If corn was ever jealous of soybean's relationship with nitrogen-fixing bacteria, advancements in gene editing could one day even the playing field. A recent study from the University of Illinois Urbana-Champaign shows that gene-edited bacteria can supply the equivalent of 35 pounds of nitrogen from the air during early corn growth, which may reduce the crop's reliance on nitrogen fertilizer.
- Lauren Quinn
"To replace all synthetic nitrogen would certainly be something. Maybe 100 years from now we will have found the microbes and genetic tweaks to get close to that goal, but these microbes are not there yet. However, we have to start somewhere, and this work demonstrates nitrogen-fixation for corn has potential," said study co-author Connor Sible, research assistant professor in the Department of Crop Sciences, 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 includes one or two species of soil bacteria, respectively, that can turn atmospheric nitrogen into plant-available forms. The edited versions boost the activity of a key gene involved in nitrogen fixation, making more of it available to plants. When applied at planting, the bacteria colonize plant roots, delivering the nutrient where it is needed most.
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 is also no research estimating the magnitude of nitrogen replacement values and when in the growth cycle that additional nitrogen is accumulated," said Logan Woodward, who completed the study as a doctoral student at Illinois. "Our objective was to fill those knowledge gaps."
The researchers applied the products at planting during three field seasons using standard agronomic practices for corn, including nitrogen fertilizer at 0, 40, 80, 120, or 200 pounds per acre. They then measured nitrogen in plant tissues at the V8 stage (eight fully-collared leaves) and at R1 (silk emergence), as well as grain yield at the end of each season. The dilution of plant and soil stable isotopic nitrogen showed that additional nitrogen uptake in the inoculated plots was from the atmosphere, supplementing the soil and fertilizer supply.
The analysis showed that, across all nitrogen fertilizer rates, the inoculant increased corn vegetative growth, nitrogen accumulation, kernel number, and yield by 2 bushels per acre on average. At the moderate nitrogen rates, yield was up by 4 bushels per acre. This was equivalent to 10-35 pounds of nitrogen per acre of fertilizer.
"The overall yield response was positive, but modest. The 35 pounds of fertilizer equivalent during early growth was down to about 10 by season's end," said senior study author Fred Below, professor in crop sciences. "Clearly, there is still a need to fertilize. You need enough nitrogen to build a happy and healthy plant, as a healthy plant can then produce the root sugars needed to feed the microbes. Without nitrogen, the plant cannot support itself nor the inoculated microbes, so the efficacy is quite diminished in the absence of some fertilizer nitrogen."
While the products as they are now cannot replace synthetic fertilizers, the research team thinks the technology shows promise and hopes it can be improved to deliver even greater benefits. Still, the products could be useful in certain applications today.
"Every farm has areas of the field where the soil does not provide enough nitrogen or the fertilizer was lost or unavailable, so a microbial inoculant to provide a third source of nitrogen could help," Sible said. "Sometimes corn fields receive 'insurance nitrogen' where an extra 20 pounds is supplied in case it is a year prone to nitrogen loss. Perhaps a nitrogen-fixing inoculant can reduce the need for those extra 20 pounds, and this could have a large impact when summed across all Corn Belt acres."
The study, "Soil inoculation with nitrogen-fixing bacteria to supplement maize fertilizer need," is published in Agronomy Journal [DOI: 10.1002/agj2.21729]. Authors include Logan Woodward, Connor Sible, Juliann Seebauer, and Fred Below. The research was supported by the USDA National Institute of Food and Agriculture.
