Phosphorus runoff research has been limited on soils that are calcareous to the surface. We followed the National P Project protocol using rainfall simulation to evaluate the relationship between soil test P levels and runoff P losses on three Great Plains agricultural soils in Kansas, Nebraska, and Colorado.

Results

• Olsen and Mehlich-3 soil extracts both work well for prediction of soluble P in runoff from calcareous soils.
• Although soil testing is a good predictor of soluble P, it is not predictive of total P loss (including the sediment carried P).
• The 0-15 cm sampling depth resulted in higher R2 values more often than the 0-5 cm sampling depth; therefore, normal soil sampling technique can be used to predict soluble runoff P.
• Overall, soil samples taken before rainfall simulations outside the plot area were most predictive of soluble runoff P.
• Results from Event 1 were most predictive of runoff P concentrations, probably due to the surface sealing that occurs on these soil types.
• The three locations resulted in different regression equations with different slopes, intercepts, and R2 levels. Therefore, they should not be extrapolated to other soil types.

Graduate Student: Ron Schierer, currently agronomist with USDA-Natural Resources Conservation Service in Greeley, CO.

Co-Principal Investigator: Reagan Waskom

Cooperator: Alan Schlegel, Kansas State University

Farmer: Bob Kraft

Funding from the USDA-Natural Resources Conservation Service and the U.S. Environmental Protection Agency Pollution Prevention Program

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Last updated November 5, 2007 by Webmaster