The Impact of Crop Management and Rotation Sequences On Greenhouse Gas Emissions From Temperate and Tropical Soils.

The synergistic determination of carbon dioxide, methane and nitrous oxide fluxes from soils is essential for comprehensive greenhouse accounting and provides valuable insight into the interactions between the carbon and nitrogen cycles. We detail a high temporal resolution, fully automated greenhouse gas monitoring network with manually sampled satellite deployments in Australia and an analogous system in Michigan, for assessing the impact of crop management and rotation sequences on greenhouse gas emissions from a wide variety of crop, pasture and mixed farming systems. In Australia, nitrous oxide emissions ranged from < 1 kg/ha/annum from semi-arid soils to > 1 kg/annum/day in soils under intensive dairy production (receiving urine based nitrogen inputs) and wheat following a long-term pasture phase. Nitrification inhibitors have a positive impact on the reduction of nitrous oxide emissions. Methane emissions have also been also detected in rainfed sugar cane systems.  In Michigan, we have examined the relationship between the rate of nitrogen fertilizer application on nitrous oxide emissions to develop a nitrogen reduction protocol suitable for carbon offsets. The availability of a labile form of organic carbon is the key determinant of nitrous oxide emissions when soils are saturated. The automated systems overcome many of the environmental constraints associated with the manual sampling of greenhouse gas emissions from soils as multiple measurements are easily taken over any 24 hour period regardless of the soil or climatic condition (e.g. waterlogged, storm events).