Some additional information:
As was mentioned, you can use a shovel and or a spoon besides a soil probe, you will need about 2 cups of soil per sample, packaged in a ziploc bag, I would recommend taping the bags shut as well. Label them with date and sample ID, some labs limit the number of characters, so use simple identification such as Field1A or just Garden, or in my case SESAM1 (Southeast field, sample 1, so I can tell how many samples we’ve taken over time, besides just the date.) I like to send samples via priority mail, usually I can fit two samples into a small flat rate box. Again, tape the box shut, I’ve had a box destroyed once in transit, probably because it wasn’t perfectly closed (bulging soil bags) and caught on something. Include the lab paper with your info on it (so they know where to get their money) and the desired tests.
The reason why we use the Ammonium Acetate ph7 (and Cation Displacement test (for TCEC)) and NOT the usual Mehlich 3 test is because the acid extractant used in the ph7 test is far stronger, thus it extracts a greater amount of nutrients and gives us a far more accurate reading of how much is in the soil. The reason for recommending these 2 labs (Perry and A&L (only for the Cation Displacement test)) is because these labs (and Perry does better than A&L) have compared against others in a small study which showed that they test to the level of the curve. Meaning they leave the extractant working long enough to give us the highest possible reading. That isn’t to say that other labs aren’t accurate, they just aren’t nearly as accurate.