In the last two decades, the strong increase of pasturelands over former rainforest areas has raised concerns about the climate change that such change in land cover might cause. In recent years, though, expansion of soybean croplands has been increasingly important in the agricultural growth in Amazonia. In this paper we use the climate model CCM3 to investigate whether the climate change due to soybean expansion in Amazonia would be any different from the one due to pastureland expansion. The land component of the model has been updated with new findings from the Large‐Scale Biosphere Experiment in Amazonia (LBA), and a new soybean micrometeorological experiment in Amazonia. Results show that the decrease in precipitation after a soybean extension is significantly higher when compared to the change after a pastureland extension, a consequence of the very high albedo of the soybean.

Brazil is responsible for 27% of the world production of soybeans and 7% of maize. Mato Grosso and Para states in Brazil are among the largest producer. The viability to the cultivation of maize (Zea mays) and soybeans (Glycine max), for future climate scenarios (2070-2100, GHG) is evaluated based on crop modeling (DSSAT) forced by observational data and regional climate simulations (HadRM3). The results demonstrated that a substantial reduction in the yield in particular for maize may be expected for the end of the 21 st century. Distinct results are found for soybeans. By applying the A2 climate changes scenario, soybean yield rises by up top 60% assuming optimum soil treatment and no water stress. However, by analyzing the inter-annual variability of crop yields for both maize and soybean, could be demonstrated larger year-to-year fluctuations under greenhouse warming conditions as compared to current conditions, leading to very low productivity by the end of the 21 st century. Therefore, these Brazilian states do not appear to be economically suitable for a future cultivation of maize and soybeans. Improved adaptation measures and soil management may however partially alleviate the negative climate change effect.

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CONSUMO HÍDRICO DA SOJA NO NORDESTE PARAENSE*  PAULO JORGE DE OLIVEIRA PONTE DE SOUZA1; SAMUEL ORTEGA-FARIAS2; EDSON JOSE PAULINO DA ROCHA3; ADRIANO MARLISOM LEAO DE SOUSA4 E EVERALDO BARREIROS DE SOUZA5 1Meteorologista, Prof. Dr. Agrometeorologia, Instituto Socioambiental e dos Recursos Hídricos, Universidade Federal Rural da Amazônia, UFRA/ISARH, paulo.jorge@ufra.edu.br2Engenheiro agrônomo, Prof. PHD. Agroclimatologia, Centro de Investigacion y transferência em Riego y agroclimatologia, Universida de Talca, UTALCA/CITRA, sortega@utalca.cl3Meteorologista, Prof. Dr. Meteorologia, Instituto de Geociências, Universidade Federal do Pará, UFPA/IG, eprocha@ufpa.br4Meteorologista, Prof. Dr. Hidrologia, Instituto Socioambiental e dos Recursos Hídricos, Universidade Federal Rural da Amazônia, UFRA/ISARH, adriano.souza@ufra.edu.br5Meteorologista, Prof. Dr. Meteorologia, Instituto de Geociências, Universidade Federal do Pará, UFPA/IG, everaldo@ufpa.br*Extraído da tese de doutorado do primeiro autor  1 RESUMO Diversas pesquisas realizadas no Brasil têm mostrado que o rendimento das culturas é influenciado por fatores climáticos, dentre eles o estresse hídrico. O consumo hídrico da soja varia com o desenvolvimento vegetal e em função das condições ambientais, com impactos relevantes em seu rendimento quando esta demanda não é atendida. Sendo assim, o objetivo deste estudo foi avaliar o consumo hídrico da soja (Glycine Max (L.) Merryl), variedade Tracajá, durante o ciclo cultural de 2007 em uma área experimental dentro de uma fazenda de produção comercial de soja no nordeste Paraense. A evapotranspiração real da cultura foi estimada pelo balanço de energia através da técnica da razão de Bowen. Os resultados permitem inferir que: i) o consumo hídrico da soja acompanhou a tendência do aumento no índice de área foliar (IAF), com máxima evapotranspiração durante o período de enchimento de grãos, cujo valor médio foi de 4,1±0,4 mm.dia-1; ii) baixos valores do fator de desacoplamento durante a fase inicial da cultura indicaram uma importante contribuição da evaporação do solo e maior controle estomático do processo; iii) com o fechamento do dossel houve uma diminuição do controle estomático indicando um aumento da contribuição da transpiração e o desacoplamento do dossel com a atmosfera, sendo a evapotranspiração controlada diretamente pela energia disponível; iv) reduções no conteúdo de água do solo durante a fase reprodutiva sugeriram um importante controle estomático na evapotranspiração da soja; v) o consumo total de água pela soja desde a fase V1 até a colheita foi de 335 mm. Palavras-chave: Fronteira agrícola, Razão de Bowen, Evapotranspiração.  SOUZA, P.J.O.P.; ORTEGA-FARIAS, S.; ROCHA, E.J.P.; SOUSA, A.M.L.; SOUZA, E.B.SOYBEAN WATER REQUIREMENT IN NORTHEAST OF PARÁ STATE   2 ABSTRACT Several studies conducted in Brazil have shown that crop yield is affected by different climatic factors, including water stress. Water consumption of soybean varies with plant development and environmental conditions, with significant impacts on its yield when this demand is not met. Water consumption of soybean crop (Glycine Max (L.) Merryl) grown during the 2007 crop cycle in a soybean production areas in the Amazon was investigated. The soybean water consumption followed the trend of increase in LAI, with maximum evapotranspiration during grain filling period, whose mean value was 4.1±0.4 mm.day-1. Low values of the decoupling factor during the initial phase of the crop indicated a considerable contribution of soil evaporation and a higher stomatal control of the process. After the canopy closure there was a decrease in stomatal control indicating an increment in the transpiration contribution besides a canopy decoupling with the atmosphere, which indicated a direct control of evapotranspiration by the available energy. Slight reductions in soil water content during the reproductive phase suggested a certain importance of stomatal control in soybean evapotranspiration. The total water consumption of soybean from the V1 stage until harvest was 335 mm. Keywords: Agricultural Border in the Amazon, Bowen Ratio, Evapotranspiration.