LINDELL BEACH, B.C. — The power of grass roots has taken on a promising dimension.
Research has provided evidence that a chemical mechanism in the roots of tropical grasses such as brachiaria can reduce the conversion of nitrogen fertilizer to nitrous oxide, which is one of the most potent of greenhouse gases.
The mechanism is biological nitrification inhibition (BNI), and brachiaria is on track to become a modern day super grass.
“The biological nitrification inhibitors released by brachiaria roots markedly reduce the process of nitrification in soil (conversion of ammonium to nitrate) mediated by nitrifying micro-organisms,” said Michael Peters, research leader on forages at the International Center for Tropical Agriculture (CIAT) in Colombia.
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“The decrease in formation of nitrate reduces the risk for nitrate pollution (surface and ground water systems) and nitrous oxide (N2O) emission to the atmosphere. Thus, nitrogen remains available for the plant in the form of ammonium, and nitrogen use efficiency is improved by 30 percent to 50 percent. (This) means you need less nitrogen application for the same yield as we were able to show with (corn) after pasture in a forage-crop rotation. This has potential economic benefits alongside reducing nitrate leaching into the ground water and nitrous oxide into the atmosphere.”
There are 100 species of brachiaria grasses, also known as signal grass. It is native to tropical and subtropical regions, especially in sub-Saharan Africa.
Seeds may have been unintentionally transported to Central and South America centuries ago in bedding on slave ships, where it rapidly established and spread.
The plant can grow a metre high, tolerate dry conditions and intense light and grow in infertile and acidic soils. It is the most important forage grass in the tropics, and Brazil has become the leading user and producer of brachiaria.
Soil microbiologist Rosemary Sylvester-Bradley of CIAT first noticed BNI’s beneficial mechanism 15 years ago, and a research article was published in 1988.
Since then, CIAT scientists have worked with the Japan International Research Center for Agricultural Sciences (JIRCAS) to continue the re-search. Their latest research was presented this year at the International Grasslands Congress.
Nitrogen fertilizer’s impact is significant.
Peters said about 150 million tonnes of nitrogen fertilizer are applied annually to agricultural systems, of which only 30 percent is recovered and moved into the food system. The lost fertilizer amounts to an annual economic loss of $90 billion US.
Livestock production provides a livelihood for a billion people but contributes half of agriculture’s greenhouse gas emissions.
Brazil has already converted 27 million acres of grassland to intensive corn and soybean production, and another 100 million acres could be converted to crops.
However, the CIAT scientists said grassland pastures are the biggest resource for agricultural land. Out of a global total of 12 billion acres, grasslands account for eight billion acres. Rather than practice monoculture production, they encourage the use of brachiaria grasses in mixed crop-livestock systems.
“Over the last 15 years, the BNI process has been characterized, evaluation methods have been developed and a major biological nitrification inhibitor (brachialactone) responsible for BNI has been identified and patented by JIRCAS and its partners,” said Peters.
“What is new is to apply the concept in different agricultural systems where forage grasses such as brachiaria are integrated into crop-livestock production to reduce nitrogen fertilizer applications for the benefit of agriculture and the environment.”
A corn crop that followed brachiaria grasses in a mixed crop-livestock system produced yields that needed only half the amount of nitrogen fertilizer because more nitrogen was retained in the soil.
As well, there were less nitrate leaching and nitrous oxide emissions. CIAT scientists estimated that the BNI boosted nitrogen efficiency by a factor of 3.8.
The BNI mechanism also exists in temperate grass species and research has already begun on grass hybrids.
“AgResearch in New Zealand is conducting research on this topic using different temperate grasses compared with one brachiaria cultivar,” Peters said.
“But for the tropics, different germplasm accessions of brachiaria humidicola showed greater potential for BNI. It is possible to develop hybrids of temperate grasses by applying the concept of BNI.”
Farmers are using hybrids of brachiaria humidicola in Colombia and Nicaragua, where the grass is monitored for productivity and quality. Previous hybrids have resulted in better milk and meat production than native savannah-type grasses, and research continues to evaluate the benefits.
Peters said that Brachiaria grasses are grown throughout the tropics and subtropics of the Americas, Australia, Asia, and Africa.
“B. humidicola is particularly adapted to low fertility soils and waterlogged conditions,” he said.
“Brachiaria is grown on more than 250 million acres in Latin American and Caribbean (LAC) countries alone and is likely the crop with the widest extension in LAC.”
Not only do the grass roots apply their BNI mechanism for efficient nitrogen use, but additional research has shown that deep rooted brachiaria grasses are enormous carbon sinks. The plants capture large amounts of atmospheric carbon on a scale comparable to tropical forests, which further mitigates global warming.
The BNI research is part of a larger initiative called Livestock Plus, which falls under the umbrella network of a global partnership known as the Consultative Group on International Agricultural Research. The key goal is to deliver major benefits for the poor and the environment through innovative research on forage grasses and crops.
“The topic of BNI received wide attention at the grassland congress, not only from the scientific community but local and international media,” said Peters.
