Assessing the Long Term Impact of Phosphorus Fertilization on Phosphorus Loadings Using AnnAGNPS

High phosphorus (P) loss from agricultural fields has been an environmental concern because of potential water quality problems in streams and lakes. To better understand the process of P loss and evaluate the effects of different phosphorus fertilization rates on phosphorus losses, the USDA Annualized AGricultural Non-Point Source (AnnAGNPS) pollutant loading model was applied to the Ohio Upper Auglaize watershed, located in the southern portion of the Maumee River Basin. In this study, the AnnAGNPS model was calibrated using USGS monitored data; and then the effects of different phosphorus fertilization rates on phosphorus loadings were assessed. It was found that P loadings increase as fertilization rate increases, and long term higher P application would lead to much higher P loadings to the watershed outlet. The P loadings to the watershed outlet have a dramatic change after some time with higher P application rate. This dramatic change of P loading to the watershed outlet indicates that a “critical point” may exist in the soil at which soil P loss to water changes dramatically. Simulations with different initial soil P contents showed that the higher the initial soil P content is, the less time it takes to reach the “critical point” where P loadings to the watershed outlet increases dramatically. More research needs to be done to understand the processes involved in the transfer of P between the various stable, active and labile states in the soil to ensure that the model simulations are accurate. This finding may be useful in setting up future P application and management guidelines

Long-Term Effects of Agricultural Chemicals and Management Practices on Water Quality in a Subsurface Drained Watershed

258 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Double mass curve analysis indicated that the increase of nutrient and herbicide loading began when high amounts of rainfall occurred following chemical application. The primary factor that was found to affect nutrient and herbicide loading was subsurface flow, especially during the growing seasons.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Pathways of runoff and sediment transfer in small agricultural catchments.

Simultaneous field monitoring of runoff and suspended sediment loads from a 30 ha, artificially-drained, mixed-agricultural catchment in Herefordshire, UK indicates field drains are the dominant pathway for the transfer of runoff and sediment to the stream. Surface runoff pathways draining 6·2% of the catchment area transported around 1% of the catchment sediment load, while subsurface runoff in field drains draining 26·5% of the catchment transported around 24% of the sediment load. The explanations offered here for the dominance of drainflow - the spatial limitation of surface runoff generation and low hillslope-stream connectivity of surface runoff compared with subsurface runoff - are also likely to apply to other artificially-drained lowland agricultural catchments in the UK. These catchments are usually on poorly-drained soils, and land management can have a considerable effect on the operation of runoff pathways and the transfer of sediment from hillslope to stream. As a result, subsurface inputs may also dominate sediment transfers in other underdrained catchments. The focus on sediment and pollutant losses via surface runoff pathways means that pollution inputs from subsurface, preferential pathways have been unfairly neglected, and it may be more important to focus on subsurface sediment and sediment-associated pollution inputs for mitigation rather than inputs from surface pathways