There are many definitions of incorporation tillage. Many years ago it was associated with inversion of the soil. Later it became digging down 8 to 10inches and stirring the soil while taking place with a fertilizer application and in some cases impregnated with herbicide. For lack of a better term, incorporation today may likely mean just mixing the top 3 to 4 inches of soil to make good soil to fertilizer contact while keeping nutrients high in the rooting zone.
Not only does this light tillage mix fertilizer, it also creates a disconnect of hydrologic pathways, like cracks and earthworm holes, that run directly to tile.
On December 12, 2014 the 4R Nutrient Stewardship Certification Program held a workshop for retailers and farmers in Toledo, OH. Speaker Kevin King, engineer with USDA Agricultural Research Service, is heading up 38 edge of field study sites. These sites include 19 pairs of fields with before and after studies using multiple variations of tillage, cover crops, fertilizer applications, gypsum, etc. The goal is to eventually determine which practices have the most potential to reduce phosphorus losses from farmland.
One example that King shared was actually inadvertent, but able to give some preliminary results. A grower that is hosting an edge of field study had variable rate fertilizer applied according to grid samples taken. Upon completion of the VRT fertilizer application, the grower was able to lightly incorporate or mix the fertilizer in the top 3 to 4 inches on approximately one half of the field. Within 3 days the location received an unexpected 2 inch rainfall that was able to produce some unplanned and preliminary results supporting light incorporation. Dissolved Reactive Phosphorus (DRP) was measured at 1ppm from the tile of the field that was lightly incorporated. The tile of the field where the fertilizer was not mixed with the soil at all yielded 5ppm, not to mention what may have run off the surface. Once again, this only a preliminary observation but points to great benefits for water quality improvements as well as minimizing profit losses for growers.