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Regional gains and losses of nitrogen in the Amazon basin

  • E. Salati
  • R. Sylvester-Bradley
  • R. L. Victoria
Part of the Developments in Plant and Soil Sciences book series (DPSS, volume 6)

Abstract

In order to better understand the relative importance of different ecosystems and nitrogen cycling processes within the Amazon basin to the nitrogen economy of this region, we constructed a generalized nitrogen budget for the region based on data for hydrologic losses of nitrogen and nitrogen fixation in Amazon forests. Data included information available for nitrogen in water entering and leaving both the entire basin and watersheds on oxisol and ultisol soils near Manaus, Brazil, in addition to biological nitrogen fixation in forests on ultisol, oxisol and entisol (‘varzea’) soils in Central Amazonia.

Available data indicate that 4–6 kg N ha-1 yr-1 are lost via the River Amazonas, and that a similar amount enters in rainfall. Root-associated biological nitrogen fixation contributes ca. 2kg N ha-1 yr-1 to forests on oxisols, 20kg N ha-1 yr-1 to forests on utisols, and 200kg N ha-1 yr-1 to forests on fertile varzea soils. There is 5–10 fold more NH4 +-N than NO3-N in rain and stream water entering and leaving the waterbasin near Manaus.

Calculations based on these data plus certain assumptions yield the following regional nitrogen balance estimate: inputs through bulk deposition of 36 × 108 kg N yr-1 and through biological nitrogen fixation of 120 × 108 kg N yr-1, and outputs via the River Amazonas of 36 × 108 kg N yr-1 and via denitrification and volatilization (by difference) of 120 × 108 kg N yr-1.

Key words

Amazonas Hydrologic losses N-cycling N2-fixation Oxisol Streamflow Regional budget Ultisoldf 

Ganancias y pérdidas regionales de nitrógeno en la cuenca Amazónica

Resumen

Con el fin de comprender la importancia relativa de los ecosistemas y los procesos del ciclo de nitrógeno dentro de la cuenca Amazónica, hemos establecido un balance generalizado para este elemento basado en los datos de pérdidas de nitrógeno por las aguas y la fijación biológica en los bosques Amazónicos. Se incluye en el modelo la información disponible para las aguas que entran y salen de la cuenca entera asi como para una cuenca experimental sobre oxisoles y ultisoles cerca de Manaus, Brasil. También se incluyen datos de fijación biológica de nitrógeno en suelos diferentes de la Amazonia Central.

Entre 4–6kg N ha-1 año-1 salen por el rio Amazonas y cantidades semejantes entran al sistema por precipitación. La fijación biológica de nitrógeno en las raices contribuye con ca. 2kg N ha-1 año-1 en bosques sobre oxisoles, 20kg N ha-1 año-1 en bosques sobre ultisoles y unos 200kg N ha-1 año-1 en bosques sobre entisoles mas fértiles en la ‘varzea’. La relación NH4-N vs NO3-N está alrededor de 5–10 tanto para las aguas de lluvia como para las de los rios cerca de Manaus.

Para la cuenca del Amazonas se obtuvo, basándose en los datos arriba mencionados y en algunas premises, el siguiente balance regional. Entradas por precipitación, 36 × 108 kg N año-1; fijación biológica de nitrógeno, 120 × 108 kg año-1. Las salidas por el rio Amazonas, 36 × 108 kg N año-1 y por desnitrificación y volatilización (por diferencia), 120 × 108 kg N año-1.

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Copyright information

© Martinus Nijhoff/Dr W. Junk Publishers, The Hague 1982

Authors and Affiliations

  • E. Salati
    • 1
  • R. Sylvester-Bradley
    • 2
  • R. L. Victoria
    • 1
  1. 1.Centro de Energia Nuclear na Agricultura (CENA)PiracicabaBrazil
  2. 2.Centro Internacional de Agricultura Tropical (CIAT)CaliColombia

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