Brazilian agriculture covers about one-third of the land area and is expected to expand further. We assessed the compliance of present Brazilian agriculture with environmental legislation and identified challenges for agricultural development connected to this legislation. We found (i) minor illegal land use in protected areas under public administration, (ii) a large deficit in legal reserves and protected riparian zones on private farmland, and (iii) large areas of unprotected natural vegetation in regions experiencing agriculture expansion. Achieving full compliance with the environmental laws as they presently stand would require drastic changes in agricultural land use, where large agricultural areas are taken out of production and converted back to natural vegetation. The outcome of a full compliance with environmental legislation might not be satisfactory due to leakage, where pristine unprotected areas become converted to compensate for lost production as current agricultural areas are reconverted to protected natural vegetation. Realizing the desired protection of biodiversity and natural vegetation, while expanding agriculture to meet food and biofuel demand, may require a new approach to environmental protection. New legal and regulatory instruments and the establishment of alternative development models should be considered.
The intensive land use invariably has several negative effects on the environment and crop production if conservative practices are not adopted. Reduction in soil organic matter (SOM) quantity means gas emission (mainly CO 2 , CH 4 , N 2 O) to the atmosphere and increased global warming. Soil sustainability is also affected, since remaining SOM quality changes. Alterations can be verified, for example, by soil desegregation and changes in structure. The consequences are erosion, reduction in nutrient availability for the plants and lower water retention capacity. These and other factors reflect negatively on crop productivity and sustainability of the soil-plant-atmosphere system. Conversely, adoption of "best management practices", such as conservation tillage, can partly reverse the process -they are aimed at increasing the input of organic matter to the soil and/or decreasing the rates at which soil organic matter decomposes. Key words: Brazil, climate change, greenhouse effect, soil organic matter, management practices
AGRICULTURA TROPICAL E AQUECIMENTO GLOBAL: IMPACTOS E OPÇÕES DE MITIGAÇÃORESUMO: O uso intensivo da terra invariavelmente causa efeitos negativos ao ambiente e produção agrícola se práticas conservativas não forem adotadas. Redução na quantidade de matéria orgânica do solo significa emissão de gases (principalmente CO 2 , CH 4 , N 2 O) para a atmosfera e aumento do aquecimento global. A sustentabilidade do solo é também afetada, uma vez que a qualidade da matéria orgânica remanescente muda. Alterações podem ser verificadas, por exemplo, pela desagregação do solo e mudança na sua estrutura. As consequências são erosão, redução na disponibilidade de nutrientes para as plantas e baixa capacidade de retenção de água no solo. Estes e outros fatores refletem negativamente na produtivade das culturas e sustentabilidade do sistema solo-planta-atmosfera. Ao contrário, a adoção de boas práticas de manejo, tal como o sistema plantio direto, pode parcialmente reverter o processo, uma vez que objetiva o aumento das entradas de material orgânico no solo e/ou diminuição das taxas de decomposição da matéria orgânica do solo. Palavras-chave: Brasil, mudanças climáticas, efeito estufa, matéria orgânica do solo, boas práticas de manejo
A strategy to measure bacterial functional redundancy was developed and tested with soils collected along a soil reclamation gradient by determining the richness and diversity of bacterial groups capable of in situ growth on selected carbon substrates. Soil cores were collected from four sites along a transect from the Jamari tin mine site in the Jamari National Forest, Rondonia, RO, Brazil: denuded mine spoil, soil from below the canopy of invading pioneer trees, revegetated soil under new growth on the forest edge, and the forest floor of an adjacent preserved forest. Bacterial population responses were analyzed by amending these soil samples with individual carbon substrates in the presence of bromodeoxyuridine (BrdU). BrdU-labeled DNA was then subjected to a 16S-23S rRNA intergenic analysis to depict the actively growing bacteria from each site. The number and diversity of bacterial groups responding to four carbon substrates (L-serine, L-threonine, sodium citrate, and ␣-lactose hydrate) increased along the reclamation-vegetation gradient such that the preserved forest soil samples contained the highest functional redundancy for each substrate. These data suggest that bacterial functional redundancy increases in relation to the regrowth of plant communities and may therefore represent an important aspect of the restoration of soil biological functionality to reclaimed mine spoils. They also suggest that bacterial functional redundancy may be a useful indicator of soil quality and ecosystem functioning.
Does agricultural intensification reduce the area used for agricultural production in Brazil? Census and other data for time periods 1975-1996 and 1996-2006 were processed and analyzed using Geographic Information System and statistical tools to investigate whether and if so, how, changes in yield and stocking rate coincide with changes in cropland and pasture area. Complementary medium-resolution data on total farmland area changes were used in a spatially explicit assessment of the land-use transitions that occurred in Brazil during 1960-2006. The analyses show that in agriculturally consolidated areas (mainly southern and southeastern Brazil), land-use intensification (both on cropland and pastures) coincided with either contraction of both cropland and pasture areas, or cropland expansion at the expense of pastures, both cases resulting in farmland stability or contraction. In contrast, in agricultural frontier areas (i.e., the deforestation zones in central and northern Brazil), land-use intensification coincided with expansion of agricultural lands. These observations provide support for the thesis that (i) technological improvements create incentives for expansion in agricultural frontier areas; and (ii) farmers are likely to reduce their managed acreage only if land becomes a scarce resource. The spatially explicit examination of land-use transitions since 1960 reveals an expansion and gradual movement of the agricultural frontier toward the interior (center-western Cerrado) of Brazil. It also indicates a possible initiation of a reversed trend in line with the forest transition theory, i.e., agricultural contraction and recurring forests in marginally suitable areas in southeastern Brazil, mainly within the Atlantic Forest biome. The significant reduction in deforestation that has taken place in recent years, despite rising food commodity prices, indicates that policies put in place to curb conversion of native vegetation to agriculture land might be effective. This can improve the prospects for protecting native vegetation by investing in agricultural intensification.
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