Nitrogen

Nitrogen - the important constituent of NPK contributes to Global Warming. Nitrogen contributes to global warming in 2 main ways

1.Energy to produce artificial fertilisers

2. Emissions from breakdown products

The Stern Review 2006 calcualted that nearly 40% of all GHGs from farming came from nitrogen use.

Production

Energy to produce artifical fertil;isers.

The N2 molecule that makes 4/5 of our air has a very strong bond. This needs energy to break down in order to make other compounds like ammonia NH3

The industrial process which does this is called Haber-Bosch. It is like a pressure cooker process - ie raised temperatures and pressures.

Early after Russian invasion of Ukraine, when energy prices shot up, the only N-fertiliser factory in UK threatened to close. Government finance kept it going for a short while.

Emissions

Emissions from breakdown products contribute GHG

After nitrogen has been applied as fertiliser or fixed by bacteria, it becomes incorporated into organic molecules, which provide essential plant nutrients. Some stays bound in these molecules until it is 'mineralised' and so released into the soil as ammonia.

Nitrogen breakdown products - nitrous oxides - are released from the soil. Nitrous oxides are major GHGs and each molecule 300X more potent than CO2

Pollution

Many rivers worldwide are polluted with nitrate runoff which encourages alga which remove oxygen from the water causing it to die off - eutrophication. There are many schemes involving farmers and river authorities to reduce this runoff to rivers. Dairy farms are particulary

Nitrogen fixing

In soils there are 'Nitrogen-fixing' bacteria. They perform the breakdown of N2 in normal temperatures and pressures. Free living N-fixing bacteria include Azotobacter which has been around for about 400 million years.

There are also N-fixing bacteria found in the nodules of legume roots. They only appeared about 100 million years ago, and seem to have developed in relation to mycorrhiza as they both have similar metabolic processes. It has seemed impossible to transfer this N-fixing mechanism to grass crops likek wheat and rice, which has become the agriculturl scientist 'holy grail'

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