Soil test are important for determining P and K fertilization requirements. Though Purdue has been out of the soil testing business for many, many years, there is a list of certified soil testing labs at http://www.agry.purdue.edu/ext/soiltest.html. Taking an soil test is even more important than where it is sent for analysis. More information is available at http://www.agry.purdue.edu/turf/pubs/ay-18.pdf