Agriculture in the Neotropics and ecosystem changes to the N cycle

Background/Question/Methods The nitrogen cycling has been disrupted in the Neotropics mainly due to the same drivers that changed the nitrogen cycle in the temperate zones of the globe in the past. The first difference between the tropics and the temperate zones is that in the tropics human actions that lead to a disruption of the nitrogen cycle are happening all at the same time, with less time to adequate responses by society. On the other hand, in the temperate zones disruption was made first by deforestation, followed by untreated domestic sewage being dumped in water bodies due to intensive urbanization process that overlapped the massive use of N-fertilizer after the Second Word War. Another important difference between temperate and tropical zones of the world regarding nitrogen is that temperate ecosystems of the temperate zones are mostly nitrogen poor, while mostly of the tropical ecosystems are nitrogen rich. Therefore, pathways of response between these two zones of the globe could be completely different. The main objective of our presentation is to discuss the intensity that the nitrogen cycle has been disrupted in the tropics exploring how this disruption may affect important ecosystem services like food, feed, and energy production and water provision.

Results/Conclusions The use of N-fertilizer in the most areas of the Neotropics had an unprecedent increase in the last decades. Taking Latin America that most of its area is in the subtropical and tropical areas of the Neotropics as an example, in the beginning of the 60xs only 5 kg N ha-1 of N-fertilizer was used over an area of arable land equivalent to 7% of the world's arable lands. Sixty years later, the use of N-fertilizer increased to 45 kg N ha-1 and the arable land increased to 12% of the total world's arable lands. Therefore, the N-rich ecosystems of the Neotropics are receiving an increasing amount of N without a thorough evaluation of its consequences. At the same time, in these sixty years urbanization rate had one of the most intense growths in the world, increasing to approximately 90% in the 2000xs. Most of the cities in the Neotropics do not treat domestic sewage, as a consequence rivers and estuary receive enormous amount of N with a series of consequences to the water chemistry and biodiversity. Such consequences will be discussed in our presentation.