Agriculture contributes to greenhouse gas emissions: all agricultural activities require inputs of energy and will therefore result in at least CO2 emissions, and additionally because of the central importance of N in crop production, ammonia and NOX emissions are also prevalent. In the case of irrigated rice production, methane, which is at least 20-fold more effective than CO2 as a GHG, can be a significant polluting emission (Yan et al., 2003). With respect to emissions from agriculture, the next 50 years will be the most critical, as anticipated improvements in global agricultural production to supply the demand of the world population are expected to be a major driver in climate change (Tilman et al., 2001). While any crop improvement directed at yield increases would theoretically alleviate the detrimental impacts of crop production if demand was not increasing, there is likely to be more activity, in a wider area and utilizing higher inputs to supply worldwide production demand. Alleviating environmental impact is more likely to arise as a consequence of specifically targeting reduced inputs, for example in relation to fertilizers or pesticides. Reduced inputs will aid reductions in emissions, principally those GHGs associated with energy production and manufacturing. In addition reducing N fertilizer requirements and therefore inputs will have a substantial effect on ammonia and NOX emissions. Improving efficiency of use of other fertilizers will also reduce environmental impacts such as coastal algal blooms which also result in gaseous emissions (see Ortiz-Monasterio et al., Chapter 9, this volume).
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