Going to the doctor on a routine basis, even if you don’t have symptoms, makes sense. It’s called a checkup. The doctor listens to your chest with a stethoscope, examines your ears and throat, and measures your vital signs. If checkups make sense for you, do they make sense for your corn and soybeans? They can’t talk, but you can listen and observe using diagnostic tools such as tissue tests.

“One of the best ways to monitor what’s going on nutritionally during the season is through tissue testing,” says Betsy Bower, an agronomist with Ceres Solutions. “It won’t answer all of your questions, and sometimes the results may seem hard to explain on the surface. But if you couple what you learn from tissue tests with other information, you can begin making more intelligent decisions about applying more inputs to capture maximum yield potential.”

If your goal is simply monitoring nutritional levels, Bower recommends sampling at three key times in corn. Take the first sample around the five-leaf stage, or V5. Pull another sample from the same area at V10 to V12, and a third sample early in the reproductive phase, from R1 to R3.

Should you see visible symptoms of what you suspect is a nutritional deficiency, you can pull a tissue sample anytime.

“Normally, then we would pull samples from areas which aren’t doing well and samples from areas which look normal,” Bower says. “We’re trying to determine if differences in nutritional makeup between the two areas might explain what we’re seeing.”

Test and tweak

Two things Bower looks for in tissue test results at all three key points in the season are the nitrogen-to-sulfur ratio and the nitrogen-to-potassium ratio. Most testing labs will break out these ratios for you, either in numbers, a bar graph or both.

“If the nitrogen-to-sulfur ratio is a bit wide early and sulfur values themselves are a bit low, adding sulfur to the growing crop might help, especially if it’s early in the season,” Bower says. “We also look at micronutrient values. If some are low, it’s an indication that adding them through a foliar application might help.”

Since many people who irrigate are also set up to apply fertilizer through irrigation during the season, some believe tissue testing is only helpful if you irrigate.

“Tissue testing can be helpful to anyone if you pay attention to the results,” Bower says. “There are ways to make effective applications in dryland fields, too, if results indicate more nutrients are needed.”

Tissue testing also pays for soybeans if your goal is monitoring crop performance and tweaking your soil fertility program over time, Bower believes. In soybeans, pull the first sample around the V3 to V5 vegetative stage, if possible. If not, begin at R1. According to the Purdue University Corn and Soybean Field Guide, at R1, there is an open flower at any node on the main stem.

Bower recommends sampling again at R3, when a pod at one of the four uppermost nodes on the main stem has a bean at least one-eighth inch long. It’s still possible to correct potential deficiencies. She also suggests sampling a final time at R5 to get a good read on macronutrient levels.