University of Illinois Extension

Soil Test this Fall

Testing your soil does not take much time and the benefits of doing so can mean being able to produce more vegetables for fresh table use all season long in 2013, said a University of Illinois Extension horticulture educator.

"Gardeners could test their soil anytime," said Richard Hentschel. "Fall is the better time, having had the season to allow any fertilizers and organic matter applied to react with your garden soil and provide you the best possible soil test levels."

Soil Test

A typical soil test reveals the levels of "Big 3" nutrients used by vegetable plants, nitrogen, phosphorus and potassium. The soil test will also reveal the level of soil acidity or alkalinity, shown as the pH on your results. A pH of between 6.0 and 7.0 is the general goal.

"If gardeners have added lots of organic matter over the growing seasons, a pH of 6.0 to 6.5 is likely and more favorable to the vegetables," he noted. "Organic matter can be your own home-grown composts, additions of well-rotted animal manures and even the annual turning under of disease free vegetable plant parts adds to the percent of organic matter measured in the soil.

"A level of 3-4% is considered pretty good. One of the reasons it is so important to have the right pH is nutrients that would normally be available to the plants for good growth are not present if the soil pH is out of the 6.0 – 7.0 range."

A typical soil test will also provide you the levels of phosphorus and potassium. These two along with nitrogen are used by the plants in the greatest amounts. Phosphorus and potassium are stable in the soil and those levels remain relatively constant over time and adding more just in case is not suggested and can contribute to the degradation of ground water. Nitrogen is water soluble and the level changes easily. If your soil test provides the nitrogen level, keep in mind that by the time the results are back, that level has likely changed.

"Gardens get better over time even with time since the root systems that remain in the garden add to the organic matter content and any mulches that get turned under help too," said Hentschel. "Gardens in newer subdivisions will greatly benefit from additions of organic matter as the soil has been highly disturbed and organic matter helps in the restructuring of the soil profile besides providing nutrients and water holding capacity."

Taking a soil sample is really easy in the vegetable garden. Stay away from the edges and take the samples nearer the middle of the garden. The samples taken need to be a vertical sample, six to eight inches deep where most of the vegetable plants find their food.

Using your garden shovel or spade, dig a small hole to that six to eight inch depth. Using the shovel or spade, slice down one edge of the hole and you will get that important vertical sample. Repeat this process several times to be sure you get that representative sample for the actual test. Most labs only require a small butter dish full of soil and others will provide the gardener with small paper bags to submit the soil sample.

"You can even use a larger bulb planter to take your samples, if it will go the six to eight inches," said Hentschel. "If it is possible after your test results and recommendations return, put those amendments down yet this fall to let them begin to react with the soil."

To find a soil testing laboratory near you, Extension has a website (http://urbanext.illinois.edu/soiltest/) to get gardeners started. Locate a lab that can provide recommendations for the home garden. Your county Extension office may have a listing of local labs too. To find out where a county Extension office is near you go to: http://web.extension.illinois.edu/state/findoffice.html