Texas A&M AgriLife researchers identify novel approach to minimize nitrogen loss in crops

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Biological nitrification inhibition trait in sorghum may allow reduced fertilizer use and greenhouse gas emissions

By Kay Ledbetter

While agriculture producers apply nitrogen fertilizer to supply nutrients to their crops, they can’t always keep those nutrients in the soil for maximum efficiency, often losing them into the atmosphere or water supply as nitrates and nitrous oxide.

A Texas A&M AgriLife Research team is working to find crop varieties, starting with sorghum, that will minimize that escaped nitrogen, thus reducing input costs for farmers and greenhouse gas emissions into the atmosphere.

The project is led by Nithya Rajan, Ph.D., recently named director of the Center for Greenhouse Gas Management in Agriculture and Forestry. Rajan is an AgriLife Research crop physiologist and professor of agronomy and agroecology in the Texas A&M College of Agriculture and Life Sciences Department of Soil and Crop Sciences.

Five years ago, Rajan initiated the study, “Innovative Sorghum-Based Production Systems with Biological Nitrification Inhibition Property to Enhance Sustainability of Agroecosystems,” funded by the Agriculture and Food Research Initiative – Foundational and Applied Science Program of the U.S. Department of Agriculture National Institute for Food and Agriculture, USDA-NIFA.

She and her team now have results they say are promising in developing a trait that is good for the plant, the producer and the planet.

“The BNI trait will suppress nitrification, a microbial process that converts fertilizer-derived ammonium in the soil to nitrate, and not allow it to escape as nitrates in water or nitrous oxide as a greenhouse gas.”

Nitrification, denitrification and biological nitrification inhibition

Nitrification and subsequent denitrification activities promote nitrogen loss from agricultural fields and largely are the underlying reason for low nitrogen-use efficiency in most field crops and the emission of nitrous oxide, a highly potent greenhouse gas, Rajan said.

In today’s farming practices, producers must pay extra for fertilizer with a nitrification inhibitor to keep the fertilizer they applied in place.

However, it is known that some plants can suppress nitrification by releasing inhibitors from their roots, a property known as biological nitrification inhibition, BNI, she said. The BNI trait helps retain nitrogen for longer periods of time in the soil to facilitate its uptake by crops and reduce the loss of nitrogen as nitrous oxide, a major greenhouse gas emitted primarily from croplands.

Rajan and Sakiko Okumoto, Ph.D., AgriLife Research plant physiologist and associate professor in the Department of Soil and Crop Sciences, have screened sorghum genotypes from the sorghum breeding program led by Bill Rooney, Ph.D., AgriLife Research sorghum breeder, professor and Borlaug-Monsanto Chair for Plant Breeding and International Crop Improvement.

Those with the BNI trait have undergone three years of field testing to confirm the decrease in nitrogen loss as nitrate and nitrous oxide.

“This is a new research initiative at Texas A&M AgriLife Research, and we are at the forefront of targeting the development of climate-smart crops with this trait,” Rajan said. “Our field data shows a substantial reduction in greenhouse gas emissions. We believe we can develop climate-smart sorghums to enhance fertilizer-use efficiency and reduce nitrous oxide emission.”

This grant allowed Okumoto to identify specific combinations of genes responsible for the BNI trait.

“We were able to build a model to predict and cherry-pick the lines we believe will be good, thanks to the support from USDA-NIFA, Panther RISE Grant Program funded by Prairie View A&M and Texas A&M, the United Sorghum Checkoff Program and Texas Sorghum Producers Board,” Okumoto said. “Now we have a clear path to introduce and utilize that model in the breeding program to make it even better.”

The team believes they are just getting started, as they have only looked at a tiny fraction of what Rooney has in his breeding program.

“BNI is a heritable trait,” Rooney said. “There is substantial variability of this trait in our current germplasm pool, and we can improve the trait significantly.”

It will be important to ensure no yield penalties are suffered, Rajan said. They want to conduct extensive field trials in all major sorghum-growing regions to develop best management practices that will tell a farmer how much they can reduce their fertilizer application rate without suffering yield reductions.

Their current data indicate that nitrification inhibitor activity seems to selectively target the nitrifying microbial populations and has minimal impact on the overall soil microbiomes. Sanjay Antony-Babu, an assistant professor and soil microbiologist with AgriLife Research, is investigating the effect of BNI on various soil microorganisms. This research is vital to secure soil health, linked to microbial diversity are not negatively impacted by BNI.

Besides grain and forage sorghum, bioenergy sorghum is a targeted crop to include the BNI trait, Rooney said. Bioenergy sorghum is a relatively new concept pioneered by AgriLife Research in Rooney’s sorghum breeding lab.

Bioenergy sorghum is a specific type of sorghum that grows for a long season and does not produce grain which allows greater drought tolerance and higher yield of cellulosic biomass, he said.

As with grain and forage sorghum, the incorporation of the BNI trait should reduce the amount of nitrogen fertilizer required for production as well as increasing the utilization efficiency of the nitrogen that is applied, Rooney said.

The ultimate goal, Rajan said, is to develop a climate-smart sorghum, one that would not only reduce the expense of fertilizers but could count toward reducing the environmental footprint. A climate-smart crop has the potential for the producer to get credit for those practices as well as benefit the environment.

“Nitrogen is essential to producing food, but its use can also cause issues,” she said. “Developing climate-smart crop varieties is an excellent solution as it can prevent substantial nitrogen escape through water or as a greenhouse gas.”