by Wayne Flanary, regional agronomist
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Growers should focus on having fields soil sampled this fall before weather turns bad. Soil sampling and then the testing of the soil will provide you with information about the levels of nutrients in the soil. This information can then be used to plan the kinds and amounts of nutrients required to grow next year’s crops.
The cost of fertilizers has increased considerably compared to last year. The use of soil sampling and testing is more important than ever.
Soil samples can best be taken using soil probes which look like a pipe with a cut-out on the side of the tube so the soil can be easily removed and placed into a container. There are many different types of soil probes and most Extension offices have one that you can borrow.
The sampling depth should be from six to seven inches deep. The soil probe should be marked on the outside of the tube so one can accurately sample to the correct depth. Taking samples too deep and too shallow increases the risk of error.
Once you take the soil core, you place this into a container. The container is often a bucket as you are going to mix many cores together to obtain a composite sample. Be careful as the type of material the bucket is made out of can cause soil tests to be inaccurate. The best material to use is plastic, as galvanized buckets can cause soil tests to be inaccurate.
Many cores should be taken to make a composition sample. More cores increase the accuracy that the composite sample represents for the particular area of the field. The cores are mixed thoroughly and then a sub sample is taken which is sent to the lab to be analyzed.
If you are grid sampling, most cores are taken in a particular location in a field that is geo-referenced and so you can re-sample this site in the future. Often several cores from this small area in the field, called point sampling, are taken. Later, computer software is used to show the results from various sampling points and is used to generate spreading maps for nutrient applications.
If you are using standard composite samples, do not sample more than twenty acres per sample.
Knowing the field history can aid you in determining a soil sampling plan. Many fields we have today were at one time small farms. Often you may find levels higher where livestock was grown.
Last of all, soil samples are good for three to four years. Soils have the ability to buffer change and so levels do not change much from year to year. Therefore, we do not recommend soil testing every year unless for mobile nutrients.
For more information contact Wayne Flanary at (660)446-3724 or Heather Benedict at (660)425-6434, Regional Agronomists with the University of Missouri Extension.