Soil Sampling

Soil sampling is key to any good fertility program. But which system is best for you?

Composite Sampling

The most basic form of sampling, composite samples take cores in a semi-randomized pattern across the field. All cores are combined to determine average fertility values. While cost effective, the values are only AVERAGES. If the field is composed of high and low pH values, for example, the average may look good. However, this value may never exist in a managable area.

Grid Sampling

Grid sampling was created to find spatial variablily in large fields. The 2.5a grid was created simply by taking an even amount of samples in a standard 1 mile survey, as is found in most of the US and Western Canada. In a quarter section, a grid of 8×8 points (64 samples) samples was even and easy. No prerequisite work is required, and the samples will show broad variability. While this works well in the West, Ontario soils change more rapidly. There is also much higher value in the crops. Many times the standard grid points miss critical land features.

Modified Grid

There is nothing in the grid protocol that suggests that 2.5a square blocks will provide any tangible benefit. A skilled sampling technician can and should move the grid points while in the field to properly capture the variability in a meaningful way. Examples include moving a point to the centre of a weedy patch, the top of a hill, or the bottom (or near bottom if ponding is an issue) of a depression. This will more accurately capture the specific zones, though the interpolation on the software used to contour the points will not have any way of knowing a zone’s extent.

Zone Sampling

Zones for sampling provide a much more detailed and accurate picture of the soil variability. However, they take pre-planning, which ultimately leads to higher cost. Depending on the field, this can yield much more usable results

Soil Scannig

Several soil scanning methods are available, notabley electrical conductivity and gamma-ray spectroscopy

Topograpy

Lanforms often share similar properties.

Combination

Combining a soil scan with the topography to delineate zones is my preferred soil sampling method. Sand in a valley behaves much different than on a hill.