H41H-02
The fate of nitrogen fertilizer added to soy-maize agriculture in the Amazon basin: Quantifying N2O flux and losses to groundwater

Thursday, 17 December 2015: 08:15
3011 (Moscone West)
Kathi Jo Jankowski1, Christopher Neill2, Eric A Davidson3, Marcia Macedo4, Ciniro Costa Jr.5, Gillian L Galford6, Michael Thomas Coe7, Christine O'Connell8, Paulo M Brando7,9, Paul Lefebvre4, Leonardo Maracahipes9, Darlisson Nunes9 and Richard McHorney2, (1)Marine Biological Laboratory, Woods Hole, MA, United States, (2)Marine Biological Laboratory, Ecosystems Center, Woods Hole, MA, United States, (3)University of Maryland Center for Environmental Science Appalachian Laboratory, Frostburg, MD, United States, (4)Woods Hole Research Center, Falmouth, MA, United States, (5)CENA Center for Nuclear Energy in Agriculture, Piracicaba, Brazil, (6)University of Vermont, Burlington, VT, United States, (7)The Woods Hole Research Center, Falmouth, MA, United States, (8)University of Minnesota Twin Cities, Minneapolis, MN, United States, (9)IPAM Amazon Environmental Research Institute, Brasilia, Brazil
Abstract:
Deforestation and agricultural intensification are rapidly changing the landscape of southeastern Amazonia. With international pressure to reduce deforestation, many Brazilian farms have opted to intensify agriculture to a system of soybean-maize double cropping, and it has expanded rapidly in the last 10 years. Maize agriculture requires additional nitrogen (N) fertilizers, whose downstream fate is currently unknown. Typical fertilizer application rates range from 30-120 kg N ha-1, and have the potential to introduce large amounts of N to ecosystems of the Amazon basin, which can alter greenhouse gas flux and nutrient transport to groundwater and streams.

Little data on the fate of added fertilizers are available in the tropics in general, especially in this critical region of agricultural expansion. Therefore, we established a field-scale experiment to evaluate the fate of N fertilizer on Tanguro Ranch in Mato Grosso, Brazil, a region of rapidly expanding soy-maize double cropping. We measured greenhouse gas fluxes (N2O, CO2, and CH4), soil N content, losses to groundwater, and corn productivity across five levels of fertilizer addition (0-200 kg N ha-1) throughout an entire growing season.

We found that N2O flux increased with fertilizer addition, but was only significantly higher at 200 kg N ha-1. Surface soil N content increased after fertilizer addition, but decreased within weeks, and was quickly observed in subsurface soil water. Modeling results that scale these findings to the state of Mato Grosso suggest that this land use transition could create a substantial new source of N2O and CO2 to the atmosphere and has the potential to leach N fertilizer into groundwater and downstream. It is important to maintain forest code policies that minimize these impacts.

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