EWING, Ill. — Legumes have long been known to fix nitrogen. But whether that nitrogen is transferred to the field and made available to future crops is a question that begs an answer. That answer may come soon.
New varieties bred to enhance nitrogen production, and innovative management practices aimed at keeping the plants on the field late into the spring, could reduce the need for other nitrogen sources.
“There are some clovers out there that are probably better for nitrogen fixation than others,” said Marc Lamczyk, University of Illinois Extension crop systems educator.
That may be an understatement.
A recent trial at the Ewing Demonstration Center showed that a new variety added 269 pounds of nitrogen per acre over a period of 6½ months. Dixie crimson clover, planted as a control, added only 14 pounds per acre.
Lamczyk and fellow Extension educator Nathan Johanning are studying the benefits of the patented balansa clover variety named FIXatioN, developed by the seed company Grassland Oregon
The numbers achieved at Ewing are eye-popping, but they are not unusual, according to Risa Demasi, co-founder of the seed company, based in Salem, Ore. She points to another trial in Richland, Iowa, in which measured nitrogen was as high as 340 pounds per acre.
“We need to replicate that before we hang our hat on those numbers,” she said. “They were pretty wild numbers. The question is when is that nitrogen available for the next crop, and for how long.”
The company bred cold tolerance into the Mediterranean-based plant to produce the patented variety.
“Those are really crazy numbers,” Demasi said. “… We’re not touting those 300-plus numbers. We’re trying to be very conservative.”
One researcher is developing a nitrogen calculator that may provide some answers. University of Georgia agronomist Julia Gaskin has been working on the system, in which samples are taken of cover crops in the field and nitrogen is measured, along with carbohydrates, cellulose and lignin. The latter three substances tell how quickly the nitrogen may be released.
“We can predict these nitrogen credits or debits, and graph on when that nitrogen will be released,” Gaskin said. “The graph is really nice because it can help the farmer say, for instance, that if he takes a nitrogen credit, maybe he should wait until sidedress to apply his fertilizer. It gives them a way to better visualize some of the options in terms of nitrogen management and help them reduce inputs. And there are ancillary environmental benefits.”
Gaskin prefers a mixed stand of legumes and grasses, largely because a stand of pure legumes releases most of its nitrogen about the first month after it is killed.
“As a caveat, our conditions are a lot hotter down here,” she said. “But we really like grain-legume mixtures. That slows down the nitrogen uptake. A grain is adding more carbon into that system; that slows it down and spreads it out.”
Among other things, the researchers at Ewing Field hope to determine the ideal time to plant and terminate FIXatioN.
“The biomass on this balansa was unreal. We had trouble killing it,” Lamczyk said. “We maybe should have tried to kill it before we planted. We had trouble with no-till coulters cutting through this stuff. We eventually did get it killed, but it was quite a challenge.”
Next year they will consider either killing it earlier or planting the cash crop into it and killing it afterward, when the stems become more brittle.