Soil Carbon Stocks and Dynamics in Acre: Contrasts with the Remaining Brazilian Amazon
Antonio
Willian Flores de
Melo, Centro de Energia Nuclear na Agricultura - USP/Parque Zoobotânico - UFAC, awfmelo@cena.usp.br
(Presenting)
Plínio
Barbosa de
Camargo, Centro de Energia Nuclear na Agricultura - USP, pcamargo@cena.usp.br
Cleber
Ibraim
Salimon, Centro de Energia Nuclear na Agricultura - USP, clebsal@cena.usp.br
Eric
A.
Davidson, The Woods Hole Research Center, edavidson@whrc.org
Susan
E.
Trumbore, University of California, setrumbo@uci.edu
Judson
Ferreira
Valentim, Centro de Pesquisa Agroflorestal do Acre - Embrapa, judson@cpafac.embrapa.br
Soils are an important carbon reservoir, and Amazonian soils store about 66 Pg C. Acre soils, which are under the influence of the on-going uplift of the Andes, are distinct from the most dominant soils in Brazilian Amazonia. Soils in Acre are mostly Inceptisols, Alfisols, and Ultisols, and are frequently eutrophic, pedogenetically young, and comparatively unweathered. Little is known about the impacts of land use change on soil organic matter under these circumstances. The present study focused on: (1) the effect of land-use change on carbon stocks and delta 13C, and (2) estimating carbon stocks of the most common soils occurring in the state. We determined the C content, delta 13C and bulk soil density in pastures of 5, 12-15, and 20 years and in 2 intact forests in depths from 0 to 100 cm, on Ultisols (well drained) and Alfisols (poorly drained). A carbon stock map was created using a soil map (scale 1:1.000.000) and also data from previous soil surveys. Soils in Acre store about 1 Pg C to 1m depth. Eutrophic soils contain smaller C stocks than dystrophic soils within the same soil order. The rate of decomposition of carbon in Alfisols is lower than in Ultisols, but the mean residence time of organic matter is longer. The Ultisols tend to lose more carbon with land-use change. Based on soil carbon data, the productivity of Brachiaria brizantha cv. Marandu pastures is probably lower on Alfisols, indicating that, in addition to soil fertility, other characteristics such as soil drainage affect pasture productivity and carbon dynamics.