Foliar Testing Tells the True Story of Plant Nutrition

Accurate leaf sampling produces accurate results, saving money and maximizing yields.

Testing for nutrient levels is a process vegetable growers need to undertake to ensure a healthy crop. While the nutrient content of the soil needs to be determined, it also is necessary for growers to conduct foliar testing to find out exactly what is being taken up by the plant.

When should testing occur? According to Tim Coolong, assistant professor and Extension vegetable specialist in the Department of Horticulture at the University of Kentucky, at minimum, soil tests should be conducted in the fall for the next growing season. He also says it is a good idea to test the soil during the growing season as well.

“It can be helpful to sample during the season to determine how your fertility program is impacting your crops,” Coolong explains. “Many times, soil samples taken from in the planting row, under plastic mulch, can be very different than what is observed after all the plastic is removed and prepped for winter. Sampling during the season, in-row, will help tell you what your plant is actually experiencing.”

To get a complete reading on the health of the crop, however, plant leaves must be tested, too. By testing leaves, growers can determine if there is a nutrient competition issue.

For example, Coolong says a grower may have high potassium on a soil test, but also have high magnesium. “Often the magnesium can compete with potassium for uptake by the plant,” he explains. “Without leaf samples you don’t have a complete understanding of what is going on. However, it is also important to keep in mind that a good sampling technique is required. Without proper sampling your results may be off, and inaccurate results can be worse than no results at all. For sampling guidelines, contact the particular lab you plan on sending your samples to.”

Selecting Leaf Samples

Proper sampling also includes choosing the right leaves. Coolong says it is important to combine leaves from the same field to avoid variation issues, but combining leaves from extremely different plots or from sick and healthy plants will provide the grower with no valid information. “It simply might average the good and bad so you have no idea what is going on,” he explains. “In that case, it would just be a waste of money.”

Coolong adds that growers need to pay attention to the age of the leaves, as well. For example, a grower may have a nutrient deficiency in old leaves but only samples the newest, healthy ones. “Rarely will that tell you what is actually wrong,” he says. “If you have a deficient plant or plants be sure to send those in separately.”

Cost-saving Tactics

Virtually everything that has to do with crop production revolves around the soil and having healthy plants. Understanding how various fertilizers impact soil properties such as pH and vice-versa can really help growers become more profitable by saving money on fertilizers and producing better yields, says Coolong. “Even understanding the relative availability of different nutrients during the growing season can help growers reduce unnecessary applications of fertilizers,” he adds.

Coolong’s take-home message to growers is to pay attention to which leaves they sample in order to get an accurate reading. “If you are going to spend the money, be sure you are sampling correctly and following the appropriate guidelines,” he concludes. “If you sample poorly you are simply wasting money.”

Once you have an accurate nutrient analysis, you can decide what inputs to use, knowing you are delivering only what is needed. KeyPlex offers a wide range of products designed for crops from tomatoes, potatoes, carrots, cole crops and more.

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