June 8, 2020
A doctor listens to your lungs, heart and other organs with a stethoscope. Plants don’t make sounds, but they can display visual symptoms. However, if you really want to “listen” to what’s going on inside a plant, Andrew Schmidt believes tissue testing comes in handy.
“Some people only use it if they’re trying to diagnose problems,” says Schmidt, an agronomist with WinField United, covering Missouri and eastern Kansas. “We see value in routine tissue sampling at key stages.
“The information you get back will tell you what’s going on inside the plant. It’s a snapshot of what nutrients are getting into the plant at that point in time.
“In some cases, you can apply nutrients and bump up yield this season. Other times, what you learn may help you tweak soil fertility management for next season.”
If you’re only pulling tissue samples three times in corn, Schmidt suggests the V5 to V6 stage, from V8 to V10, and during silking and pollination.
“The five- to six-leaf stage is important because plants make decisions about ear girth size,” he says. “You’re checking for essential nutrients, both macronutrients and micronutrients.”
What you learn about nitrogen content at both early growth stages can be important, he says. If you’ve suffered significant nitrogen losses, you may already see visible signs. But if nitrogen content is borderline, it may show up in tissue testing, even if you aren’t seeing visible symptoms yet.
Nitrogen is important for the grand growth stage, which starts around V8 to V10, the agronomist says. But it’s also key once reproduction starts. If you pick up indications that nitrogen is borderline through tissue sampling at early testing times, you may choose to add more nitrogen. High-clearance equipment makes that convenient today, he notes.
“What you’re looking for when you pull tissue samples at silking is information on your whole management program,” Schmidt says. “What you learn may help you adjust for next season.”
Besides nitrogen, the nutrients that show up lacking in corn most often are zinc and boron, he says. Sulfur deficiencies also show up in some areas.
Soybean tissue tests
There are two critical times to pull tissue samples in soybeans, Schmidt says. “You want to know what’s going on at V4 to V6, in the heart of the vegetative stage,” he says. “Then you want to come back in the early reproductive stages, at R2 to R3.”
Many people think tissue testing primarily helps pick up micronutrient issues in soybeans. The one that’s typically borderline for soybeans on some soils in Schmidt’s geography and in the eastern Corn Belt is manganese. But potassium, a macronutrient, shows up borderline or deficient in a surprising number of tissue samples.
“Potassium is a key nutrient for soybeans, and they remove lots of it,” Schmidt says. “We can often pick up shortages in tissue sampling before symptoms appear.” Typical symptoms of potassium deficiency include browning or yellowing on the edge of leaves. Sulfur sometimes shows up as borderline or deficient as well.
“The goal is to determine what nutrients are in plants,” he says. “If something is in short supply, perhaps you can add it then. If not, you can plan for the next season.”
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