Knowing what nutrients are in your soil and what nutrients are needed is a basic step towards good plant health. Soil nutrient balance must be managed for best plant growth, according to LSU AgCenter horticulturist Dr. Tom Koske.

“Early winter is a great time to do a soil test,” Koske said, explaining that doing so now beats the spring rush and allows time to find and apply what is needed. For example, if lime is required to raise the soil pH, it must be applied several months before it is actually needed to support good spring growth. Lime takes several months to reduce soil acidity completely and may cause plant burning if applied when the weather is very warm.

A late-season soil test also can show how well you came through the past growing season. Test values should come out mid-range to show that your fertility program was adequate and not too strong or weak.

Too strong of a fertility program will cause a buildup of nutrients and a high or very high test result.

“A nutrient surplus is not like money in the bank,” Koske said, explaining, “A buildup actually can lead to growth problems or groundwater pollution.”

Too weak a program, on the other hand, registers low to very low test values. Low values indicate you had run out of good fertility before the end of the growing season and may have weakened the plants.

A routine LSU AgCenter soil test lists values for potassium, phosphorus, calcium, magnesium and pH among others. These major nutrients along with nitrogen fuel growth. Because nitrogen is so temporary, it’s not included in the soil test.

“We just advise on its use, based on soil type and crop,” Koske said.

If your soil is similar throughout the property, one sample from a 4- to 6-inch profile can be used to make recommendations for several plants. List all the plants for which you want fertilizer recommendations.

“Be crop-specific,” Koske said, “because just listing Bermuda grass, for example, could result in recommendations for a pasture, not a lawn.”

Soil samples may be brought to your local parish LSU AgCenter office or delivered to the LSU soil test lab in Sturgis Hall on the AgCenter campus in Baton Rouge. The charge is $7, and results can be e-mailed back to you. Go to http://www.lsuagcenter.com/stpal or contact your local county agent for more information.

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Contact: Tom Koske at (225) 578-2222 or tkoske@agcenter.lsu.edu 
Editor: Mark Claesgens at (225) 578-2939 or mclaesgens@agcenter.lsu.edu