How do you take soil samples on 72 acres
Washtenaw County Michigan
Some of your methodology will depend on what the land is used for, but for a general overview see this article from MSU Extension.
You can get an idea of what soil types you have in the parcel using the USDA's Web Soil Survey Tool.
If you would like to submit your sample's to MSU's soil lab, their web page is here.
Let me know if you have any additional questions!