Biogeochemical consequences of land-use transitions
along Brazil's agricultural frontier
Gillian Galford, Jack Mustard, and Jerry Melillo
The southwestern Brazilian Amazon is undergoing rapid conversion of cattle pastures and natural vegetation to mechanized agriculture, including soybean, maize, dry-land rice and millet. From 1990 to 2000, soybean cover doubled while production has nearly quadrupled due to farm mechanization [1]. A major frontier of mechanized agriculture is in the states of Mato Grosso and Rondnia (Figure 1), home of some of the largest contiguous row crop plantations in the world. In Mato Grosso the area planted in soybean has increased on average 19.4% annually since 1999. By 2004 over 5 million hectares, or about 6% of Mato Grosso, was soybean plantations [1].
In Mato Grosso and Rondnia, there are three major natural vegetation types: forests, cerrado (woody savanna) and cerrado (open savanna). Land-use transitions from forest involve a two-step pathway: forest to pasture, and then pasture to row crops. There are two pathways to row crops in cerrado and cerrado: natural vegetation to pasture to row crops; and natural vegetation directly to row crops. Row crops are subject to a variety of management regimes - types and sequences of crops; types, timing and amounts of fertilizer and other chemicals; and tillage versus no-tillage.
The biogeochemical consequences of land-cover transitions and row crop management in the Brazilian Amazon, including changes in greenhouse gas fluxes, have been widely investigated (e.g., 2-4) but little attention has been paid to mechanized agriculture expansion. New data sets (Moderate Resolution Imaging Spectroradiometer, MODIS) when combined with process-based models will advance our understanding of the biogeochemical consequences of rapid land cover conversion. The primary objective of this research is to understand how the massive transition from natural vegetation and pasture to mechanized agriculture affects the biogeochemistry of the southwestern Brazilian Amazon.
Sources
- CONAB (Companhia Nacional de Abastecimento). 2004. www.conab.gov.br
- Luizo, F. et al. 1989. Nitrous oxide fluxes following tropical land clearing. Global Biogeochem. Cycles, 3:281-285.
- Melillo, J.M. et al. 2001. Nitrous oxide emissions from forests and pastures of various ages in the Brazilian Amazon.
J. Geophys. Res. 106(D24):34,179-34,188. - DeFries, R.S. et al. 2002. Carbon emissions from tropical deforestation and regrowth based on satellite observations for the 1980s and 1990s. PNAS 99(22): 14256-14261.
Figure 1. Brazilian Amazon states of Mato Grosso and Rondnia highlighted in a map of Brazil. The study area encompasses the area in both states north of Cuiab.
Figure 2. EVI Time series for 2000-2006. Line "*" shows forest phenology. Agricultural phenology (2000-2006) is shown with a double crop in 2004 indicated by (a). At a nearby location, the conversion of natural vegetation (b) to agriculture (c) can be observed. Data is offset by 0.7 EVI for clarity.
Images of the study landscape (click each image to see a larger version)
Native cerradão vegetation next to a corn field in southern Rondônia.
Tilled soybean field, Comodoro, Mato Grosso, awaiting the next wet season planting.
Gillian and Ado doing field work in the pastures of Nova Vida, Rondônia.
Cows looking on expectantly.
A pasture in Nova Vida Ranch, Rondônia with rainforest in the background.
Fertilizer delivery for the next growing season. Each bag contains 1,000 kilograms of fertilizer.
Updated
05/22/2008
envstudies@brown.edu