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Wisconsin P Index Approach to Assessing Soluble P Losses from Cropped Fields

Wisconsin P Index Approach to Assessing Soluble P Losses from Cropped Fields. L.W.Good Department of Soil Science University of Wisconsin Madison. Average Dissolved P (DP) Losses in runoff are calculated for each c rop y ear for two P sources:. DP released from soil surface

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Wisconsin P Index Approach to Assessing Soluble P Losses from Cropped Fields

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  1. Wisconsin P Index Approach to Assessing Soluble P Losses from Cropped Fields L.W.Good Department of Soil Science University of Wisconsin Madison

  2. Average Dissolved P (DP) Losses in runoff are calculated for each crop year for two P sources: • DP released from soil surface • DP released from fertilizer on surface

  3. Example Field Somewhat poorly drained silt loam 1% slope Within 300 feet of stream Soil test P = 35 ppm Bray1 P Year 1: Corn grain, Fall chisel plowed, spring disking, Maintenance fertilizer (DAP) incorporated by tillage spring. Year 2: Soybean, Maintenance fertilizer (DAP) broadcast spring Year 3: Winter wheat, Maintenance fertilizer (DAP), broadcast fall

  4. DP from Soil = Surface Soil Test P (STP)x P Extraction Coefficient x Runoff (RO) Volume x Units Conversion FactorSurface STP = Plow layer STP x Stratification FactorMaintenance Fertilizer P = Crop P Removal, so plow layer soil test P not expected to change year-to-year, but surface soil test P will change with tillage.

  5. DP from Fertilizer =Fertilizer P on surface X Runoff/Precipitation x O.034 exp (3.4 Runoff/Precip) The ratio Runoff/Precipitation is for the season of application and can be thought of as the potential for precipitation water to runoff, rather than infiltrate

  6. Total Estimated Average Annual Dissolved P Losses in Runoff for Example Field

  7. WI P Index “Modeling” Approach • Tested with field runoff data • Shown to be providing a good estimate of field runoff dissolved P losses when measured runoff volume and precipitation are used in the equation • Current work on Wisconsin P Index focusing on testing methods of assessing management and soil affects on average runoff volume

  8. Vadas -- APLE 2.4

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