Now is the time to have your soil tested for pH and nutrient levels. It appears that the University of Missouri no longer does soil testing although they can help you find a lab to do that. The lab will provide directions on how to sample and submit those samples. Mostly though you take a trowel of soil from several places you want tested, mix them in a clean bucket, and then send in about 1 pint of that soil for testing.
Those beds can be tested together or seperately if desired.

Here is a link that might be useful: UM CES

The University of MO main campus here in Columbia has an extensive soil lab but it looks from your location in SW MO that you're not close to Columbia. As Kimmsr suggested, contact the UM Extension office in your county and see what they have to say. They may suggest shipping a sample to Columbia if there is not a local lab near you.

They can also give you instructions on how to collect a sample. The normal procedure is to dig down with a trowel (or I like to use a bulb planter) to get a 'core' sample from the top 6-8". Do this in several locations in the area to be tested and mix well in a clean container. Then fill a clean 8-16 oz. jar. If there is a delay in getting it to the lab, I keep it in the frig to preserve it.