Nitrogen pollution is a serious global problem, and we are all part of it because the food we eat comes from farms which use nitrogen, whether as synthetic fertilizer or in organic forms. When farmers use N efficiently, they not only protect the environment, they also save money. But to do that, they need to invest in equipment and new methods - so who pays for that? This resource uses farm data to give pupils practice in data manipulation and to explain the science of nitrate leaching and ammonia volatilization, and to discuss the advantages and disadvantages of various approaches including regulation, nutrient trading and changing customer behaviour. Powerpoint, teachers notes and pupil sheet, available in English and Welsh versions.