Soil testing can help determine what nutrients your soil needs

Lee Rouse  |  4/16/2018 8:36:02 PM

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“Despite all of our achievements, we owe our existence to a 6-inch layer of topsoil and the fact that it rains.” — Farm Equipment Association of Minnesota and South Dakota.

Soil is one of the most important factors to manage when growing fruits, vegetables, turf or ornamentals. Many factors of soil need to be managed, or at least kept a watchful eye on, in order to grow plants to their optimum capacity. These factors include soil texture, soiled tilth, organic matter, and finally, soil fertility.

Soil fertility is the most important of the factors to consider when setting out to manage your soil. It’s most often highlighted, partly because it's the factor which we have the most control over. Performing a soil test can help you determine what nutrients are in the soil. And when compared to a known crop or plant, the LSU AgCenter can make an accurate recommendation for fertilizers and amendments specific to your plant and your soil.

Oftentimes there is a slight miscommunication when referring to what the plants are growing in. It is typically for gardeners and companies to refer to anything in which a plant grows as soil. A soil consists of a combination of sand, silt and clay with some organic matter. However, a potting or gardening soil should more accurately be termed potting or gardening mediumbecause the content is primarily composed of organic matter. This may seem like splitting hairs, but it is very important to know the difference when having a soil test performed.

When taking a soil sample to test for fertility, it is important to indicate whether the material is a true soil or a soilless potting or gardening media. A true soil is one that contains sand, silt or clay and less than 20 percent organic matter. A native soil here in Louisiana has anywhere from 1 to 5 percent organic matter.

A gardening or potting media, on the other hand, is one that would typically be purchased from a garden center or nursery. Though these products are not true soils, many times they will have the term soil within the name. This gardening or potting media consists of 20 percent or more organic matter, so it’s not really “soil.”

Proper identification between soil and soilless media is important information to indicate when having soil test performed. This information determines which methods a lab will use when performing the soil test.

When taking a soil sample, it is important to pull multiple samples from a growing area and mix them together very well to form a composite sample. This composite sample will give a good indication of soil fertility of that particular growing area. It is always beneficial to pull multiple composite soil samples from two or more distinctly different gardening areas, such as lawns, flower beds and vegetables beds. Distinctly different could also be your front yard vs. your back yard or an elevated area vs. a depressed area.

Soil test results will provide you with invaluable information such as pH, nutrients, and soil texture information. Results also provide nitrogen, phosphorus and potassium recommendations, as well as recommendations for lime or sulfur to adjust the pH of the soil.

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