The amount of soil collected and sent for analysis does make a huge difference. I know many labs air dry samples before grinding. Other laboratories, like Midwest Laboratories dry soil at a consistent temperature to remove as much moisture from the soil as possible for analysis. Each year, Midwest Laboratories conducts studies specific to drying temperature and quality/consistency with respect to heat across all drying areas.
The general rule is 1-1.5 cups of soil. This amount can vary depending on the type of soil. Midwest Laboratories supplies its account holders with soil bags. These soil bags indicate a red line as to how much soil you should put into the bag. Too much soil can result in some soil being discarded because there simply is too much. Obviously this can cause issues, especially if the sample is a composite sample made up of several soil/land addresses.
Just as too much soil can be an issue. Short-samples can also cause issues with respect to not providing an accurate analysis. This fall, I have spoken to some samplers who say the ground is very hard and compact. This can make it to tough to pull a 4-6 inch sample for general soil testing.
Obviously, soil sampling begins with the sampling process, but this article serves as a reminder of the many steps/processes that need to be completed to provide accurate soil testing data for growers. If you have further questions, contact a member of the Soil Client Services team at Midwest Laboratories.
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