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Competency Area 7: Non-point source pollution AEM

PO 71. Describe the main sources of agricultural Non-point source (NPS) pollution and their origins.

  1. Nitrogen
  2. Phosphorus
  3. BOD (Biological Oxygen Demand)
  4. Sediment
  5. Pesticides
  6. Pathogens
  7. Silage leachate
  8. Chemicals and toxins
  9. Processing and wastewater

Nitrogen – sources are from runoff, tile discharge and leaching losses originating from fertilizer and manure applications in excess of crop needs and requirements. The timing and the amount of application relative to crop growth is critical. For example, a single large application of nitrogen fertilizer to corn in the spring and while plants are still small often results in substantial losses during spring rains and thunderstorms. Using split applications and timing it to crop growth needs results in more efficient use of the applied N. Fertilizer N applied in the fall will generally be denitrified or leached away before it can be used by the following year's crop. The fate of manure losses differ from those of fertilizer, with volatilization, nitrification, and denitrification occurring at different times and at different rates depending on surface or incorporation application techniques.

Phosphorus – sources are from eroded soil (as particulate P), soluble P in runoff and in some tile discharges from soils testing high in P; and from suspended and dissolved organic P in manure runoff and in some tile discharge. High P concentrations can be found in runoff, and in some cases tile drain discharge, especially when rain follows shortly after surface manure applications.

BOD (Biological Oxygen Demand) – sources are from the application of fresh manure and agricultural process wastewaters, especially if rain immediately follows surface applications. [The BOD arises from the need for oxygen to complete decomposition processes of the organic materials, and thus it lowers the oxygen in receiving waters which may cause fish kills.]