The issue of potash stratification is less clear. In no-till, if potash is surface applied, the potash level in the upper one to two inches can get very high while it falls in soil lower down. Tom Bruulsema, Ontario rep for the Potash and Phosphate Institute, says the jury is still out on whether stratification is reducing yields, and therefore whether it would be a good idea to periodically plow no-till soils to spread the potash through the soil profile. Most research to date suggests that corn and soybean roots are able to get all the potash they need from the stratified layer, Bruulsema reports. He's watching the results of new University of Guelph trials to see whether potash uptake may be restricted in years like 1998 when that upper layer is very dry.
Few growers rely on a pure no-till system.
Instead, most use a multiple coulter system to work up an in-row seed bed at planting. That tillage could help spread the potash. As well, Bruulsema says, techniques such as shallow or deep banding may be equally effective as tillage at placing the potash where it's needed, just as no-tillers use 2 X 2 bands at planting to apply phosphate. More research is needed, Bruulsema believes. Clarence Swanton is warning that growers who plow their no-till soils should prepare for several years of tough weed control.