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MBL/Brown Graduate Student Tracks Advance of Amazon Agriculture

The southwestern Brazilian Amazon is one of the world’s largest agricultural frontiers. Native vegetation and pastures are rapidly being converted to heavily mechanized row-crop agriculture, including soybean and corn. Researchers from MBL’s Ecosystems Center and Brown University are studying how regional land cover and land use change affect carbon (CO2) and nitrogen (N2O) emissions to the atmosphere.

MBL-Brown graduate student Gillian Galford is lead author on an article that has been published in Remote Sensing of Environment that shows the extent to which forests and savanna ecosystems are being cleared, not for cow pastures as they were in the past, but for row-crop agriculture. In their study area of 40,000 km2, more than 3,200 km2 (8%) were converted to row-crops within the period of 2000-2005. In addition, farmers are using techniques to increase production per acre. For example, instead of a single crop of soybeans, they are now planting double crops of soybeans and corn within a single season. In the study area, the researchers observed an increase of 2,000 km2 of this type of agricultural intensification.

Dr. Carlos Eduardo Cerri (ESALQ, Universidade de São Paulo) and students going to make trace gas emission measurements on tilled soybean field, formerly natural cerrado (savanna), in Mato Grosso state, Brazil. Photo credit: Gillian Galford.

The purpose of the MBL-Brown study, conducted by Ms. Galford, Jerry Melillo of MBL, John Mustard and Aline Gendrin, both of Brown, and Carlos C. Cerri and Carlos E. P. Cerri, both of Universidade de São Paulo, was to track the transformation of forested land to agricultural cropland through space and time. The authors developed remote sensing methodologies utilizing over 300 satellite observations from the MODIS sensor and the methods are now being extrapolated to the larger region. The next step is to assess the land use impacts on carbon and nitrogen cycling.

“Distinguishing crop types, such as soybean and corn, is important as different crops have different implications for carbon and nitrogen cycling,” according to Ms. Galford. “Soybean plants fix nitrogen, but most of the fixed nitrogen leaves the system at harvest. Without proper management, over time, the loss of carbon and nitrogen decreases the soil fertility and may have other implications for land-use sustainability and management. Secondary crops, such as corn, may require large inputs of nitrogen fertilizers that increase nitrous oxide emissions. Addition of nitrogen fertilizers also impact local water quality.”

Galford, G.L., J. F. Mustard, J. M. Melillo, A. Gendrin, C. C. Cerri and C. E. P. Cerri. 2008. Wavelet analysis of MODIS time series to detect expansion and intensification of row-crop agriculture in Brazil. Remote Sensing of Environment 112(2):576-587.