3 October 2017
By David Dent, Chief Technical Officer and a Founder Director of Azotic Technologies Ltd.
Nitrogen is crucial to agriculture and no plant can grow without it. To manufacture nitrogen fertilizer, 500 million tonnes of ammonia are produced each year, accounting for 1% of the world’s energy usage and 3-5% of natural gas usage.
However, crops use only an estimated 30-50% of the nitrogen fertilizer applied to the soil. The remainder is lost, either to the atmosphere as nitrous oxide gas or into our waterways as nitrate run-off. Agricultural nitrogen fertilizer use accounts for 66% of UK nitrous oxide emissions, contributing to climate change, while nitrate run-off contaminates drinking water, with 5% of the European population exposed to unsafe levels.
We face a seemingly intractable problem: we require ever more nitrogen fertilizer in order to feed the world’s burgeoning population, but we need to reduce its use in order to lower greenhouse gas emissions and nitrate pollution.
A possible answer
Biological nitrogen fixation (BNF) in crops provides a possible answer. This is the process by which a specialised group of bacteria can capture nitrogen gas from the atmosphere and convert it to a form that plants can use.
Research on BNF in crops began with work on Rhizobium bacteria, which form nodules in the roots of leguminous plants, in which they provide the plants with a source of nitrogen.
We are now starting to realise the potential of BNF in non-leguminous crops, with other candidate nitrogen-fixing bacteria. Primary among these is Gluconacetobacter diazotrophicus. This strain of nitrogen-fixing bacteria is an endophyte, meaning that it lives inside plant tissues, and in this case, inside the plant cells. First discovered in Brazilian sugarcane in 1988, G. diazotrophicus has since been isolated from around the world in other high sucrose content crops, including sweet potato, sweet sorghum, pineapple and mango.
A significant breakthrough
Professor Ted Cocking at the Nottingham University made the first significant breakthrough in 2006. He and his team identified isolates and conditions in which G. diazotrophicus could colonise a range of crop plants, living within their cells.
At that time, the idea that nitrogen-fixing bacteria could colonise plant cells outside of root nodules was somewhat controversial. Subsequently, however, symbiotic relationships with other bacteria have been demonstrated in plants such as peach palm, cactus, banana, spruce and pine trees.
Research with isolates of G. diazotrophicus, cultured and delivered as seed treatments, demonstrates its ability to:
- Colonise a wide range of non-leguminous crop species through natural routes of entry
- Intracellularly colonise living plant cells in order to form a symbiotic relationship
- Move throughout the roots and the above-ground biomass.
- Fix nitrogen under a range of different fertilizer regimes and environmental conditions
- Promote additional plant growth or yield benefits.
Field trials have demonstrated that G. diazotrophicus – applied as a seed coating – can increase yields in wheat, maize and rice by up to one tonne per hectare at any level of nitrogen fertilizer.
Through biological nitrogen fixation, meeting food security needs while mitigating against climate change emissions now comes into prospect!