Nitrates in Belgian soils: What if plants had a bigger role to play?
Recently, the European Commission has confronted Belgium with the problem of nitrate pollution of its waters. Among the solutions already considered, Prof. Cécile Thonar and Prof. Hervé Vanderschuren (Université Libre de Bruxelles and Gembloux Agro-Bio Tech - ULiège) have come up with a new approach: the use of "BNI" plants with a nitrification inhibition potential (BNI for Biological Nitrification Inhibition).
The problem has been known for a long time: the unreasonable use of fertilizers in agriculture to enrich the soil in nitrogen causes an overabundance of nitrate (NO3-) that the plant cannot absorb in its entirety.
This excess is then washed away by rainwater or irrigation water into the groundwater and waterways, which is called "leaching". This phenomenon has direct repercussions on biodiversity by promoting the proliferation of algae in waterways and on drinking water, which requires expensive treatment when its nitrate level is too high.
Among all the approaches considered, Prof. Cécile Thonar and Hervé Vanderschuren, are focusing on a new angle to deal with the problem: the plant itself.
"There are indeed different complementary expertises on the Gembloux Agro BioTech campus that allow us to have an integrated approach at the soil level. Until now, we had not really looked at the possibility of reinforcing the "plant" aspect in their contributions to the complex equation of nitrate pollution by focusing on their capacity to influence the microbiological activities of the soil. Is it possible, for example, to select and use in the rotation plants that better regulate nitrification following the application of fertilizers on agricultural plots? Prof. Hervé Vanderschuren
Indeed, in order to grow, a plant needs nitrogen which it captures in the soil in the form of ammonium (NH4+) or nitrate (NO3-) (with often a preference for the NO3- form). The conversion of ammonium to nitrate, also called nitrification, is carried out by soil microorganisms.
Some plants are able to control this nitrification process by releasing organic compounds that they secrete into the soil from their roots. These compounds are called BNI (Biological Nitrification Inhibitors).
Schematic view of nitrification and denitrification processes in the soil
Through " Catch-BNI ", a European project coordinated by the laboratory Plant Genetics and Rhizosphere Processes and gathering several research institutions (ULB in Belgium, IPK in Germany, John Innes Centre in the United Kingdom, University of the Basque Country in Spain and TERRA at Gembloux Agro-Bio Tech), Prof. Cécile Thonar and Hervé Vanderschuren are studying and selecting the plants that show the best results in terms of BNI. To do this, they compare the properties of different species and varieties of the same species (mustard, phacelia, sorghum, oats, plantain, wheat...) using various tools to quantify their ability to inhibit nitrification and thus better control the appearance of nitrate in the soil.
These plants could thus limit or slow down nitrification in a natural way in order to reduce nitrate losses by leaching as well as theemission of greenhouse gases such as nitrous oxide (N2O) which is also generated during nitrification-denitrification processes. This approach could also appeal to farmers because of the possibility of reducing the amount of fertilizer they need to apply to their fields.
"With the increase in fertilizer prices and the recurrent environmental problems posed by nitrate pollution, there is a real potential to develop alternative approaches to reduce nitrate losses and thus increase the efficiency of fertilizer use by crops
In order to evaluate the BNI potential of cultivated plants as well as those used in interculture, the laboratory Plant Genetics and Rhizosphere Processes has developed a hydroponic screening platform to isolate and test BNI compounds produced and exuded by roots. This platform has been used to identify and characterize "BNI" wheat varieties in the framework of the GAIN project financed by the Walloon Region. This work carried out by the researchers of the laboratory has highlighted BNI activities in wheat and is the subject of a publication in the prestigious journal New Phytologist (Jauregui et al., 2023).
The hydroponic platform and other tools are also being used to extend and refine the analyses to intercrop plants, i.e., plants planted between two main crops, to provide new insights for better control of the soil nitrogen cycle at times of the year that are prone to nitrate leaching problems.
For more information:
https://www.suscrop.eu/projects-second-call/catch-bni
https://www.catch-bni.uliege.be/
Iván Jáuregui, Izargi Vega-Mas, Pierre Delaplace, Hervé Vanderschuren, Cécile Thonar. An optimized hydroponic pipeline for large-scale identification of wheat genotypes with resilient biological nitrification inhibition activity. (2023) New Phytologist, https://doi.org/10.1111/nph.18807
