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Scoping the potential to reduce GHG emissions associated with N fertiliser applied to arable crops - AC0221

Description
A significant proportion of greenhouse gas (GHG) emissions associated with the production of arable crops result from the use of nitrogen (N) fertiliser. For example N fertiliser has been estimated to contribute 75 to 79% of the GHG emissions associated with wheat and oilseed rape production respectively (Berry et al., 2008; Mahmuti et al., 2009). Greenhouse gas emissions associated with N fertiliser are in the form of nitrous oxide (N2O) and carbon dioxide (CO2) released during the manufacture and application processes. Nitrous oxide accounts for approximately 60% of the total agricultural GHG output, and 35% of the total is directly attributable to mineral N application through denitrification, volatilisation and leaching.

Greenhouse gas emissions associated with N fertiliser use may be reduced by simply reducing N rates, but it is recognised that this would reduce crop yields and transfer GHG emissions to wherever the yield shortfall is made up, and may even increase GHG emissions as a result of greater indirect land use change (ILUC) (Kindred et al., 2008). There are three broad methods by which changes to crop management may reduce the GHG emissions associated with N fertiliser without reducing yield including; i) reducing the N rate required to achieve a given yield, ii) increasing yield for a given N rate and iii) reducing the N2O emissions for a given rate of N. Methods i and iii will reduce the GHGs included in the UK IPCC inventory of GHG emissions, whilst method ii will reduce GHGs per tonne of produce and reduce GHG release through ILUC.

Previous research has identified optimising N timing and avoiding excess N as possible methods for reducing GHGs within a short time-scale. The rationale behind optimising N timing is that a) N2O emissions may be minimised by improving the synchrony between N application and crop N uptake, b) it may be possible to increase yield for a given amount of N by optimising N timings to maximise yield and c) it may be possible to minimise N2O emissions by avoiding application when environmental factors favour the release of N2O. The issue of avoiding excess N may be better defined as improving the prediction of N requirement because this also encompasses under-fertilisation which, as described above, may also lead to greater indirect GHG emissions. Methods for predicting N requirement exist (e.g. RB209 and PLANET), but there is significant scope for improvement both in terms of increasing use of existing prediction methods and by improving the methods themselves. Improving the precision of fertiliser applications offers a route to reducing GHG emissions in the short-term. However, it is clear that there is much greater potential for reducing GHGs through breeding N efficient varieties and through developing end-use technology that minimises the requirement for grain protein.

The aim of this project is to estimate the extent to which GHG emissions associated with N fertiliser use on arable crops in England could be reduced through optimal N timing, improving the prediction of N requirement and the development of longer-term technologies. Published literature and existing datasets will be used to quantify the optimum N timings for minimising GHG emissions, together with the maximum level of precision that fertiliser requirements may be predicted using current technology. Existing survey information (e.g. British Survey of Fertiliser Practice), a phone survey with farmers and focus groups with farmers and agronomists will then be used to gauge the extent to which farmers may practically be able to alter N timing towards the optimum and improve the prediction of fertiliser requirement. Barriers that may constrain improvement will be identified and potentially influencing factors, such as region, farm type and soil type, will be analysed. Information from current Defra LINK projects will be analysed to assess the potential and identify barriers for reducing N requirement and GHG emissions by breeding N efficient crop varieties. An expert group approach will be used to assess the potential to develop technologies for making bread from wheat with low protein and to estimate the reduction in fertiliser N that this would result in. Finally the project will estimate realistic changes to N use and GHG emissions that could be achieved with timescales.
Objective
7b. Objectives

The aim of this project is to estimate the extent to which GHG emissions associated with N fertiliser use on arable crops in England could be reduced through optimal N timing, improving the prediction of N requirement and the development of longer-term technologies. This will be achieved through the following objectives;

1) Estimate the potential to increase yield and reduce GHG emissions through altering N timing and assess whether this is influenced by factors such as region.
2) Estimate the level of imprecision in N fertiliser use and the effect on GHG emissions.
3) Evaluate the scope for altering N timing towards the optimum for minimising GHGs, identify barriers for change and assess whether these are influenced by factors such as region.
4) Evaluate the scope for minimising imprecision of fertiliser use and identify barriers for change.
5) Assess the potential for minimising fertiliser N requirement through the development of N efficient varieties and low N bread technology.
6) Estimate realistic changes to N use and GHG emissions that could be achieved with timescales.
Project Documents
• Final Report : Scoping the potential to reduce GHG emissions associated with N fertiliser applied to arable crops   (942k)
• Final Report - Annex : AC0221 Annex 1   (147k)
• Final Report - Annex : AC0221 Annex 2   (913k)
• Final Report - Annex : AC0221 Annex 3   (135k)
• Final Report - Annex : AC0221 Annex 4   (300k)
• Final Report - Annex : AC0221 Annex 5   (454k)
• Final Report - Annex : AC0221 Annex 6   (218k)
• Final Report - Annex : AC0221 Annex 7   (155k)
• Final Report - Annex : AC0221 References   (129k)
Time-Scale and Cost
From: 2009

To: 2010

Cost: £80,000
Contractor / Funded Organisations
ADAS UK Ltd.
Keywords
Agriculture and Climate Change              
Fertiliser Application              
Mitigation              
Nitrous oxide              
Sustainable Farming and Food              
Sustainable Farming and Food Science              
Fields of Study
Agriculture and Climate Change