A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Carbon and Nutrient Stocks and Trace Gas Fluxes in Agroforestry Systems on DegradedPastureland in the Central Amazon.E.C.M. FERNANDES 1* , E. WANDELLI 2 , K.A. McCAFFERY and M.A.RONDON 11. Cornell University, 2. EMBRAPA-CPAA*Dept. of Crop & Soil Sciences, 624 Bradfield Hall, Ithaca, NY 14853, USAecf3@cornell.edu; +1 (607) 255-1712.Rehabilitation of degraded pastureland in the Brazilian Amazon could yield significantenvironmental benefits in terms of C sequestration, enhanced water and nutrientconservation, reduction in GHG fluxes and increased biodiversity. We describe thedevelopment and performance of four agroforestry systems as alternatives for degradedpastures. In 9 years, the agroforestry systems accumulated 32-82 t/ha of abovegroundbiomass, which is lower than the biomass on abandoned pastures (112 t/ha).Approximately 50% of all root biomass is concentrated in the top 20 cm of soil. Litterstocks in the agroforestry systems (2.2 - 3.3 t/ha) are significantly lower than inabandoned pasture vegetation (3.9 t/ha). Wet season litter biomass is about 50% of thedry season litter. Carbon stocks down to 1m, ranged from 140 to 150 Mg/ha of which 6%is charcoal. Loss of C in the form of dissolved organic C is about 200 kg/ha/yr. Degradedpastures are net sources of methane (10ugCh4/m2/h). The recolonization of such areas by2-yr-old secondary vegetation, appears to reverse the flux into a net small sink. Methanesinks in soils under agroforestry (15-20 ug CH4/m2-h) have been increased relative toabandoned pastures (5-10 ug CH4/m2/h), but are 50% of forest sinks.