Fluxes of CO2 above a sugarcane plantation in Brazil

Abstract

Fluxes of CO2 were measured above a sugarcane plantation using the eddy-covariance method covering two growth cycles, representing the second and third re-growth (ratoons) harvested with stubble burning. The total net ecosystem exchange (NEE) in the first cycle (second ratoon, 393 days long) was −1964±44gCm−2; the gross ecosystem productivity (GEP) was 3612±46gCm−2 and the ecosystem respiration (RE) was 1648±14gCm−2. The NEE and GEP totals in the second cycle (third ratoon, 374 days long) decreased 51% and 25%, respectively and RE increased 7%. Accounting for the carbon emitted during biomass burning and the removal of stalks at harvest, net ecosystem carbon balance (NECB) totals were 102±130gCm−2 and 403±84gCm−2 in each cycle respectively. Thus the sugarcane agrosystem was approximately carbon neutral in the second ratoon. Yield in stalks fresh weight (SFW) attained the regional average (8.3kgSFWm−2). Although it was a carbon source to the atmosphere, observed productivity (6.2kgSFWm−2) of the third ratoon was 19% lower than the regional average due to the lower water availability observed during the initial 120 days of re-growth. However, the overall water use efficiency (WUE) achieved in the first cycle (4.3gCkg−1H2O) decreased only 5% in the second cycle.