Tim Mundorf, Field Representative, Midwest Labs, says that, for the most part, the Omaha, NE-based soil test lab doesn’t get real involved in how the client takes the samples.
“We certainly stress the importance of a good sample that is representative of the area that is being sampled,” he adds. “And we stress consistent sampling depth so that the numbers do not change over time because of depth variation.”
Beyond that, Mundorf shared these six tips for service providers utilizing automated soil sampling technologies out in the field:
- Check that the sampler is pulling from a consistent depth. Shallow samples tend to show higher nutrient levels while deeper samples tend to lower nutrient concentration.
- Make sure all of the soil core makes it into the sample collected. It’s ok to mix cores together and subsample that group into a smaller sample size, but if your equipment leaves a portion of the sample core on or in the ground every pull you are skewing your results.
- Make sure drills get all of the soil off the flighting into the sample to the depth intended. If you leave the bottom inch or two of soil on the flighting your results will generally show higher nutrient levels because you are effectively pulling a shallow sample.
- More cores is better than less cores. I like a minimum of 10 cores when grid or zone sampling to smooth out variation and get a number that is more representative of the total area I am sampling.
- Watch out for fertilizer bands. These tend to skew results by how many cores are pulled from the band vs. the non-band area. A good ratio of band to no band is probably 1:10. Many times you don’t know where the band is located so watch your results and take unusually high numbers with a grain of salt.
- Be careful in recently tilled soil that you are getting complete cores and not hitting a void and getting a partial core.
Mundorf also notes that, for those still using a hand probe, most of the above tips are relevant as well.