Biological Nitrification Inhibition (BNI): Our Savior from Nitrogen Pollution?

 By Zara Haider

Courtesy of the University of Nebraska-Lincoln’s Institute of Agriculture and Natural Resources, a field of sorghum

Whether you are a home gardener who dreams of having a mystical flower garden or a large-scale vegetable farmer who is responsible for hundreds of acres of land, you use the same tool to help your plants grow faster: nitrogen fertilizer. 

Nitrogen fertilizer has been scientifically proven to quicken the maturity rate of plants. The glucose made from the process of photosynthesis requires nitrogen to convert it into essential amino acids for protein development.  In 2017, a research study conducted by Razaq, Zhang, et. al tested its effectiveness, along with phosphorus (P), by providing various concentrations of nitrogen (0g, 5,10g, 15g). They found that compared to the control group, plants given either 5-15g had greater height and root collar diameter. Though it is important to note that there is a “sweet spot” with nitrogen fertilizers. The same study found that 10g treatments resulted in the most change, with 10cm height and 5mm diameter difference compared to the second most developed plant.

Like water, nitrogen has its cycle: nitrification. Fertilizers often offer ammonia (NH3) or ammonium (NH4+), which through an ammonia/ammonium-oxidizing bacteria and archaea turns into nitrite (NO2-). Then, a nitrite-oxidizing bacterium turns into nitrate (NO3-). From there, a portion is used by the plant, and the rest undergoes the subsequent process: denitrification. Though a denitrifying bacterium, the remaining nitrate turns into nitrogen gas (N2) and is released into the atmosphere. 

          Courtesy of Wikimedia; diagram of the Nitrogen Cycle

In agricultural processes, crops are given a significant amount of nitrogen fertilizers, but most of its provided nutrients are utilized effectively and are lost to either the atmosphere or in the water as nitrates or nitrous oxide. So, on top of the nitrogen gas being released by plants at a normal rate, other forms of nitrogen are also. This is a point of concern known as nitrogen pollution 

Plants have what scientists call biological nitrification inhibition (BNI) or the plant’s ability to suppress the denitrifying process. In 2019, Dr. Nithaya Rajan –a Texas A&M [university] AgriLife Research crop physiologist in College Station– found that this property is the key to plants’ efficiency and the cessation of the consequential environmental effects: plants having a high BNI can produce less nitrogen pollution, produce crops faster with less fertilizer. Rajan chose the crop plant sorghum, a cheap cereal crop native to Africa, to test her hypothesis.  She created a project study called the “Innovative Sorghum-Based Production Systems with Biological Nitrification Inhibition Property to Enhance Sustainability of Agroecosystems” that was funded with half a million dollars via a sponsored program of the USDA (United States Department of Agriculture). 

A separate study funded by the same program explores the BNI properties of various genotypes of sorghums that are provided and overseen by the sorghum breeder Dr. William Rooney. The study collaborates with an expert on BNI, Dr. Guntur Sabbarao, from Japan International Research Center for Agricultural Sciences (JIRCAS), along with another similar entity.

Rajan’s project received advice and efforts from JIRCAS and announced to concentrate its efforts to study and test the effectiveness of the BNI properties in sorghum for the next two years. 

In 2021, Rajan’s group confirmed Rajan’s hypothesis and discovered that “BNI is a heritable trait,” which was quoted from Rooney. Dr. Okumoto–plant physiologist and associate professor in the Department of the Soil and Crop Sciences – found the specific gene combinations that maximize a sorghum’s BNI, which was used to create a model that predicts BNI susceptibility. This can be beneficial in breeding programs to produce “smart” sorghum crops of the highest efficiency. 

Despite the high achievement made by Rajan’s team, they still have work to do. They haven’t calculated the adjusted amount of fertilizer farmers can safely use on these new crops without suffering the risks of overfertilization of plants. Additionally, a member of Rajan’s team is working to confirm BNI’s negligible effects on the soil’s precious microbiome. 

This verification of the capabilities of BNI is huge for the future of agriculture production. It has the potential of reducing the sizable proportion of greenhouse gasses emitted by crops, as well as the amount and cost of fertilizer. 

Sources:

1. Bernhard, A. (2010). The Nitrogen Cycle: Processes, Players, and Human Impact. Nature Education Knowledge. https://www.nature.com/scitable/knowledge/library/the-nitrogen-cycle-processes-players-and-human-15644632/ 

2. Ledbetter, K. (2019, July 19). Texas A&M researchers to develop climate-smart sorghum with use of BNI. AgriLife Today. https://agrilifetoday.tamu.edu/2019/07/19/texas-am-researchers-to-develop-climate-smart-sorghum-bni/ 

3. Ledbetter, K. (2024, September 12). Texas A&M AgriLife researchers identify novel approach to minimize nitrogen loss in crops - AgriLife Today. AgriLife Today. https://agrilifetoday.tamu.edu/2024/09/12/texas-am-agrilife-researchers-identify-novel-approach-to-minimize-nitrogen-loss-in-crops/ 

4. Razaq, M., Zhang, P., Shen, H., & Salahuddin. (2017). Influence of nitrogen and phosphorous on the growth and root morphology of Acer mono. PLOS ONE, 12(2), e0171321. https://doi.org/10.1371/journal.pone.0171321