Soil samples are a helpful resource for farmers as they provide data to be used for recommendations for limestone, manure and fertilizer.
Soil samples should be taken every two to four years to understand nutrient levels available in the soil for the upcoming crop.
Fall 2024 has been exceptionally dry. In extremely dry conditions soil test results appear lower than they actually are. Delay soil sampling in extremely dry conditions until rainfall has soaked the depth of sampling, usually 6 inches.
Best practices for soil sampling include timing, sampling depth and methods of sampling. The ideal time for soil sampling is during the fall after harvest or early spring before planting.
Allow enough time for lab results to be processed and returned before making a fertilizer application.
For corn and soybeans, samples should generally be taken from the top 6 inches of soil. Pulling cores that are consistent with this depth is important for obtaining consistent results.
Options for soil sampling include grid sampling, zone sampling and whole-farm sampling.
Grid soil samples utilize a composite sample taken in each of the grids ranging from 1 to 10 acres. Grid samples are formed with a pattern of uniform sizes of grids across the field.
Zone sampling factors in field history, yield maps, topography and other management factors creating zones. Composite samples are then collected from each zone forming representative samples.
The final method is whole-farm sampling, this method of sampling gathers subsamples across large areas of the field. A drawback of this method is that not all areas of the field are represented in the sample. If your farm has variability, whole farm sampling would not be recommended.
When taking composite samples, factor in past management strategies in your plan for sampling.
Old feedlots or areas of the field that were managed another way may not be a representative sample area and should be treated differently than an area that has less variability.
Other non-representative areas of a field may include depressions or wet spots, end rows, areas that are heavily trafficked and locations where manure or lime was stored prior to application.
Materials needed for soil sampling include a plastic bucket, soil probe, soil sample bags and a field map denoting where soil samples were collected.
Each soil sample should consist of multiple soil cores collected from various locations within the designated area to ensure a representative analysis. Typically, a sample of 12-15 cores is combined into one sample.
Label the samples and keep records of the sampling locations and conditions. After soil samples have been collected, send the samples to a certified laboratory.
Soil sampling is an upfront cost but may save you money or make you money in the long run.
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