Iron Oxides in the Characterizing of Soil CO2 Emission.

Soil CO₂ emission, also known as soil respiration, is the second largest source of emissions of CO₂ to the atmosphere, following only to burning of fossil fuels. Soil CO₂  emission is related to soil attributes including porosity, density and moisture, which related to gas transfer, O₂ uptake and CO₂ release, as well as to mineralogical components (particularly iron oxides, which are closely associated to the aggregation and protection of organic matter in soil). The primary purpose of this work was to assess the use of the mineralogical attributes hematite, goethite, as estimated by diffuse reflectance spectroscopy, and iron oxides extracted by dithionite-citrate-bicarbonate (Fe_dcb) for estimating soil CO₂ emission and other soil properties in a sugarcane area under green harvest in south-eastern Brazil. The study was conducted in a regular 150 m X 150 m grid containing 56 sampling points to assess the previous soil attributes.  It was observed a positive correlation between iron oxides and CO₂ emissions. Geostatistical data revealed the presence of spatial dependence in CO₂ emission, hematite, goethite and Fe_dcb. These results confirm the usefulness of diffuse reflectance spectroscopy as an auxiliary tool for soil CO₂ emission characterization, with a potential of mapping this property in large agricultural areas.