In most places (here in the States), there is a "County Farm Agent's Office". Different places call it by different names, but it deals with Agricultural issuses of all sorts. They offer free (or at least vert cheap) laboratory testing of things like your local soil, fertilizer, etc. Many of these services are offered through, and in conjunction with, your local university, but are usually administered by the "County Farm Agent". Remember, this is usually a County (or State) Government operation - not a "for profit" laboratory.
Do some checking around and find your local "County Farm Agent".
