New paper finds sugarcane plantation is a net source of CO2 to the atmosphere

A new paper published in Agricultural and Forest Meteorology finds a sugarcane plantation in Brazil acts as a net source of CO2 to the atmosphere. The paper adds to several other peer-reviewed papers finding various agricultural and ocean sites act as net sources of CO2 rather than sinks.

Fluxes of CO₂ above a sugarcane plantation in Brazil

• Osvaldo M.R. Cabral^a, , , , 
• Humberto R. Rocha^b, 
• John H. Gash^c, 
• Marcos A.V. Ligo^a, 
• Nilza Patrícia Ramos^a, 
• Ana Paula Packer^a, 
• Eunice Reis Batista^a

• ^a Embrapa Meio Ambiente, CEP 13820-000, Jaguariúna, SP, Brazil
• ^b Universidade de São Paulo, R. do Matão 1226, CEP 05508-090, São Paulo, SP, Brazil
• ^c Centre for Ecology and Hydrology, Wallingford OX10 8BB, United Kingdom

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Highlights

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Seasonal variability of CO₂ fluxes in a sugarcane perennial bioenergy crop.

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Net carbon balance was measured during two climatically contrasting years.

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The dependence of CO₂ exchange from light and saturation deficits.

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Water use efficiency during the main growth phases of a sugarcane bioenergy system.

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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 ± 44 g C m⁻²; the gross ecosystem productivity (GEP) was 3612 ± 46 g C m⁻² and the ecosystem respiration (R_E) was 1648 ± 14 g C m⁻². The NEE and GEP totals in the second cycle (third ratoon, 374 days long) decreased 51% and 25%, respectively and R_E 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 ± 130 g C m⁻²and 403 ± 84 g C m⁻² in each cycle respectively [positive values indicate a net source]. Thus the sugarcane agrosystem was approximately carbon neutral in the second ratoon. Yield in stalks fresh weight (SFW) attained the regional average (8.3 kg SFW m⁻²). Although it was a carbon source to the atmosphere, observed productivity (6.2 kg SFW m⁻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 (4.3 g C kg⁻¹ H₂O) decreased only 5% in the second cycle.

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