential watershed

Author
item Lerch, Robert
item Baffaut, Claire
item Kitchen, Newell
item Sadler, Edward

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2014
Publication Date: 1/8/2015
Publication URL: http://handle.nal.usda.gov/10113/60624
Citation: Lerch, R.N., Baffaut, C., Kitchen, N.R., Sadler, E.J. 2015. Long-term agroecosystem research in the Central Mississippi River Basin: dissolved nitrogen and phosphorus transport in a high-runoff-potential watershed. Journal of Environmental Quality. 44:44-57. DOI: 10.2134/jeq2014.02.0059.

Interpretive Summary: Long-term nutrient monitoring data from agricultural watersheds are needed to determine if efforts to reduce nitrogen (N) and phosphorus (P) transport from crop and pasture land have been effective. Results from a 19-year (1992-2010) study of nutrients in stream water of Goodwater Creek Experimental Watershed (GCEW), a predominantly agricultural watershed located in northeastern Missouri, were summarized and trends assessed. Data were also compiled to document concurrent changes in land use and N and P fertilizer inputs to the watershed from 1992 to 2010. Annual concentrations and loads (mass) for nitrate were greater than those of ammonium and orthophosphate, and concentrations of all three nutrient forms consistently exceeded those of reference streams within the region and levels known to impair aquatic ecosystems. However, annual nitrate and ammonium concentrations significantly decreased over the study, and annual nitrate loads decreased by 43 percent in the last 9 years of the study compared to the first 10 years. Seasonal loads showed that the 1st and 2nd quarters of the calendar year accounted for 61 to 83 percent of annual loads. The seasonal pattern of orthophosphate concentrations suggested that sediment-bound P was a key source to the stream. Factors such as precipitation, land use, and fertilizer inputs were critical to nutrient transport. For example, winter wheat production drastically decreased during the study from 1227 to 111 hectares, resulting in significant decreases in 1st quarter concentrations of all three nutrients, demonstrating the much greater transport risk associated with fall applied fertilizer. Additional improvements in fertilizer management for corn, particularly incorporation of broadcast N fertilizer in the spring, also appeared to contribute to decreases in nitrate over the study. These results clearly demonstrated the water quality benefits associated with shifting fertilizer application from fall to spring. Improvements in fertilizer management to reduce runoff losses of N and P to streams economically benefits producers through improved fertilizer use efficiency and increased grain yields, and benefits the general public by improved stream water quality and reduced costs for drinking water treatment.

Technical Abstract: Long-term nutrient monitoring data from agricultural watersheds are needed to determine if efforts to reduce nutrient transport from crop and pasture land have been effective. The objectives of this study were to: 1) summarize dissolved ammonium-N (NH4-N), nitrate-N (NO3-N), and orthophosphate-P (PO4-P) flow-weighted concentrations (FWCs) and unit area loads (UALs) in a high runoff potential watershed, Goodwater Creek Experimental Watershed (GCEW), from 1992 to 2010; and 2) assess time trends and relationships between land use and N and P fertilizer inputs to nutrient transport. Annual FWCs and UALs for NO3-N were the highest of the three nutrient species, and nutrient FWCs consistently exceeded those of reference streams within the ecoregion and levels known to impair aquatic ecosystems. However, annual NO3-N and NH4-N FWCs significantly decreased over the study, and annual NO3-N UALs decreased by 43 percent in the last 9 years of the study compared to the first 10 years. The seasonal pattern of PO4-P FWCs suggested that desorption of sediment-bound orthophosphate was a key source to the stream. Seasonal loads showed that the 1st and 2nd quarters of the year accounted for 61 to 83% of annual loads. Relative annual nutrient loads accounted for 11.3 percent of N and 6.4 percent of P fertilizer inputs. Multiple linear regression models for the FWCs and UALs showed the importance of precipitation, land use, and fertilizer inputs as critical factors controlling transport. The study also demonstrated the water quality benefits associated with shifting fertilizer application from fall to spring.