Nitrogen (N)

Nitrogen is actually not a mineral, but a gaseous element which makes up 78% of the Earth's atmosphere. It is arguably the most important nutrient in plant growth and without it there would be no plants. It is found in the soil in three forms; organic N compounds in organic matter, ammonium ions (NH4) and nitrate ions (NO3).

This year the famed Haber-Bosch process will manufacture 500 million tonnes of ammonia for the fertiliser industry by direct hydrogenation of nitrogen with hydrogen gas over a catalyst. However, this process needs temperatures of around 450°C and pressures of 300 bar, consuming vast amounts of energy. The energy comes from fossil fuels; usually natural gas. This year's usage will be about 182 billion (182,000,000,000) cubic feet of gas.

Until the Haber-Bosch process was invented, all plant nitrogen was fixed in the soil by bacteria on the root systems of leguminous plants. This system is still the only source of nitrogen for the organic farmer, but it is argued that the world could only support a human population of 3 billion without Haber-Bosch. Short of shooting the surplus population, to reduce energy use we have to find ways to utilise N fertilisers more efficiently (the average N use efficiency is only 30%). First we must bind nitrogen to the soil to stop it from volatizing into the atmosphere (35%), which is wasteful and polluting. Also from slipping through the rootzone into our watercourses (35%) which is wasteful, polluting and carcinogenic.

Fortunately, the German chemical industry is developing a new process using a ruthenium rare earth metal catalyst that can do the job at atmospheric pressure and at a temperature of 50°C. We wish them well.