By Greg LaBarge and Harold Watters, Ohio State University Extension
Simply put, the goal of soil sampling is to make a fertilizer recommendation for crop production.
- To provide that recommendation, calibration studies are done to measure crop response.
- For Ohio, the Tri-State Fertilizer Recommendations provide the calibration study history for recommendation development. For 2020 we just rolled out the latest “Tri-State” recommendations.
It’s about statistics. We want to take a representative sample, meaning that the sample should represent the fertility level of the area we sampled.
- Choose sample areas in the field that have similar crop yields, crop rotation histories, fertilizer application methods and sources of applied nutrient.
- Fields or field areas with a history of livestock production (a former pasture, had manure applications or produced hay) or other unique characteristics may require a different sampling strategy.
- Field areas represented by any single sample should not be greater than 25 acres.
- Use of a yield monitor, soil maps, and grid sampling can lead to development of crop management zones, easing the burden of future sampling.
Understand that a single soil sample is not a single core but is a composite of numerous cores collected over the field area represented by the sample.
- Where broadcast applications have occurred a composite sample of 10-15 cores is suggested.
- Where a history of banded application exists in a field or manure application, then increase the number of cores to 20 or 25.
Nutrients in the soil are naturally stratified with higher nutrient levels on the surface. This is due to plant residue breakdown and fertilizer placement. Each core taken should be taken to the same depth in the soil profile. We used the 8-inch depth for the 2020 Tri-State update.
The primary goal is to measure the ability of the soil to provide the soluble nutrient needed for crop production for two of our three macro nutrients (phosphorus and potassium) plus measure soil acidity which governs availability of micronutrients and other soil functions. A very important secondary goal is to compare soil test results over time. This systems approach is what is becoming known as “adaptive management.” No soil test result should be considered in isolation, look at past results before making major modifications.
Harold Watters, Extension Field Agronomist, works out of the Extension office in Bellefontaine and can be reached at firstname.lastname@example.org or by phone at 937 604-2415.