News You Can Use For June 2004
Plants produce best in a location with the proper fertility. LSU AgCenter horticulturist Dr. Tom Koske says some plants are heavy feeders, some light feeders and some are in between.
"If you feed a light feeder as a heavy feeder, it does not mean you will get more flowers or fruit," Koske notes, explaining, "In fact, you usually get less or maybe none at all." The horticulturist examines three basic areas of soil fertility - soil nutrients, pH and organic matter.
"Twelve to 14 soil nutrients are considered essential to most plants, 14 if you consider nickel and chlorine," Koske says. The primary nutrients of nitrogen, phosphorus and potassium are used in large quantities and are the three main numbers found on fertilizer bags. Also used in large amounts are the secondary nutrients of calcium, magnesium and sulphur.
"We often don’t directly supply these, but sometimes we do when we add lime," the horticulturist says.
Other soil nutrients are used in small quantities and are referred to as micronutrients. Although needed in small quantities, their availability is very important for normal growth.
All of the soil nutrients are required at the correct levels and in the correct forms for good availability to the plants.
"This is one place where the soil pH, or measure of soil acidity, comes into the picture," the Koske says, explaining, "The soil pH levels can greatly affect the form and thus the plant availability of a soil nutrient."
Most soil nutrients are very available between pH 6 and 7, a desirable range for most plants. Several nutrients get very available at higher pH and several get very available at pH of 5 to 6. These high availabilities then may produce a nutrient toxicity to sensitive plants. Some plants tolerate higher pH and some acid lovers thrive in pH of 5 to 5.5.
Organic matter (OM) is the third factor in soil fertility. It has a stabilizing and enhancing effect. OM doesn’t always supply nutrients organically, although the fresher materials may. OM usually mellows the soil, making it more friable and workable. The OM can help stabilize soil pH, but it is mainly known for its nutrient-storing capacity.
The nutrients that go through the soil can be held on the OM for later exchanges to plant roots. Too much OM may produce a soil that is too rich for certain crops, so once again, more isn’t always better. Good soil test levels of OM are generally 2 percent to 5 percent for true soil.
All these levels and combinations should be considered for a crop, and the best combination should be offered for best growth and fruiting.
"A good way to figure out what you have and what is needed is the laboratory soil test," Koske says. The LSU AgCenter routine soil test analyzes pH, phosphorus, potassium, calcium, magnesium, sodium (salt) and texture. List a crop or two and the fertilizer recommendations, and any required liming, etc. will be listed with the results. The soil testing Web site address is www.lsuagcenter.com/stpal for more information.
For related topics, look for Gardening and Get It Growing links in the Feature section of the LSU AgCenter Web site: www.lsuagcenter.com. Additional yard and garden topics are available from an extension agent in your parish LSU AgCenter office.
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On the Internet: LSU AgCenter: http://www.lsuagcenter.com/
On the Internet: Soil testing lab www.lsuagcenter.com/stpal.
On the Internet: www.louisianalawnandgarden.org.
Source: Tom Koske (225) 578-2222, or tkoske@agcenter.lsu.edu.