Organic Matter of Tropical Soil with Coffee Growthin CO2 Enriched Atmosphere

The increase of atmospheric CO 2 should result in higher carbon fixation by plants of the C3 photosynthetic cycle, such as coffee.However, not much is known about the relationship between atmospheric CO 2 increase, higher carbon fixation through photosynthesis and the potential carbon sequestration in soil.Based on the hypothesis that there will be greater stabilization of carbon in soil due to increase of atmospheric CO 2 concentration, the study was carried a field coffee grown area with FACE (Free-Air Carbon dioxide Enrichment) system.The CO 2 enrichment treatment maintained the concentration of this gas 200 μmol mol -1 above the ambient value.The stocks of carbon and nitrogen in soil and some attributes related to the humification of organic matter were evaluated 43 months after the beginning of the experiment.In addition, the decomposition of residues of coffee plants (leaves) and the emission of N 2 O were also evaluated.The stocks of carbon and nitrogen in soil of at 0-5 cm layer were in average 18% higher (2.6 Mg ha -1 carbon and 0.2 Mg ha -1 nitrogen) in CO 2 enrichment treatment.As the decomposition of vegetal remains was not affected by atmospheric CO 2 enrichment, the increase of carbon and nitrogen in soil was due to the greater contribution of vegetal material, which resulted in a less humic organic matter.In the equilibrium between carbon soil stabilization and N 2 O emission, the enrichment of atmospheric CO 2 in the coffee crop resulted in negative feedback for global warming due to the increased sequestration potential of carbon by soil.