Effects of nitrogen fertiliser use on green house gas emissions and land use change

Summary Reducing N fertiliser rates could be used to reduce the greenhouse gas (GHG) emissions associated with the production of crops. However, the lower yields from reduced N fertiliser rates (kg ha -1 ) are likely to cause an expansion of the cropped area to maintain grain production (t) and any land use change (LUC) resulting from this will produce carbon emissions. This paper describes a model for quantifying the effects of N fertiliser on direct GHG emissions per tonne of crop product and the indirect GHG emissions that may accrue from LUC using wheat grown in the UK as a case study. Direct GHG emissions per tonne of grain were minimised by using 33 kg N ha -1 . Indirect LUC increased this to 148 kg N ha -1 , assuming that temperate grassland was converted to crop land to maintain grain production at lower N rates. The N rate for minimising GHG emissions was very sensitive to the type of LUC and several other factors.