Phosphorus in soils is almost entirely associated with soil particles. When soil particles are carried to a river or lake, P will be contained in this sediment. When the sediment reaches a body of water it may act as a sink or a source of P in solution. In either case, it is a potential source of P that may eventually be released.
Most soils have a large capacity to retain P. Even large additions of P will be mostly retained by soils provided there is adequate contact with the soil.
Increasing the amounts of phosphate in soils results in increased levels of phosphate in soil solutions. This will generally result in small but potentially important increases in the amounts of phosphate in water that passes over or through soils.
Phosphate in soils is associated more with fine particles than coarse particles. When soil erosion occurs, more fine particles are removed than coarse particles, causing sediment leaving a soil through erosion to be enriched in P.
Source: http://www.extension.umn.edu/agriculture/nutrient-management/phosphorus/the-nature-of-phosphorus/
Understanding phosphorus in Minnesota soils
http://www.extension.umn.edu/agriculture/nutrient-management/phosphorus/understanding-phosphorus-in-minnesota-soils/index.html
UMN soil test info
http://soiltest.cfans.umn.edu/our-methods/
Soil Phosphorus overview
https://www.youtube.com/watch?v=PXLAZznE67Q
Maximizing Phosphorus Efficiency: An Introduction (NACHURS® Liquid Fertilizers) - ???
Very good intro and history of P fertilizer but is questionable source
https://www.youtube.com/watch?v=Zk0YrZpThkU
Lake Independence (landowner lawsuit)
Dairy owners James and Paul Merz agreed to shut down much of the operation and improve manure handling to resolve a lawsuit filed last summer by the Lake Independence Citizens Association and 21 individual homeowners. It also estimated that the Merz farm contributed about 166 pounds of phosphorus per year. One pound of phosphorus can produce 300 to 500 pounds of algae in a lake.
http://www.startribune.com/local/west/207651991.html