GREENHOUSE GAS EMISSIONS FROM SUGARCANE SOILS AND NITROGEN FERTILISER MANAGEMENT

WE PRESENT the results of two investigations into greenhouse gas emissions from acid-sulfate (ASS) sugarcane soils, one recent and one current, and evaluate the measurement techniques employed. Both projects have employed micrometeorological methods and the current one also uses chambers to verify the micrometeorological measurements. Both measurement systems have been found to be reliable and mutually consistent for carbon dioxide (CO2) and nitrous oxide (N2O), but differences between them in the case of methane (CH4) need to be resolved. The aim of the current project is to obtain continuous, season-long, verified data sets for emissions of CO2, N2O and CH4 from sugarcane soils, both the ASS of northern NSW and the non-ASS more representative of the Queensland cane producing areas. Results to date indicate that emissions of CO2 from ASS are in the top of the range for agricultural soils, while emissions of N2O from N-fertilised soils appear to be much higher than expected from agricultural soils, amounting at times to > 0.4 kg N/ha/d. Results for CH4 are equivocal: chambers indicate small emissions; micrometeorological measurements suggest emissions are non-trivial. Both soil heterogeneity and instrument resolution may be involved. A bigger data base is needed.