National Benchmark P
Predicting Runoff Losses from Soil Test P on Calcareous Soils
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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