Suppose you see leaf discoloration in corn or soybeans. Will tissue tests help this late in the year? Should you sample soils, too?
“Once visual symptoms appear, often the yield potential has been reduced,” says Jamie Bultemeier, with A&L Great Lakes Labs, Fort Wayne. He’s an Indiana certified crop adviser.
“Tissue testing allows for earlier detection and reduces the chance of a missed diagnosis of similar visual symptomology,” he adds. Plus, it’s possible that a nutrient is only marginally deficient and won’t develop visual symptomology but will still impact yield.
“To gain the maximum benefit to tissue sampling, be sure to take a soil sample at the same locations,” Bultemeier says. “A tissue sample is only a snapshot in time.”
Bultemeier adds that a tissue test may identify that a given nutrient is low but doesn’t answer why. Also, a tissue test may show adequate levels, but it can’t estimate the soil reserves of a given nutrient to support the plant through the remaining growing season. A soil test in conjunction with a tissue test can answer these questions and bring greater interpretative value to the tissue test, he explains.
Suppose the tissue test is low, but the soil test is not, he says. Then the plant is unable to access the nutrient, and additional soil-applied fertilizer will not be effective.
“If both the soil test and tissue test are low, then addressing soil fertility levels should be the focus of future management,” he says.
For all vegetative growth stages in corn, collect the top-most leaf with a collar, Bultemeier says. Once the ear shoot is identifiable, collect the leaf directly under the ear. Collect 12 to 15 leaves.
In soybeans, he recommends collecting tissue samples in midvegetative stage and then again at R3. Both times, collect the most recently matured leaves from 25 plants. You’ll find them three to four nodes from the top of the plant, he says. These leaves need to be full size and the same color as leaves below them. More than one sampling date can help pinpoint when a shortage begins to develop, he says.
Marty Park with Great Lakes Seed Service, Rensselaer, Ind., also a CCA, says that in corn, look for nitrogen and potash deficiencies this time of year. Nitrogen shows up as firing on the leaves starting at the bottom of the plant and moving up. Individual leaves have the inverted “V” that goes from the edge of the leaf to the midrib.
Potash deficiency has shown up recently along edges of fields, he adds. Look for yellowing along leaf margins starting at the tip on the lower plant. Tissue turns brown.
In soybeans, potash deficiency shows up as yellow leaf edges that look like they’re dying on the upper leaves, Park says. Manganese deficiency shows up as pale yellow to white interveinal areas while veins remain green.
Tissue testing can confirm these deficiencies, but it might be too late to react for this crop season, he believes. If you pull tissue samples, pull soil samples in the same spots.
“I like to pull a ‘good’ tissue sample and soil sample as well as a ‘bad’ tissue sample and soil sample in the same area,” he says. “That allows me to compare what’s in the soil as well as the plant in the ‘good’ and ‘bad’ areas.”