Field application of organic and inorganic fertilizers

Nitrogen (N) is the nutrient recovered in largest quantities from soil by agricultural crops, and the availability of N to crops has a dominant impact on crop yields and nutritional quality, and hence the ability of farms to produce food for humanity. Management of the different N inputs to agricultural soils will influence the subsequent N cycling, N utilization by crops and losses of N in different forms to the environment. Until now, the focus has largely been on controlling individual N loss pathways, for example, nitrate leaching (European Union Nitrates Directive), ammonia (Gothenburg Protocol, European Union National Emissions Ceilings Directive23 and Habitats Directive) and nitrous oxide (Kyoto Protocol to the United Nations Framework Convention on Climate Change), with guidance given accordingly (for example, UNECE Ammonia Guidance Document, Bittman and others, 2014). It is critical when trying to develop a more joined-up approach to N guidance to have a good understanding of how management practices and targeted abatement/mitigation measures have an impact on the whole N cycle rather than just on specific pathways. This requires an understanding of how human activity, including farming, is able to affect all nutrient cycles, and especially N, which is highly dependent on microbiological activities and hence particularly sensitive to soil carbon, moisture and temperature. This chapter discusses integrated approaches to reducing N losses to air and water from N inputs to agricultural land, highlighting the major inputs and loss pathways, while describing the most important measures and prioritizing recommendations