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Nitrogen Balance and Use Efficiency in the Calapooia River Watershed, Oregon, United States
Citation:
Lin, J., S. Pearlstein, J. Compton, W. Matthews, AND S. Leibowitz. Nitrogen Balance and Use Efficiency in the Calapooia River Watershed, Oregon, United States. International Nitrogen Initiative, Melbourne, AUSTRALIA, December 04 - 10, 2016.
Impact/Purpose:
Humans have substantially altered biogeochemical cycles by introducing excess nitrogen (N) to the environment via the processes of food production, fossil fuel combustion, and point source discharge. Excess N contributes to numerous negative impacts on human health and the environment, such as eutrophication, drinking water contamination and hypoxia. It is urgent to study the sources and inventory of environmental N in watersheds, and to develop approaches to improve the N use efficiency, particularly in agricultural regions. This work uses data from an area dominated by agricultural uses to build a small-scale N inventory, and to quantify N sources, fate and effects on local air and water quality endpoints. The work is supported through EPA's Safe and Sustainable Water Resources Program Task 4.03C (Monitoring and multimedia assessment approaches for verifying reductions). The team brings together expertise in biogeochemistry, soil science, watershed modeling, landscape ecology and agronomy to develop a case study of increasing local watershed-scale nitrogen use efficiency.
Description:
Reducing nitrogen (N) release into the environment through greater N use efficiencies (NUE) is a current challenge in watershed management. Examining N sources and sinks at local scales allows for better watershed-scale N use, for example when considering the tradeoffs between the uses of animal waste from Concentrated Animal Feeding Operations (CAFOs) as a resource compared with the use of synthetic fertilizers. We use data on land-use, CAFOs, N deposition, stream chemistry, and crop-level and county-level fertilizer use to assess the N inputs, exports and retention in the Calapooia River Watershed (CRW). The CRW is influenced by intensive agricultural activities, mostly in grass seed crops. We determined that at the CRW scale, annual TN export is 25% of the inputs. Nearly 48% of the total area has a net TN input of 100-200 kg N ha-1 yr-1, dominated by agricultural land. About 41% has an input of <100 kg/ha/yr and 2.4% >200 kg N ha-1 yr-1. Almost 50% of the annual hydrologic N yield occurs during wet winter and reaches 50 kg ha-1. The minimum TN yield as low as <1 kg ha-1 happens in dry summer. The effect of crop type on NUE is estimated based on N retention calculation and land use data. A manure-distribution model will be built to help improve manure NUE and prevent excess fertilizer application. Information on N balances will also be combined with local groundwater and drinking water nitrate level to assess the implications of N release for water quality and human health.