The objective of this study was to investigate the application of the 15N natural abundance technique to quantify BNF inputs to different varieties of field-grown sugarcane. The experiment was planted on a low-fertility sandy soil and no N fertilizer was added. Cane yields of seven Brazilian commercial varieties at the first harvest after 18 months were similar to the mean national yields. Nitrogen accumulation of most varieties exceeded 100 kg N ha−1 yr−1 even after two ratoons. The 15N abundance values of reference weed plants at the first harvest were significantly higher than leaf sample of the cane indicating inputs of BNF between 80 and 170 kg N ha−1 during the plant crop (18 months). The hypothesis that the lower 15N abundance of the cane varieties was due to the deeper rooting habit of the cane enabling it to access mineral N of significantly lower 15N abundance than present in the rooting zone of weed reference species was discarded, as weed reference species grown in soil samples taken at seven depth intervals to 75 cm showed higher 15N abundance than samples taken from the surface 10 cm. Weeds taken from the plots of the ratoon crops did not differ significantly in 15N abundance from the sugarcane varieties which suggested insignificant contributions of BNF at this time.

The aim of this paper is to analyse the effects of climate change on irrigation adoption in Brazil. Temperature and precipitation projections for the 2010-2099 periods were employed under a number of different climate scenarios according the 4th Assessment Report of Intergovernmental Panel on Climate Change (IPCC). The results show that irrigation adoption will be affected by climate change. Given current conditions, irrigation has generally been adopted in Brazil to cope with reduced precipitation and temperature variations. The estimated irrigation probabilities in the future scenarios were quite different across Brazilian regions. The main explanation for this pattern is the distinct climatic conditions and production structures. Considering future climate change, over the next 30 years (2010 to 2039), the irrigation probability is expected to increase in all Brazilian regions. However, this trend is reversed in the long run.

O objetivo do presente estudo foi analisar a distribuição espacial dos componentes da evapotranspiração de referência modificada (ETr) no Brasil e, posteriormente, a variabilidade temporal por meio da técnica da análise harmônica. Para isso, foi feita inicialmente uma análise de variância, fase e amplitude para o tempo presente (1980-2000) e, em seguida, feita uma projeção com o tempo futuro (2080-2100), com base no cenário A2 do Painel Intergovernamental para as Mudanças Climáticas. A equação utilizada foi a de Penman-Monteith, padronizada pela Food and Agriculture and Organization of the United Nations (FAO) 1998. As simulações foram conduzidas com o modelo regional de clima (MM5), acoplado a um modelo de vegetação potencial (MVP). Os termos aerodinâmico e radiativo apresentaram um ciclo anual que é dominante na região amazônica e Sul do Brasil, enquanto na região Sudeste o ciclo semestral tem maior destaque. As maiores variações na amplitude da ETr foram identificadas no semiárido nordestino e no extremo sul do Brasil. As mudanças na ETr, devido ao aquecimento global, foram máximas na região central do Brasil e Amazônica. Ainda foi observado que, sob condições de aquecimento global, as variações do termo aerodinâmico tornam-se mais importantes do que as variações do termo radiativo para a ETr total.

O artigo apresenta os efeitos de mudanças climáticas sobre a economia da Bahia. Os principais resultados indicaram uma variação negativa do PIB real da Bahia entre -0,028% e -0,114%, em um cenário, e entre -0,029% e -0,075% no outro. Estes dados, associados ao fato de que a Bahia possui produtividade agrícola de algumas culturas inferior à média nacional, sugerem que políticas públicas e privadas podem ser adotadas para mitigar os efeitos de mudanças climáticas e aumentar o desempenho, em termos de produção agrícola, relativo aos outros estados do Brasil (incentivo ao cultivo alternativo de algumas lavouras e medidas de estímulo para adaptação às mudanças climáticas). Os resultados foram obtidos a partir do desenvolvimento de um modelo de equilíbrio geral computável (EGC) com especificação detalhada do uso da terra para a Bahia. Tal especificação foi incorporada no modelo de forma a considerar 13 distintos usos da terra. Para analisar os efeitos econômicos de mudanças climáticas, foi utiliza-da uma metodologia que integrou o EGC a um modelo econométrico. As simulações tiveram como referência informações de um período-base e de projeções e cenários climáticos do IPCC.

The Brazilian Northeast (NE) is strongly affected by El Niño–Southern Oscillation (ENSO). During La Niña events, the precipitation over the NE is generally above average. However, during the last La Niña event in 2011–2012, the NE went through its worst drought in the last 30 years. In this study, observations and numerical simulations are used to determine what made the 2011–2012 event different from other events. We find that eastern Pacific (canonical) La Niña events cause a cooling of the tropical North Atlantic and warming of the tropical South Atlantic that lead to a southward migration of the Intertropical Convergence Zone, which in turn brings rain to the NE. On the other hand, La Niña events with the cooling concentrated in the central Pacific cause the opposite meridional sea surface temperature (SST) gradient in the tropical Atlantic, leading to droughts over the NE. The 2011–2012 event was of the latter type. This study also shows that it is possible to predict the sign of the NE rainfall anomaly during ENSO events using a simple SST index.

It has recently been found that the frequency distribution of remotely sensed tree cover in the tropics has three distinct modes, which seem to correspond to forest, savanna, and treeless states. This pattern has been suggested to imply that these states represent alternative attractors, and that the response of these systems to climate change would be characterized by critical transitions and hysteresis. Here, we show how this inference is contingent upon mechanisms at play. We present a simple dynamical model that can generate three alternative tree cover states (forest, savanna, and a treeless state), based on known mechanisms, and use this model to simulate patterns of tree cover under different scenarios. We use these synthetic data to show that the hysteresis inferred from remotely sensed tree cover patterns will be inflated by spatial heterogeneity of environmental conditions. On the other hand, we show that the hysteresis inferred from satellite data may actually underestimate real hysteresis in response to climate change if there exists a positive feedback between regional tree cover and precipitation. Our results also indicate that such positive feedback between vegetation and climate should cause direct shifts between forest and a treeless state (rather than through an intermediate savanna state) to become more likely. Finally, we show how directionality of historical change in conditions may bias the observed relationship between tree cover and environmental conditions.

Changes in agricultural land use have important implications for environmental services. Previous studies of agricultural land-use futures have been published indicating large uncertainty due to different model assumptions and methodologies. In this article we present a first comprehensive comparison of global agro-economic models that have harmonized drivers of population, GDP, and biophysical yields. The comparison allows us to ask two research questions: (1) How much cropland will be used under different socioeconomic and climate change scenarios? (2) How can differences in model results be explained? The comparison includes four partial and six general equilibrium models that differ in how they model land supply and amount of potentially available land. We analyze results of two different socioeconomic scenarios and three climate scenarios (one with constant climate). Most models (7 out of 10) project an increase of cropland of 10–25% by 2050 compared to 2005 (under constant climate), but one model projects a decrease. Pasture land expands in some models, which increase the treat on natural vegetation further. Across all models most of the cropland expansion takes place in South America and sub-Saharan Africa. In general, the strongest differences in model results are related to differences in the costs of land expansion, the endogenous productivity responses, and the assumptions about potential cropland.

In this paper we analyze the indirect land use change (ILUC) effects of ethanol production expansion in Brazil through the use of an inter-regional, bottom-up, dynamic general equilibrium model calibrated with the 2005 Brazilian I-O table. A new methodology to deal with ILUC effects is developed, using a transition matrix of land uses calibrated with Agricultural Censuses data. Agriculture and land use are modeled separately in each of 15 Brazilian regions with different agricultural mix. This regional detail captures a good deal of the differences in soil, climate and history that cause particular land to be used for particular purposes.

Brazilian land area data distinguish three broad types of agricultural land use, Crop, Pasture, and Plantation Forestry. Between one year and the next the model allows land to move between those categories, or for unused land to convert to one of these three, driven initially by the transition matrix, changing land supply for agriculture between years. The transition matrix shows Markov probabilities that a particular hectare of land used in one year for some use would be in another use next period. These probabilities are modified endogenously in the model according to the average unit rentals of each land type in each region.

We ask whether biofuel expansion is consistent with new laws, limiting forest clearing in Brazil. A simulation with ethanol expansion scenario is performed for year 2020, in which land supply is allowed to increase only in states located on the agricultural frontier. Results suggest that each new hectare of sugar cane requires only 0.14 ha of new land, with another 0.47 ha converted from pasture use. Hence policies limiting deforestation are unlikely to prevent greater ethanol production. Finally, regional differences in sugarcane productivity are found to be important elements in ILUC effects of sugar cane expansion.

Climate change is expected to alter a multitude of factors important to agricultural systems, including pests, diseases, weeds, extreme climate events, water respources, soil degradation, and socio-economic pressures. Changes to carbon dioxide concentrations ([CO2]), temperature and water (CTW) will be the primary drivers of climate change in crop growth and agricultural systems. Therefore, establishing the CTW-chnage sensitivity of crop yields is an urgent research need and warrants diverse methods of investigation.