Soil testing is the single most important guide to the profitable application of fertilizer and lime. Testing the soil helps determine how much fertilizer and lime is going to be applied to a given area. Soil tests do not measure the exact amount of a nutrient taken up by the plant. What soil test is meant for is to predict the amount of nutrients needed to increase the level that is in the soil.
Late summer and fall are the best seasons for collecting soil samples because potassium test results are most reliable during these times. The potassium soil test tends to be cyclic, with low test levels in late summer and early fall and high test levels in late January and early February.
Samples should be done every 3 years. To improve the consistency of the results, sampling should be done at the same time. A soil tube is the best implement for taking soil samples, but an auger or spade also can be used. If you use a trowel or spade, dig a hole and then cut a thin slice down one side.
Once the location has been identified, collect and composite five-soil core samples 1 inch in diameter to the proper depth from within a 5-foot radius around each point. Mix the soil samples together in a bucket. The five soil cores taken with a tube (or other implements) will give you the composite samples of about 1 to 2 cups.
The depth to which the sample should be taken depends on what plants are growing there now, or which ones will be planted. For example, take soil samples in sodded areas to a depth of 3 to 4 inches; for shrubs and trees 12 inches is used; and for flowers and vegetable crops 6 to 8 inches.
When placing the samples in the bucket, do not include roots or debris. After mixing the soil samples together, place two cups of soil in a plastic bag. Then place the bag in a strong container, carton, or can. Send out the samples as soon as possible, thus keeping the soil samples below 75 degrees. Make sure to mark the bag where you took the samples. Also, don't mix shady areas with sunny areas, keep these as separate samples when sending them to a laboratory.
Label each sample with your name and address. If more than one sample, label each samplewith a number to tell you from which area they were taken. Mark each sample "flower garden", "front lawn", etc. Include information describing what was grown in the garden last year and what has been done to the soil, such as adding manure or other organic matter.
Some recommended soil tests for making decisions about lime and fertilizer use are the water pH test, which shows soil reaction as pH units; the Bray P1 test for plant-available soil phosphorous; potassium (K) test; and boron for alfalfa. Testing to determine nitrogen (N) fertilizer needs for crops is not recommend since N can change forms or be lost from the soil.
