In order to use the OSU Extension publications to interpret your soil test results it is important to read through the publication that is relevant to your cropping system before taking soil samples. Crop guidelines and recommendations are calibrated to specific soil sampling depths. Often this is the top six inches, but some recommend two, eight, twelve, or even twenty-four inches.
In order to capture the spatial range of variation and produce meaningful results we recommend the following sampling procedure:
- Each soil sample should be taken to the same depth, according to your extension publication recommendation. However, there are situations where deeper samples are needed particularly when concerns arise over drainage issues.
- Each soil sample should be dug straight down so that the volume of soil you pull from the five-six inch depth is the same as the volume from the top one inch.
- Each management area should be sampled separately.
- A management area is one that has the same kind of land form (valley bottom, hillslope, top of the ridge) as well as the same past management practices. If you have a totally flat two acre pasture that has had hay on it for five years that would be one management area. If you have a little hill with ponding frequent at the bottom and a cattle grazing on the top of the hill you would have a minimum of three management areas.
- You should take 5-20 soil samples (depending on the size) spaced across the land to try to capture the variability from each management area. Combine these subsamples from one management area into one sample bag to account for the range of characteristics in that site.
- If you need to have nitrate, ammonium, or any microbial traits analyzed your samples should be kept cold (ideally ~4C or 40F) until they arrive at the testing laboratory. An ice pack in an overnight package will do the trick for sending most samples, but an icepack in a cooler may be necessary.
- Samples should be sent in a sealed and labelled plastic bag. You will also want to write down a note in your own records about where the samples came from, the depth, and the date sampled.
- All analyses can be done if you send about one quart sized bag per management area.
Soil is highly variable both spatially and temporally. For more details on what time of year, why you should sample, images of determination of management units, and the analyses you should request we recommend a great extension publication:
A Guide to Collecting Soil Samples from Farms and Gardens - EC 628
Samples should be sent to:
Oregon State University
Central Analytical Lab
3017 Ag Life Sciences Bldg
Corvallis, OR 97331