When and how often do you get a soil test?

We bought 20 acres last year that we were told was in hay production prior to land put up for sale.  When we looked at the land, it looked pretty weedy and lots of horse dropping.  Neighbor to the left said to mow it often for a year or two and the hay would come back.  Neighbor to the right said the property hadn't been hayed or mowed in 10-15 years.  If we had known how much we didn't know about hay, we probably would have passed on the sale.  But now it's ours and we have to get it in shape.

 

Is it too late for a soil test this year, or too late to adjust the soil once we get a test?

When and how often do you get a soil test?