Scientists meeting in Australia this week are aiming to raise the profile of a tropical grass family, which they believe could drastically reduce the greenhouse gas emissions from agriculture. Worldwide, the sector accounts for a third of all greenhouse gas emissions.

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Studies being presented at the 22nd International Grasslands Congress offer new evidence that a potent chemical mechanism operating in the roots of certain tropical grass, which can be used for livestock feed, has enormous potential to reduce emissions.

The mechanism, known as "biological nitrification inhibition" or BNI, reduces the conversion of nitrogen applied to soil as fertiliser into nitrous oxide. Nitrous oxide is the most powerful and aggressive greenhouse gas, with a global warming potential 300 times that of carbon dioxide. It accounts for almost 40 percent of total agricultural emissions.

Researchers at agriculture institutes are now championing Brachiaria grasses as potential means to cut agriculture's emissions footprint. The pasture grasses originate from Southern Africa, but are now grown more widely elsewhere, including South America. They capture atmospheric carbon and fix nitrogen in the soil, which enables them to grow well with a reduced need for external inputs.

Michael Peters, who leads research on forages at the International Centre for Tropical Agriculture (CIAT), was optimistic about the potential of new approaches using newly developed hybrid Brachiaria grasses. He said, "BNI offers what could be agriculture's best bet for keeping global climate change within manageable limits."

G.V. Subbarao, of the Japan International Research Center for Agricultural Sciences (JIRCAS), where research on the grasses has been ongoing for 15 years, added, "This approach offers tremendous possibilities to reduce nitrous oxide emissions and the leaching of polluting nitrates into water supplies, while also raising crop yields through more efficient use of nitrogen fertiliser."

"The problem is that today's crop and livestock systems are very 'leaky,'" Subbarao continued. "About 70 percent of the 150 million tons of nitrogen fertiliser applied globally is lost through nitrate leaching and nitrous oxide emissions; the lost fertiliser has an annual estimated value of US$90 billion."

As a result of recent breakthroughs in their research, scientists working with CIAT have developed the means to exploit the BNI phenomenon on a larger scale than was previously possible. CIAT researchers have found ways to increase BNI through plant breeding in different species of Brachiaria grasses, and new techniques have allowed for the rapid development of new varieties.

Trials deliver astounding results

Centre scientists have also gathered positive results from field trials – including evidence that a maize crop grown after Brachiaria humidicola pastures gave good yields with only half the amount of nitrogen fertiliser normally used, because more nitrogen was retained in the soil. In this trial, the researchers determined that BNI had boosted nitrogen-use efficiency by a factor of 3.8. At the conference in Australia, scientists also showed that the grasses' nitrate fixing ability benefitted wheat crops; wheat grown pastures where Brachiaria had previously been grown yielded much higher while requiring much less fertiliser than control crops.

Farmers in Colombia and Nicaragua, working with the German government,  are engaged in productivity and quality testing in livestock farming. Previous grass hybrids have increased milk and meat production by several orders of magnitude, compared to native savannah grasses, and by at least 30 percent, compared to commercial grass cultivars. Based on evaluation of the new hybrids and with the aid of simulation models, researchers are studying where else the hybrids can be introduced and on how large a scale.

"Livestock production provides livelihoods for a billion people, but it also contributes about half of agriculture's greenhouse gas emissions," CIAT's Peters explained. "BNI is a rare triple-win technology that's good for rural livelihoods as well as the global environment and climate. It defies the widespread notion that livestock are necessarily in the minus column of any food security and environmental calculation."

Grassland pastures account for the largest proportion of agricultural land worldwide, covering 3.2 billion hectares out of a global total of 4.9 billion. In Brazil alone, 11 million hectares of grassland have been converted to maize and soybean production, and another 35-40 million could be shifted to crop production in the near future, according to CIAT. The Centre suggests that, instead of more monocropping, growers in developing countries in particular should integrate Brachiaria grasses into mixed crop-livestock systems, which would have economic as well as environmental benefits.