Gene-edited soil bacteria could become a third source of nitrogen for corn production

“To replace all synthetic nitrogen would certainly be something. Maybe in 100 years we’ll find microbes and genetic changes to get closer to that goal, but those microbes aren’t there yet. However, we have to start somewhere, and this work shows that nitrogen fixation has potential for corn,” said study co-author Connor Sible, an assistant professor in the Department of Crop Science, part of the College of Agricultural, Consumer and Environmental Sciences at Illinois.

Sible and his co-authors tested products from Pivot Bio called PROVEN and PROVEN® 40, which contain one or two species of soil bacteria, respectively, that can convert atmospheric nitrogen into forms available to plants. The edited versions increase the activity of a key gene involved in nitrogen fixation, making it more available to plants. When applied at planting, the bacteria colonize plant roots, delivering nutrients to where they are most needed.

The company claims that biologically fixed nitrogen can potentially replace the equivalent of up to 40 pounds per acre of fertilizer nitrogen.

“There is a lack of peer-reviewed published data to support this claim. There are also no studies evaluating the magnitude of nitrogen replacement values ​​and when in the growth cycle additional nitrogen accumulates,” said Logan Woodward, who completed the research as a postdoctoral fellow at Illinois. “Our goal was to fill these gaps in knowledge.”

Researchers applied the products at seed over three field seasons using standard corn agronomic practices, including nitrogen fertilizers at rates of 0, 40, 80, 120, or 200 pounds per acre. They then measured plant tissue nitrogen at V8 (eight fully collared leaves) and R1 (silk emergence), as well as grain yield at the end of each season. Dilution of plant and soil stable isotopic nitrogen showed that additional nitrogen uptake in inoculated plots occurred from the atmosphere, supplementing soil and fertilizer supplies.

Analysis showed that at all nitrogen fertilization rates, the inoculant increased vegetative corn growth, nitrogen accumulation, grain number and yield by an average of 2 bushels per acre. With moderate doses of nitrogen, yields increased by 4 bushels per acre. This was equivalent to 10-35 pounds of nitrogen per acre of fertilizer.

“The overall yield response has been positive but modest. The 35 pounds of fertilizer equivalent during early growth dropped to about 10 by the end of the season,” said senior study author Fred Bellow, professor of crop science. “Obviously, we still need to apply fertilizers. You need enough nitrogen to grow a happy and healthy plant because a healthy plant can produce the root sugars it needs to feed the microbes. Without nitrogen, the plant cannot support itself or inoculate microbes, so the efficiency is significantly reduced in the absence of a certain amount of nitrogen in the fertilizer.”

While the products as they currently exist cannot replace synthetic fertilizers, the research team believes the technology is promising and hopes it can be improved to provide even greater benefits. However, products can be useful in certain applications today.

“Every farm has areas of the field where the soil is not providing enough nitrogen, or the fertilizer has been lost or unavailable, so a microbial inoculant to provide a third source of nitrogen can help,” Sible said. “Sometimes corn fields get ‘insurance nitrogen,’ where an extra 20 pounds is added in case the year is prone to nitrogen losses. “Maybe a nitrogen-fixing inoculant can reduce the need for that extra 20 pounds, and that can have a big impact across all Corn Belt acres.”