The P Index with In-Field Conservation Practices

In-field practices that reduce erosion and runoff can be evaluated in the P Index as long as they can be found in the RUSLE2 databases used in SnapPlus. Practices that can be evaluated include changing crop rotations,Screen Shot 2013-05-05 at 9.52.36 PM reducing tillage intensity, planting cover crops, working the field on the contour, strip cropping, and in-field grass contour buffer strips.  Below is an example of the kind of comparison that can be made, showing the reduction in P Index with a switch to no-till from fall-chisel plowing.  The Particulate P Index decreased to less than a third of its original value, but the estimated average soluble P losses from manure increased because manure cannot be incorporated with no-till.


Figure –  Rotational average P Index from eroded soil (Particulate P I) , dissolved P from soil (Soluble P I soil), and dissolved P from manure (Soluble P I manure) for a fall chisel-plowed and no-till Loyal silt loam field with 4% slope, 47 ppm soil test P, 2.5% organic matter, with fall applications of 10,000 gallons of liquid dairy manure before corn. The P Index is shown by component: Particulate P I is P in eroded soil, Soluble P I soil is dissolved P from soil, Soluble P I manure is dissolved P from manure.