Soil Tests Dig Deep to Improve Plant Health
By Kyle Peveto, LSU AgCenter
Research associate Lauren Liuzza weights soil samples in the LSU AgCenter Soil Testing and Plant Analysis Lab. Photo by Kyle Peveto/LSU AgCenter
BATON ROUGE, La. — Every day, LSU AgCenter extension agents see failing plants, trees or grasses brought to them in search of a fix.
“The plant is just sitting there,” said Lee Rouse, LSU AgCenter horticulture agent in East Baton Rouge Parish. “It’s not growing. It’s not flowering. It’s not fruiting. It’s not performing some task it was meant to do. What is wrong?”
“Typically, the first question is, ‘Have you had a soil test?’” Rouse said.
Soil tests by the LSU AgCenter Soil Testing and Plant Analysis Lab on the LSU campus analyze the soil nutrient content and whether it is acidic or alkaline so experts can recommend any fertilizers and treatments needed to grow certain plants, trees or grasses.
The analysis can pinpoint the exact needs of the soil, Rouse said, so instead of treating plants with a general fertilizer that provides a broad range of nutrients, a gardener can use what is needed.
“You may need those nutrients,” Rouse said. “You may not. You just don’t know until you get a soil test.”
A group of soils is dried, ground and prepared for further testing at the LSU AgCenter Soil Testing and Plant Analysis Lab. Photo by Kyle Peveto/LSU AgCenter
As summer ends, Rouse recommends testing soil in preparation for fall gardens and the tree and shrub planting season coming in December. Although some amendments added to the soil will become available to plants quickly, others need months. Elemental sulfur, for example, takes two to four months to become active, Rouse said.
“Now is a great time to get your soil tested,” Rouse said. “You have enough time to pull the tests, send them off and get the results and make the necessary changes.”
Soil tests can be completed in a week to 10 days. Sampling kits available at nursery retailers and parish extension offices across the state include everything needed to mail the test to the lab — an information form, three plastic bags for soil samples and a prepaid U.S. Postal Service shipping box. Routine tests cost $10 plus $6 in postage, which is paid to the lab.
On the soil test request form, clients list what they wish to grow in the soil being tested, and in return, they receive instructions on how to prepare for planting.
Some of the samples sent to the lab will say something like “Can you tell me what’s good to grow in this soil?” said Michael Breithaupt, AgCenter Soil Testing and Plant Analysis Lab manager, who noted that the lab isn’t able to provide that level of analysis for each customer. “We want to know what you want to grow, and we will tell you what to amend for it,” he said.
While springtime between Mardi Gras and May might be the lab’s peak season, every day is busy, Breithaupt said.
On the first floor of Sturgis Hall at LSU, workers empty dozens of boxes onto a table in the back of the lab each morning and remove small plastic bags of soil. To begin testing, every sample is given a code and then sent through a dryer and a grinder.
Before the soil is analyzed with high-tech equipment like the pH analyzer and the spectrometer, lab technicians rub a bit of the dried, rewetted and ground soil between their fingers. Machines can’t quite replicate the sense of touch for the texture test, Breithaupt said.
Feeling the texture helps them recommend fertilizers to the client.
“Clay soil will hold onto the fertilizer, but sandy stuff will let it drain,” Breithaupt said.
Additional tests can delve deeper into other plant problems. An optional soil test can analyze the levels of salts, organic matter and a variety of elements in the soil. A water test can determine the mineral composition of irrigation water and its pH level, and a separate plant tissue test analyzes the stems, leaves and roots of a plant.
Last year the soil lab performed 18,005 soil tests for clients that included home gardeners, farmers, nurseries, turf growers and researchers. Hunters and game land managers growing food plots designed to attract deer account for the largest single group with at least 35 percent of the tests, Breithaupt said.
Once completed and sent to customers, routine reports from the lab give basic advice. For example, they may tell how many pounds of sulfur to add for every 100 square feet to a soil with a high pH so azaleas or other acid-loving shrubs can grow, or they might recommend three applications of potash to a field for alfalfa or a similar annual legume.
Each client’s local AgCenter extension office also receives a copy of the test results. AgCenter extension agents can help answer any questions about the tests, Rouse said.
“The best piece of information on a soil test is your county agent’s phone number,” Rouse said.
The Soil Testing and Plant Analysis Lab recommends these tips for collecting a soil sample:
— Dig straight down a few inches when gathering soil. Do not scoop. “You always want to get to the root zone,” Breithaupt said. “That is the top layer to the roots.”
— Get a soil sample every two to three acres on larger tracts of land. For flower beds in smaller lots, take samples from individual beds because the soil in each bed may differ. “When you are in the city, people bring in soil all the time,” Breithaupt said. “This flower bed might be totally different from this flower bed.”
— Samples must be free of any amendments — no fertilizers or lime. “Either one of those or both of them, your data is skewed,” Breithaupt said. Sometimes gardeners don’t realize that popular treatments, such as Miracle-Gro and Scott’s Turfbuilder Weed and Feed, are fertilizers, he said. If either has been applied recently, give it time. “Wait a few months and let it work its way through the system, then send it in,” he said.
— For each sample, combine two or three spots from the area you wish to be tested so oddities from one scoop of soil do not overly affect the test. “Take here, here and here and put it in a bucket, and that will combine that area,” Breithaupt said.
— Get plenty of soil. “There’s no such thing as too much sample,” Breithaupt said. “Fill those bags up.”