a. Manufacturing and transport of fertiliser are estimated at 6.7 tonnes CO2e for each tonne of Nitrogen fertiliser. Thus as 850,000 tonnes used in UK, this = 5.7mt CO2e. Out of a total UK GHGs of about 180 mtonnes, this = about 3%.

b Add to this the nitrous emissions following fertilser application. In the UK, NOx are 6 per cent. of UK greenhouse gas emissions (parliamentary answer). Agriculture contributes 2/3 of this - ie 4%.

A Life Cycle Analysis (DEFRA funded) into the environmental burdens and resource use in the production of agricultural and horticultural commodities shows that Nitrous oxide (N2O) is the single largest contributor to global warming potential (GWP) for all commodities except tomatoes. Summary of findings

So N fertilisers are responsible for 3 + 4 = 7% of all UK GHG emissions - more than for all aircraft (a mere 10mt - see total UK GHGs )

Livestock accounts for about 65% of human made nitrous oxides according to LEAD.

Nitrous oxide is a major contributor to climate change (4-6% in UK) - and about 300X more potent than carbon dioxide.

2. Uses masses of oil.

The manufacture of Nitrogen fertiliser is the single main cause of energy use in non-organic farming, accounting for 37% of the total. More from Soil Association.