Soil Sampling

Aerial photo of land with boundary outline
This is the most basic method of soil testing, as only one sample is analyzed per field. Results indicate a general idea of soil fertility across the field.

What it is:

A soil test is essential to determine soil fertility levels and make good nutrient management decisions. There a many options when determining what type of sample is right for your farm. At a minimum, one sample (15-20 cores per sample) from the tillage depth, should be taken per 20 acres of field size. Samples can also be taken by grids or by zones. The intensity of soil sampling can give the producer more detailed information about their field’s nutrient needs. For example, Surface (0-6") samples typically test for OM, Phosphorus, Potassium, pH and salt levels and subsurface (6-24") test for nitrate-nitrogen and other mobile nutrients that may have leached below the 6" layer. Samples (~2 cups) are collected, air dried, bagged and shipped to testing lab.

Aerial photo of land with boundary outline and markers where soil cores were extracted
Ag Retail outlets standard size is 2.5 acre grids. Sample cores are taken at each point to be analyzed. The results are then interpolated in a GIS mapping software to come up with the result maps in grid form. These results represent soil fertility on a grid basis.

How does it help:

Nutrients applied in the right amount can increase yields, reduce production costs, and prevent surface and groundwater pollution. When soil sampling data is overlapped with yield mapping data, a clearer picture can be developed on where deficiencies are occurring in the field. More detailed soil sampling can also more accurately represent where fertilizer is needed most which will result in more efficient use of that fertilizer.

Edge of field monitoring research shows that soils with higher soil test phosphorus reading are more likely to have nutrient loss. By maintaining soil test phosphorus levels within the Tri State Fertility Guide recommended ranges, the producer can reduce their impact on downstream bodies of water.

Aerial photo of land with boundary outline management zone outlines
Management zones are created in a GIS mapping software using aerial imagery, soil type data, yield data, and topography maps. These zones can vary in size depending on different variables. Multiple sample cores are taken throughout a zone to accurately represent each zone. These results represent soil fertility on a zone by zone basis.

Planning ahead:

You should plan how the field is to be sampled before you begin. You should plan how you will divide the field into sampling areas, then always use the same areas in the future. Sampling should be conducted as close as possible to planting time. A soil map, available at the local SWCD/NRCS office will often be helpful. Some factors that might cause you to sub-divide the field into separate sampling areas are...

  • The size of the field
  • Different soil types
  • Different topography
  • Different past usage (previous crops, livestock confinement, fertility practices, etc.).
  • Fertilizer application capabilities
  • Different past crop performance

Maintenance:

Soil tests should be updated every 3-4 years at a minimum.