In western France, farmers are experimenting with an unconventional fertilizer: a powder made from algae grown on sewage.
The results are encouraging: when mixed with mineral fertilizers, this biological product can reduce their use by 25% without reducing yields.
“We have grown single-celled algae on the dairy effluent of a food processing plant,” explains Orhan Grignon, Agriculture and Environment Advisor.
“The algae feed on the organic matter in the wastewater, turning it into plant biomass. We then dewater this biomass and spread it on the fields as fertilizer because it is rich in nitrogen,” he said.
In tests conducted on wheat plots, the algae powder was compared with mineral fertilizers and other organic products. The verdict: algae on its own cannot match mineral fertilizers for yield, but when combined with them, it gives the same results while reducing the amount of additives used by a quarter.
