Trinklein says laboratory tests are more accurate than over-the-counter test kits and provide specific recommendations on fertilizer and other amendments based on what you want to plant, whether it's flowers, vegetables, turf or trees.
Collecting the sample
While there are tools specifically designed for extracting soil samples, Trinklein says an ordinary garden spade will do.
Remove a slice of soil, going about 7 inches deep. Remove the soil on either side of the slice to leave a strip about an inch wide and 7 inches long. Take about five samples from random spots in the garden, taking care to avoid depressions and berms, which do not give good soil samples, Trinklein said.
Mix the five samples thoroughly to create a composite. Collect about one pint of the composite. You can get free sample boxes from your county MU Extension center along with the form that should accompany your sample. You can also download the form at www.extension.missouri.edu/MP555. Results will arrive by mail in about a week or two.
Results and recommendations
The soil test report will include recommendations for adding specific nutrients, measured in pounds per 1,000 square feet (or pounds per acre for farms), based on the needs of the plants you specified in the form included with your sample.
Commercial fertilizers generally contain a mix of three key nutrients-nitrogen, phosphorus and potassium, and the label will list the percentage of those nutrients in that order. For example, a 10-pound bag of fertilizer with a grade of 5-10-5 would contain a half-pound of nitrogen, a pound of phosphorus and a half-pound of potassium.
Another key part of the soil test report is the pH, a measure of how acid or alkaline the soil is. The lower the pH, the more acidic the soil. Soil pH has to fall within a fairly narrow range for plants to make full use of nutrients. Most fruits and vegetables grow best in soil with a pH of 6.0-6.5, though some plants prefer more acidic soil.
"The tendency in nature is for soils to become more and more acid as plants use the nutrients," Trinklein said.
Because of this, you may need to increase pH by adding lime-an acid-neutralizing material typically made from crushed or ground limestone. If the soil has an unusually high pH or you are growing plants that prefer acidic soil, such as blueberries, you may need to apply sulfur to increase acidity.
Source: AGEBB