Can biofertilisers replace chemical fertilisers?

The University of Cambridge's Giles Oldroyd helped James Tytko with this question from listener Douglas...

James - A very pressing question, Douglas, given the news we are to reach the Paris Agreement’s 1.5 degree temperature target in just 7 years and the contribution of synthetic fertilisers to the degradation of our environment. One University of Cambridge study found that, along with manure, fertilisers emit the equivalent of 2.6 gigatonnes of carbon per year - that’s more than the shipping and aviation industry combined! With me to explain the role biofertilisers might play in bringing this down is Giles Oldroyd from the Department of Plant Sciences at the University of Cambridge.

Giles - Hi James. Not only would replacing chemical fertilisers with biofertilisers greatly reduce the greenhouse gas emissions and pollution derived from agriculture, it would also be cheaper for farmers to practice! Most fertilisers are nitrogenous - they contain nitrogen - and a lot of energy is required to generate them. Most of this energy is derived from natural gas, making fertilisers costly, especially now with the higher costs of gas. As well as extensive greenhouse gas emissions, the application of fertilisers causes a release of nutrients into the natural environment and depletes biodiversity.

James - Biofertilisers instead make use of the ability of fungi and bacteria to capture essential nutrients, especially nitrogen and phosphorus, from the surrounding soil and air. Some species of bacteria possess an enzyme capable of converting molecular dinitrogen in the air into ammonia, a reactive form of nitrogen that plants can use.

Giles - Some plants form associations with these nitrogen-fixing bacteria, as well as with some fungi that help the plant capture sources of nitrogen, phosphorus and water from the soil.  Biofertilisers make use of these microbial associations, either directly with the target crop plants, or with co-cultivated plants that can form the associations.

James - The stumbling block to completely replacing inorganic fertilisers with biofertilisers is the levels of the nutrients one can currently deliver to crops using biofertilisers. But raising the utility of biofertilisers is an area of very active research in both public and private sectors.

Giles - Field trials are currently ongoing at the University of Cambridge looking at plants that get hypercolonised by the beneficial fungi, and a number of companies around the world are developing nitrogen-fixing bacteria to act as biofertilisers for cereal crops.

James - So, Douglas. Yes indeed the use of biofertilisers is advantageous over chemical fertilsiers owing to their reduced burden on the environment. Some fungi and bacteria form associations with plants and give them the nitrogen they would otherwise be getting from chemicals which are carbon intensive to produce and apply. Biofertislisers aren’t currently as efficient as they could be, but there are promising developments in this highly active research field.