Kansas City, MO. — The role of biological nitrogen fixation (BNF) in non-legume crops such as cereals as an alternate source to chemical fertilizers has been a longtime goal in science and industry. Efforts in research and development of BNF in cereals still have not resulted in high enough Nitrogen (N) generation to be a total replacement for chemical fertilizers. However, recent research indicates BNF can contribute up to 30 percent of N requirement of a corn crop. 

BNF is a natural process by which atmospheric nitrogen is converted into ammonia or related compounds by microorganisms known as diazotrophs. This natural mechanism has many potential benefits for the environment and economics. Examples of N-fixing bacteria include species of Rhizobium, Azospirillum, Bacillus, Klebsiella and Gluconacetobacter.

"Historical reports have shown relevant BNF from natural sources in certain non-legume crops such as sugarcane or rice," says Ignacio Colonna, AgriThority Global Director, Science & Technology. "BNF supplies a large amount of natural nitrogen into cultivated agricultural systems, particularly in legume crops (alfalfa, clover, and soybean) through symbiotic N-fixing Rhizobia that are both naturally present in the soil and applied to seeds or soil as external inputs." 

In recent years, new bacterial strains have been discovered and developed through a range of biotechnological approaches. Some of these strains show a significant capacity to enhance plant growth in cereals through N fixation. Applied both as in-furrow application or seed treatment, the bacteria strains have variable responses in non-legume crops such as corn, lettuce, tomato, and strawberry. 

"In the last five years, AgriThority conducted more than 100 greenhouse and field studies in the U.S. and Argentina to evaluate selected wild-type and genetically edited strains of non-symbiotic diazotrophic and plant-associated bacteria," Colonna says. "The best performing strains in these corn trials have shown a replacement of chemical nitrogen sources from BNF in amounts equivalent to 20-30 percent of total crop fertilizer requirements in certain environments. We are evaluating early generations of a large pipeline of experimental strains, so we expect to see steep changes in these contributions in the next five years. We also are excited about evaluating these technologies in other grass species like wheat and barley."  

Learnings from statistical analysis of these large trial data sets allowed the AgriThority research team to refine general guidelines in experimental design for BNF studies. For example, for products aiming at a N fertilizer replacement of approximately 15 percent, a minimum of 12-15 locations of small plot replicated trials are required for a statistically robust evaluation of treatment effects. A minimum of 8-10 trials are required to detect the true response of BNF bacteria with approximately 25 percent replacement amount at reasonable thresholds of statistical power and type I errors. 

"While these guidelines need to be adjusted to each geography, they provide us with a good reference to maximize chances of obtaining valuable information from each research project," Colonna says. "Adapting your experimental design to the expected treatment responses is critical for an effective testing program."

Also, careful selection of experimental sites and management of crop chemical fertilizers proved critical in BNF studies, as crop response to BNF bacteria was clearer at moderate N soil contents compared to very low or high N soils. 

"Testing at very low nutrient contents can be a challenge, as it usually compromises experimental error through higher within-trial heterogeneity," Colonna says. "A realistic assessment of these technologies requires a balanced weight of these environments in the overall experiment network. A clear breakout of results can properly quantify the effects across different environments to determine viability in each crop."