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, 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.