An alfalfa plant is a lot like an iceberg, says Roger Elliott. The most important part is hidden.
“Alfalfa is a root-driven crop,” says Elliott, an Evansville, MN, dairyman. “What's under the surface controls everything.”
Elliott and Del Glanzer, his crop consultant, periodically dig 7'-deep pits in alfalfa fields to examine the roots and the soil around them.
“It gives you a whole new insight into what's going on underground,” says Elliott. “And that can help you do a better job of tillage, fertilization and everything else.”
Pits told Elliott, for example, that his farm has an 8-9" deep hardpan. The hard layer was preventing moisture from moving down in wet periods and up in dry periods. Now he breaks it up with deep tillage prior to planting corn. That has increased alfalfa yields by improving water movement and reducing the incidence of disease, he says.
Pits also can reveal the location and severity of yield-robbing compaction. Every grower has the problem, says Elliott. By examining the soil profile, you can decide if you can solve the problem with tillage.
Elliott has learned that alfalfa roots often grow less than 2' deep in poor-yielding parts of fields. In healthy areas, they're sometimes more than 7' deep. But he and Glanzer don't yet know the root characteristics that lead to highest yields.
“We see differences, but we don't know what we want yet,” says Elliott.
He hires a backhoe operator to dig pits, usually in older stands. But he also has a less-disruptive 1'-square by 40"-long probe to use in younger stands. He hires the backhoe operator to pound it into the ground and pull it out, but figures a tractor and front-end loader would work.
He made the 3/8"-steel probe a few years ago when testing coated alfalfa seed for CelPril. He wanted to find out why plants from coated seed grew better than those from uncoated seed. Now he uses it when he has a serious question about a field.
“It gives me an opportunity to really look at the plant and soil to try and answer the question,” he says.
The probe doesn't replace pits, though. Glanzer thinks every grower should dig pits to study alfalfa's root system and the soil profile. Have a soil and water specialist or crop consultant there to educate you.
“If there's a problem in the top growth, it's probably due to the roots,” says Glanzer. “If you don't know what good, healthy alfalfa roots look like, how do you know when you've got them?”