Agricultural soils have long been thought of as sinks for atmospheric gases. However, coastal acid sulfate soils (ASS) under sugarcane cropping, have recently been identified by the authors as a source of sulfur dioxide (SO₂). Sugarcane cropping is a major landuse along the Australian east coast, occupying over 400,000 ha., a large proportion of which is underlain by ASS.

By utilising ultraviolet fluorescence spectrometry and flux-gradient micrometeorological techniques, we have subsequently measured emissions of SO₂ and hydrogen sulfide (H₂S) from ASS cultivated for sugarcane production in Australia. This work suggests that the emissions of SO₂ are linked to the formation of H₂S, most likely from the bacterial reduction of sulfate within the soil profile. It is proposed that the H₂S is subsequently oxidised at the soil surface to SO₂ by ultraviolet light.

Increased H₂S fluxes at the ground surface during the night, and decreased fluxes during the day have been measured along with an inverse relationship with SO₂ fluxes. This diurnal process will most likely reflect the availability of organic matter as well as the more obvious influence of light and temperature cycles. The interactions between SO₂ and H₂S and the parameters influencing their emission have been further explored using laboratory based gas chromatography.

Drained ASS, such as those under sugarcane cropping, are a potentially significant unaccounted source of H₂S in the biogenic atmospheric sulfur cycle. Such areas were most likely mapped as agricultural lands rather than drained backswamps, and therefore assigned a flux value of zero. Our measurements show that H₂S emissions from drained ASS are comparable to undrained freshwater and saltwater wetlands, which are major contributors to the global biogenic H₂S budget.