It's obvious from several of the replies in this thread that many
do not know the purpose of soil testing. It's not merely to
determine the pH. It's to determine the overall quality of the
soil. Beyond pH, this includes the relative abundance of
nutrients, not only the primary NPK (nitrogen, phosphorus,
potassium) but also trace elements such as iron, zinc, magnesium,
etc. A good soil test will also determine salinity, which is
important in the western U.S. where both soils and water supplies
might contain excess sodium. Finally, a soil test should determine
the structure (i.e., relative proportions of sand, silt, clay, and
humus).

Since trees, shrubs, and even some perennials can send their roots
well below the level where you have tilled amendments and
nutrients, you should test the native soil before doing any
improvements. (In deep soil, tomatoes can send their roots down 10
feet.) For example, adding gypsum before testing will definitely
skew the results and prevent you from learning what the roots will
eventually find. The results might indicate certain improvements
are not necessary while others are indeed needed. Why spend money
and effort before you know what needs to be done?

If you live in an area where government agricultural agencies do
not do testing, there are likely to be commercial testing labs.
Even in the U.S., not every county has an agricultural extension
office; and in those that do, not every agricultural extension
office does soil testing.

--

David E. Ross, President
Community Foundation for Oak Park
http://www.vcnet.com/~cffop/