Nutrient transport by overland sheet flow on sites containing swine slurry

Authors: Gilley, John

Submitted to: International Soil and Water Conservation Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2024
Publication Date: 4/13/2024
Citation: Gilley, J.E. 2024. Nutrient transport by overland sheet flow on sites containing swine slurry. International Soil and Water Conservation Research. 13 (2025) 145-151. https://doi.org/10.1016/j.iswcr.2024.04.001.
DOI: https://doi.org/10.1016/j.iswcr.2024.04.001

Interpretive Summary: The physical processes affecting the transport of nutrients by overland flow from land application sites are not well defined. This study was conducted to identify the mechanisms influencing nutrient transport on sites containing swine slurry. The data which was examined was obtained from field rainfall simulation tests performed on field plots located on sites in southeast Nebraska. In those studies, inflow was added to the top of experimental plots in four successive increments to simulate runoff rates occurring at greater downslope distances. It was observed that phosphorus and nitrogen transport rates increased in a linear fashion with runoff rate on sites containing swine slurry. Two mechanisms were thought to influence nutrient transport: the quantity of phosphorus and nitrogen that is released by manure at a particular runoff rate and the amount of overland flow available to transport the released nutrients. It was shown that nutrient transport rates can be related to runoff rate. If nutrient transport rates can be linked to runoff rates, nutrient delivery to the edge of a field can be estimated, and many of the analytical procedures used for routing runoff on upland areas can be expanded to also include water quality constituents. Further testing of the transport equations is needed for other types of slurry applied under varying cropping and management conditions.

Technical Abstract: The physical processes affecting the transport of nutrients by overland flow from land application sites are not well defined. This study was conducted to identify the mechanisms influencing nutrient transport on sites containing swine slurry. The data which was examined was obtained from field rainfall simulation tests performed on either 2 or 4 m long plots located on sites in southeast Nebraska, USA. In those studies, inflow was added to the top of experimental plots in four successive increments to simulate runoff rates occurring at greater downslope distances. Runoff rates on the experimental sites ranged from 2.3 to 21.2 L min-1 and equivalent downslope distances varied from 5.2 to 108 m. It was observed that P and N transport rates increased in a linear fashion with runoff rate on sites containing swine slurry. Two mechanisms were thought to influence P and N transport: the quantity of P and N that is released by manure at a particular runoff rate and the amount of overland flow available to transport the released P. It was shown that P and N transport rates can be related to runoff rate. If nutrient transport rates can be linked to runoff rates, nutrient delivery to the edge of a field can be estimated, and many of the analytical procedures used for routing overland flow on upland areas can be expanded to also include water quality constituents. Further testing of the transport equations is needed for other types of slurry applied under varying cropping and management conditions.