Enhancing Plant Health and Crop Yield
Nitrogen-fixing bacteria are truly the marvels of the natural world. They convert atmospheric nitrogen gas into biologically available nitrogen. Some of these bacteria have even learned to collaborate with plants, settling inside their roots. This process, known as nitrogen fixation and root nodule formation, is essential for leguminous plants like soybeans and clover. Other nitrogen-fixing bacteria reside inside other plant tissues or outside the roots, contributing nitrogen that promotes plant growth and ultimately enhances crop yield.
A new study published in Agronomy for Sustainable Development sought to better understand the role of nitrogen-fixing bacteria in agriculture. Researchers analyzed data from peer-reviewed publications and 68 studies conducted across seven countries. They found that these bacteria can improve plant health and increase crop yield by up to 30%. This finding is significant, as it could have major implications for food security and sustainable agriculture.
The Importance of Nitrogen-Fixing Bacteria
Nitrogen is an essential element for all life on Earth. It is a critical component of DNA and proteins; plants use it to produce chlorophyll. Although nitrogen gas makes up 78% of the air we breathe, plants cannot use it in its gaseous form.
Bacteria in the Rhizobium genus are among the best-known nitrogen-fixing bacteria because they form root nodules with legumes. In these nodules, the plant provides sugar and protection from oxygen, which enhances the bacteria’s nitrogen fixation abilities. In turn, the bacteria convert nitrogen gas into ammonia, a form of nitrogen that plants can use. This relationship between Rhizobium and legumes is a prime example of symbiosis, though other, looser forms of relationships exist between nitrogen-fixing bacteria and plants.
In agricultural systems, nitrogen-fixing bacteria can be applied to crops as biofertilizers. These bacteria are integrated into the soil by coating seeds with liquid or peat-based powder Rhizobium inoculants (RI) or by treating the soil with granular or liquid inoculants. An alternative method is to treat the soil with synthetic nitrogen fertilizers (NF).
Researchers compared the effects of RI on common bean growth with those of NF. In some conditions, RI proved to be more effective. The study authors wrote, “Here we show for the first time that, under dry-season, no-tillage systems, and in soils with high organic matter content, RI can outperform NF and have potentially positive effects on yield.”
The Role of Nitrogen-Fixing Bacteria in Reducing Synthetic Fertilizer Use
Beyond increasing yield, nitrogen-fixing bacteria can also play a crucial role in reducing agriculture’s reliance on synthetic fertilizers. The Haber-Bosch process, which converts hydrogen and nitrogen into ammonia for synthetic fertilizer, requires large amounts of energy and has significant environmental impacts. In contrast, biofertilizers use readily available organic elements, reducing the risk of excessive use.
“These organisms have always coexisted with plants, so we’re reintroducing something to the soil that has a known history,” says Dr. Roland Wilhelm, Assistant Professor in the Department of Agronomy at Purdue University. “Synthetic fertilizers became heavily used during the Green Revolution in the 1950s and 60s, and when misused, nitrogen can leach into our waterways, causing pollution or entering the atmosphere as a potent greenhouse gas (N2O).”
Dr. Wilhelm adds, “With nitrogen-fixing bacteria, plants themselves support the microbes, and this means very little excess nitrogen is produced—certainly not to the point where it becomes a pollutant.”
The key difference between using plant-growth-promoting bacteria and synthetic fertilizers is that bacterial use encourages a natural and active process. Wilhelm explains, “Plants send signals to the environment, and microbes respond in harmony to provide plants with what they need. Plants actively take up nitrogen from microbes, and this is an evolutionary journey that shaped plants long before humans started providing nitrogen artificially.”
Challenges to Consider
Nitrogen-fixing bacteria are found in constantly changing environments. Climate, organic matter in the soil, and farming practices can all impact how effectively these bacteria function. This means there is no one-size-fits-all approach to their use.
So, how can farmers know what their soil microbiome looks like and how to make use of this information?
This is where soil microbiome testing companies like SoilBiom come into play. Through these innovations in soil testing, farmers, agronomists, and soil health experts can analyze the microbiome of the soil to understand its structure.
A study conducted by a group of researchers at Cornell University, including Dr. Wilhelm, found that some aspects of the soil microbiome can predict soil health metrics and characteristics. The authors wrote, “Our study lays the groundwork for the development of scalable technologies for microbiome-based diagnostics in assessing soil health.”
As more research is conducted, the goal of soil microbiome testing in agriculture is to diagnose and assess soil according to defined indicators of soil health. For example, suppose a farmer plants nitrogen-fixing bacteria-coated seeds. In that case, they could test the effect of this planting on the soil microbiome and, if the soil looks good based on defined parameters, potentially reduce future fertilizer applications, saving costs.
A Better Understanding of Soil (and Human) Health
The focus on nitrogen-fixing bacteria and other plant-growth-promoting bacteria comes at a time when more scientists are uncovering the importance of bacteria and unicellular organisms in all aspects of life. All living things, including humans, have evolved in a world dominated by prokaryotic life forms such as bacteria and unicellular organisms. Plants and humans alike need microorganisms to be healthy.
Further research into bacteria and their role in healthy systems will continue to benefit our food systems and overall health.
Nitrogen-fixing bacteria are crucial in this paradigm shift, as they biologically make nitrogen biologically available in a process that requires far less energy than the Haber-Bosch method. This process occurs in the soil around us. All that is required is ensuring the right conditions for cooperation between the plants and microbes.
Rather than asking, “How can we manipulate the soil to grow more plants?” the real question should be, “How can we support the organisms in the soil to grow healthier plants?”