When an agronomist visits a field to diagnose a problem, it’s not unlike a doctor attempting to uncover the source of a patient’s discomfort.
Let’s use, as an example, the case of “tall corn, short corn” syndrome, an issue facing many farmers finding patches of corn several inches taller (or shorter) than others.
Like any doctor of medicine, a good crop doctor needs to take a temperature. That’s done with a soil penetrometer, which measures soil compaction by calculating resistance per square inch. In good conditions, there will only be about 200 pounds of resistance per square inch. This tool can help diagnose what may be causing variances in corn height. If you have compaction that means the soil particles are so tightly compressed that pore space is limited, reducing root access to air and water. That’s a big deal, and may be the reason the short corn hasn’t reached desired height.
But a good doctor doesn’t automatically decide a fever is the flu. For a full diagnosis, you need multiple data points. You’ll want to grab a soil probe and take soil samples. You will want to take a good, composite soil sample in both tall corn and short corn areas.
Every once in a while, your doctor has to draw blood to get a current snapshot of your health. Similar to a blood test, a tissue sample can help you figure out if a corn plant is getting everything it needs. Let’s say we’re talking about 4-inch corn and 8-inch corn: You’ll want to collect at least 10 plants each from both the short corn area and the tall corn area. You’ll cut off the entire plant at the surface of the soil.
Don’t forget — you need to have a proper container to transport your sample. Preferably, that’s a paper bag that you obtained from the laboratory. Along with that bag come some instructions that can be helpful. (Such as how much of the plant, and how many plants, to take.) You’ll also want to make sure you’re not taking a sample after a hard rain, when soil has washed up onto the leaves and can contaminate the sample. If you don’t have a choice, try to shake off as much of the soil as possible.
When those tissue sample results come in, you will be able to make a comparison. Look at what the differences are between the two, and figure out what the tall corn is getting that the short corn is not. It’s a really solid way of diagnosing problems in tall corn, short corn syndrome.
Another tool a good crop doctor should have is a SPAD® meter. A SPAD® meter measures the intensity of the chlorophyll. When corn is waist high, a SPAD® meter is very good at determining if a rescue nitrogen application is needed.
While it might seem simple, even the most seasoned agronomists find there are plenty of mistakes to be made diagnosing plant problems. But the most prevalent error is overreliance on one diagnostic tool. After all, your doctor uses more than just a stethoscope.