Ammonia mitigation from urea fertilized crops: the case of Spain

The current pattern of food and energy consumption (and wastes management) as well as the combination of a growing world population and the limitations for expanding agricultural lands has leaded to an intensification of agricultural systems.

The development and use of synthetic fertilisers has been one of the official responses to this need.

Nitrogen (N) losses from agriculture can be up to 70% of the fertiliser N applied, depending on management practices, climate and soil conditions.

Besides the decreased effectiveness of the applied fertiliser, ammonia (NH3) losses are responsible for environmental problems such as acidification and N enrichment of natural ecosystems, as well as public health problems related to particulate matter (aerosols) formation.

In response to this situation, the United Nations and the European Union have promoted the development of legal initiatives to control and reduce the NH3 emitted from N-fertilised land.

Mitigation strategies must always be implemented taking into account local climatic and soil conditions and all synergies between NH3 mitigation and other components of the N cycle.

Among the proposed mitigation strategies (e.g. from UNECE), the use of those focused on enhancing the contact between the ammonium (NH4+) and the soil colloid have been encouraged the most. The aim of the work presented in the seminar is to synthesise and assess the NH3 abatement techniques and strategies producing a cost-effective mitigation and decreasing potential trade-offs in the form of other N losses (e.g. N2O and NO3-).

This study regionally focused in Spain and, since urea is the most used synthetic N fertilized, we considered the N applied to crops in this N form as the starting point in the assessment of different mitigation alternatives.

These ranged from UNECE proposed measures (e.g. incorporation of urea and use of urease inhibitors) to the substitution of urea by organic fertilizers (i.e. slurries, manures, wastewater sludge differently managed, redistributed and properly applied) as well as structural changes (e.g. decrease of animal protein consumption and thus in N fertilized land).

Although this study focuses on a specific region, the methodology used here could be extended to other countries and regions aiming to get an overall picture of a problem of increasing concern: NH3 losses from agrosystems.