The scales tipped in 2011, when more than half of all samples tested by AGVISE laboratories (Northwood, ND and Benson, MN) combined, were grid or zone samples. Then in 2012, that increased to 60% (see table). The table also shows the state/province breakout by year back to 2008, with a steady increase in grid/zone samples in MN, SD and ND. Most of the ND, SD and MB precision samples are 2-depth (topsoil + subsoil) “management” zone samples. Most of the MN precision samples are 1-depth (topsoil only) grid samples, with some 3-depth (topsoil + subsoil + deep subsoil) in the sugarbeet growing areas.
Much of the MN topsoil grid sampling is moving to the early summer (end of May through early July) time frame, as shown in the chart above. The amount of early summer sampling has tripled since 2007 in the Benson lab, with many growers, agronomists and retailers seeing the advantages of getting this done early instead of waiting until after harvest to sample.