The greenhouse gases concentration in the atmosphere have significantly increased since the beginning of the Industrial Revolution. The most important greenhouse gases are CO2, CH4 and N2O, with CH4 and N2O presenting global warming potentials 25 and 298 times higher than CO2, respectively. Most of the N2O emissions take place in soils and are related with agricultural activities. So, this review article aimed at presenting the mechanisms of N2O formation and emission in agricultural soils, as well as gathering and discussing information on how soil management practices may be used to reduce such emissions. The N2O formation in the soil occurs mainly through nitrification and denitrification processes, which are influenced by soil moisture, temperature, oxygen concentration, amount of available organic carbon and nitrogen and soil C/N ratio. Among these factors, those related to soil could be easily altered by management practices. Therefore, understanding the processes of N2O formation in soils and the factors influencing these emissions is fundamental to develop efficient strategies to reduce N2O emissions in agricultural soils.

Among the main greenhouse gases (CO 2 , CH 4 and N 2 O), N 2 O has the highest global warming potential. N 2 O emission is mainly connected to agricultural activities, increasing as nitrogen concentrations increase in the soil with nitrogen fertilizer application. We evaluated N 2 O emissions due to application of increasing doses of ammonium nitrate and urea in two sugarcane fields in the mid-southern region of Brazil: Piracicaba (São Paulo state) and Goianésia (Goiás state). In Piracicaba, N 2 O emissions exponentially increased with increasing N doses and were similar for urea and ammonium nitrate up to a dose of 107.9 kg ha −1 of N. From there on, emissions exponentially increased for ammonium nitrate, whereas for urea they stabilized. In Goianésia, N 2 O emissions were lower, although the behavior was similar to that at the Piracicaba site. Ammonium nitrate emissions increased linearly with N dose and urea emissions were adjusted to a quadratic equation with a maximum amount of 113.9 kg N ha −1 . This first effort to measure fertilizer induced emissions in Brazilian sugarcane production not only helps to elucidate the behavior of N 2 O emissions promoted by different N sources frequently used in Brazilian sugarcane fields but also can be useful for future Brazilian ethanol carbon footprint studies.

Anthropogenic forest disturbance and land use change (LUC) in the Amazon region is the main source of greenhouse gas emissions to the atmosphere in Brazil, due to the carbon (C) and nitrogen (N) emitted from vegetation clearance. Land use conversion associated with management practices plays a key role in the distribution and origin of C in different soil organic matter (SOM) fractions. Here, we show how changing land use systems have influenced soil C and N stocks, SOM physical fractions, and the origin of SOM in the Santarém region of the eastern Brazilian Amazon. Soil C and N stocks were calculated for the surface layer of 0-30 cm. Anthropogenic disturbances to the standing forest, such as selective logging and wildfires, led to significant declines in soil C and N stocks. However, in the long-term, the conversion of the Amazon forest to pasture did not have a noticeable effect on soil C and N stocks, presumably because of additional inputs from pasture grasses. However, the conversion to cropland did lead to reductions in soil C and N content. According to the physical fractionation of SOM, LUC altered SOM quality, but silt and clay remained the combined fraction that contributed the most to soil C storage. Our results emphasize the importance of implementing more sustainable forest management systems, whilst also calling further attention to the need for fire monitoring systems, helping to ensure the resilience of C and N stocks and sequestration in forest soils; thereby contributing towards urgently needed ongoing efforts to mitigate climate change.

RESUMOA cana-de-açúcar é a principal cultura utilizada na produção de etanol biocombustível no Brasil e sua colheita pode ser feita com ou sem queima das folhas, aumentando ou diminuindo a emissão de gases do efeito estufa e a deposição de C no solo. Por meio deste trabalho, avaliou-se o efeito de sistemas de colheita de cana-de-açúcar (com e sem queima da palha, com um, três e seis anos após a última reforma do canavial) sobre os teores e estoques de C no solo, a qualidade física da matéria orgânica e a imobilização de C na biomassa microbiana do solo. As áreas de colheita sem queima apresentaram maior teor de C na camada superficial e maiores estoques de C, independentemente do tempo após a última reforma. Diferenças na qualidade física da matéria orgânica ocorreram principalmente na fração com tamanho entre 53 e 75 µ µ µ µ µm, na qual a proporção de C foi maior nas áreas sem queima. Na camada de 0-10 cm, o sistema sem queima apresentou maior teor de C microbiano. A colheita sem queima da palha é eficiente em acumular C em formas que possuem alto tempo de residência no solo.Termos de indexação: aquecimento global, cana crua, fracionamento físico, manejo do solo, matéria orgânica do solo.

Soil organic matter (SOM), which influences chemical, physical and biological soil attributes, is the main form of C found in the soil which can also be used as a soil sustainability index. The aim of this study was to use the quantity and quality of SOM as an indicator to determine the sustainability of different land uses (native vegetation, secondary vegetation, fruit orchards, horticultural areas, degraded pasture, improved pasture, and fields with annual crops) in the eastern Amazon. Improved pasture had higher soil C stock than the other land uses and was similar to the native vegetation, and also presented the highest quantity of C in a stable form in the soil (fraction < 53 µm). According to the C management index, improved pasture is the most similar in use to native vegetation. Changes in land use reduced the soil microbial C content, although the more conservationist systems (fruit orchards, secondary vegetation, and improved pasture) had contents similar to those of the native vegetation. The highest soil microbial quotients were found in fruit orchards and horticultural areas. Well-managed pastures were effective in accumulating C as stable forms in the soil, which demonstrates the sustainability of this land use in the region studied.

No abstract

ResumoBiocombustíveis contribuem para reduzir as emissões de gases de efeito estufa (GEE). No Brasil, o principal biocombustível é o etanol de cana-de-açúcar. Além dos colmos, as folhas de cana-de-açúcar também podem ser usadas para produzir etanol. O objetivo deste trabalho foi avaliar as emissões de GEE (CO 2 , CH 4 e N 2 O) induzidas pela presença de palha sobre o solo. Três experimentos foram conduzidos em Latossolos, em Piracicaba: imediatamente após a colheita, aos seis e aos 12 meses após a colheita. Foram avaliados os efeitos de três doses de palha (0%, 50% e 100% da quantidade disponível na superfície) sobre as emissões. Imediatamente após a colheita, as emissões de CO 2 e CH 4 aumentaram com o aumento da quantidade de palha. Aos seis meses após a colheita houve consumo de CH 4 à medida que a quantidade de palha aumentou. Doze meses após a colheita, as emissões dos três gases foram similares, independentemente da quantidade de palha. Remover a palha de cana-de-açúcar não aumenta as emissões de GEE do solo em comparação ao manejo sem retirada da palha da superfície. Contudo, estudos adicionais são necessários para investigar os efeitos sobre a produtividade de cana-de-açúcar, sobre a erosão e sobre outros atributos do solo.Palavras-chave: dióxido de carbono, metano, óxido nitroso, etanol de segunda geração, resíduo vegetal. Greenhouse gases emissions due to sugarcane trash on the soil AbstractBiofuels are important to reduce greenhouse gases (GHGs) emissions to atmosphere. In Brazil, the main biofuel is ethanol from sugarcane. Beyond stalk, sugarcane sheets are also stating to be used to produce second generation ethanol. The objective of this work was evaluate soil GHGs (CO 2 , CH 4 and N 2 O) emissions induced by sugarcane trash on soil surface. Three experiments were done in an Oxisol, in Piracicaba region, taking in account three periods: immediately after sugarcane harvest, six and twelve months after harvest. In each experiment, we evaluated the effects of three sugarcane trash rates (0%, 50% and 100% of the quantity available at soil surface). Immediately after harvest, CO 2 and CH 4 emissions increased linearly with trash rate on soil surface. Six months after harvest there were CH 4 consumption by soil as trash on surface increased. Twelve months after harvest, emissions of the three gases were similar in all trash rates. Removing sugarcane straw from soil surface do not increase soil GHGs emissions as compared to the current management, in which 100% of trash is maintained on the soil surface. However, other studies are needed to investigate its effects under sugarcane yield, soil erosion and under other soil attributes.

RESUMOO patchouli (Pogostemon cablin), pertencente à família Lamiaceae, possui grande interesse comercial pela presença de óleo essencial, contido nas folhas, que é utilizado principalmente na indústria de perfumaria. O objetivo deste trabalho foi avaliar o enraizamento de estacas de patchouli, de acordo com o número de folhas e a região do ramo utilizado para a estaquia. As estacas de patchouli foram obtidas de plantas cultivadas no município de Joinville-SC. Foram instalados dois experimentos com delineamentos experimentais inteiramente casualizados e cinco repetições. No primeiro experimento, foi avaliada a presença de folhas (estacas sem folhas, estacas com uma folha e estacas com duas folhas) usando estacas medianas. No segundo experimento, foi avaliada a posição de coleta das estacas no caule, testando estacas basais, medianas e apicais. As estacas apicais e medianas foram preparadas com um par de folhas e as estacas basais sem folhas. As avaliações foram realizadas aos 30 dias após a estaquia. Estacas apicais e medianas não diferiram entre si, quanto à porcentagem de enraizamento (93,7% e 83,7%, respectivamente) e comprimento médio das três maiores raízes por estaca (11,1 cm e 10,2 cm, respectivamente), sendo superiores em relação às estacas basais. O número de raízes emitidas por estaca decresceu significativamente das estacas apicais (35,5) para as basais (7,3). Estacas com duas folhas e uma folha apresentaram maior porcentagem de enraizamento (71,7% e 51,7%, respectivamente) e de brotação (78,4% e 44,9%, respectivamente) do que as estacas sem folhas. Para o número de raízes emitidas por estaca, aquelas que continham duas folhas (25,7) foram superiores às com uma folha (15,6) e às sem folhas (2,7). Recomenda-se para a propagação por estaquia do patchouli o uso de estacas apicais ou medianas com duas folhas.Palavras-chave: Pogostemon cablin; estaquia; propagação vegetativa. ABSTRACTPatchouli (Pogostemon cablin) belongs to Lamiaceae family and has great comercial interest due the essential oil production in leaves which is used mainly in the perfumary industry. The objective of this work was to evaluate the root formation of patchouli according to leaf and stem cutting positions. The plant material was obtained from Joinville (SC). Two experiments were carried out using a complete randomized design with five replications. The first experiment investigated the effect of leaves on stem cuttings (stems without leaves and with one and two leaves) obtained from medium region of the stems. The second experiment compared the effect of the region of the stem as a source of cuttings and the treatments included basal, medium and apical regions. The stems from apical and medium region had one pair of leaves and the stem from basal region had no leaves. After 30 days the experiment results were evaluated. Stem cuttings collected from the apical and medium regions of the stem showed no statistical difference of rooting percentage (93,7% and 83,7%, respectively) and the length of the three great roots of the cuttings ...