Improved Soil Sampling

When 2.5 acre (1 ha) grids are overlaid on a soil EC map, it's readily apparent that soil doesn't change on a square grid. Out of the four 2.5 acre grids on this map, only sample #4 clearly "found" the heavy soil snaking through each grid.  It's also easy to see that 2.5 acre grids aren't small enough to capture the variability in the field. 

In fact, grids overlaid on EC maps often reveal that there is as much variability within the 2.5 acre grid as there is in the entire field.

How can soil EC help?

Directed grid density instead of conventional grids

One way to use soil EC maps is to sample at a 2.5 acre intensity, but place the points where the EC map shows the soil is actually changing, as shown below. Sampling this intensively is most appropriate where previous farm history and manure applications have added manmade variations in nutrients.

Management Zone Sampling Sampling density and lab analysis costs can be reduced by dividing a field into management zones, based on soil EC and soil texture variability. In this example of zones, the number of samples was reduced by 50% versus 2.5 acre grids.