What are good practices for taking a soil sample?

Taking soil samples

For the results to be relevant, the soil sampling protocol needs to be adapted to the crop type, and the sample(s) need to adequately represent the field conditions.

 

Objective

First thing to consider is the objective, i.e. what do you plan to grow? This will dictate whether you should take samples at a single depth or not, and how deep. For instance:

Crop	First depth (in)	Second depth (in)
Berries	0-6	no need
Lettuce, melons, grass	0-6	6-12
Potatoes, corn, pumpkins	0-6	6-24
Hay grasses (e.g. brome, fesuce, pasture), alfalfa	0-12	12-24

 

Representativity

Second thing to consider is representativity, i.e. how homogeneous are the conditions? This will dictate how many samples you should get analyzed. For each area that is relatively homogeneous, a composite sample can be made from which you will extract 1-2 cups to be analyzed. For instance you could scoop a trowel-full of dirt from 6-10 random locations across the homogeneous area and mix that into a pail from which the 1-2 cups representative sample would be extracted. This should be repeated for each area that is relatively homogeneous.

 

References

The following are examples of sample collection protocols developed for agriculture and adaptable to gardening and soil reclamation projects:

Cornell U., 2020. Soil Sampling Protocol. Soil Heatlh Assessment - Part II.
Government of Alberta, 2020. Soil Sampling. Chapter 3.3. pp. 87-97.
Purdue University, 2018. Soil Sampling Guidelines. 6 p.
USDA, 2020. Sampling Soils for Nutirent Management: Helping People Help the Land. United States Department of Agriculture, Natural Resources Conservation Services. 2 p.