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In Mexico, pasture degradation is associated with extensive pastures; additionally, under these conditions, livestock activities contribute considerably to greenhouse gas (GHG) emissions. Among the options to improve grazing systems and reduce GHG emissions, silvopastoral systems (SPS) have been recommended. The objectives of this work were to quantify the N outflow in a soil-plant-animal interface, as well as the CH4 emissions and milk production in an SPS with woody legumes (Leucaena leucocephala) that is associated with stargrass (Cynodon nlemfuensis). This was then compared with stargrass in a monoculture system (MS) in the seasons (dry and rainy period) over a two-year period. Dung was collected from the animals of each of the grazing systems and applied fresh to the land plots. Fresh dung and urine were collected from the cows of each grazing system and were applied to the experimental plots. In addition, the soil CH4 and N2O contents were measured to quantify the emissions. Average milk yield by seasons was similar: MS (7.1 kg per animal unit (AU)/day-1) and SPS (6.31 kg per AU/day-1). Cows in the MS had a mean N intake of 171.9 g/UA day-1 without seasonal variation, while the SPS animals' mean N intake was 215.7 g/UA day-1 for both seasons. For the urine applied to soil, the N2O outflow was higher in the MS (peak value = 1623.9 µg N-N2O m-2 h-1). The peak value for the SPS was 755.9 µg of N-N2O m-2 h-1. The N2O emissions were higher in the rainy season (which promotes denitrification). The values for the feces treatment were 0.05% (MS) and 0.01% (SPS). The urine treatment values were 0.52% (MS) and 0.17% (SPS). The emissions of CH4 showed that the feces of the SPS systems resulted in a higher accumulation of gas in the rainy season (29.8 g C ha-1), followed by the feces of the MS system in the dry season (26.0 g C ha-1). Legumes in the SPS helped to maintain milk production, and the N2O emissions were lower than those produced by the MS (where the pastures were fertilized with N).

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The introduction of a forage legume into a tropical pasture should decrease the need for N fertilizer, provided biological N2 fixation (BNF) contributes enough to compensate for exported N. Macrotyloma axillare (perennial horsegram) is a suitable legume for composing mixed pastures, and our hypothesis is that the isolation of indigenous rhizobia from roots and rhizosphere is the way of achieving an efficient inoculant to maximize BNF to the legume. Nodules and rhizosphere soil taken from M. axillare grown in a mixed pasture with palisade grass were sampled and used in a trap host assay using Leonard jars containing a mixture of vermiculite and sand. A total of ten bacteria were initially isolated using this technique. The isolates were then used in two experiments to evaluate the inoculation responses on the perennial horsegram in greenhouse conditions to which nodulation, plant growth, and shoot N accumulation were measured. Phylogenetic analyses based on 16S rRNA and recA placed all strains within genus Bradyrhizobium, some of them not previously described. The best strain provided more than 120 nodules and more than 65 mg of nodules per plant. Strain BR14182 was considered the most promising given the high dry matter and N accumulation in plant shoots. This study provides the first analysis of Bradyrhizobium diversity nodulating M. axillare in Brazil and provided evidence of the role of inoculation in incrementing the plant-rhizobium symbiosis in a forage legume.

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While most soils in periglacial environments present high fluxes of CO2 (FCO2), CH4 (FCH4), and N2O (FN2O), few of them have a tendency to drain greenhouse gases from the atmosphere. This study aimed to assess greenhouse gas fluxes at different sub-Antarctic sites and time periods (at the beginning of thaw and height of summer). To investigate the time of year effect on greenhouse gas emissions, FCO2, FCH4, and FN2O were measured at two sites tundra-covered (Ti and Th) and Nothofagus forest soil (Nf) on Monte Martial, at the southernmost tip of South America, Tierra del Fuego, Argentina. FCO2 ranged from 96.33 to 225.72 µg CO2 m-2 s-1 across all sites and periods, showing a positive correlation with soil temperature (Ts) (4.1 and 8.2 °C, respectively) (r2 > 0.7; p < 0.05). The highest values of FCO2 were found at Ti and Th (728.2 and 662.64 µg CO2 m-2 s-1, respectively), which were related to higher temperatures (8.2 and 8.6 °C, respectively) when compared to those of Nf. For FCH4, the capture (drain) occurred during both periods at Nf (-26 and -79 µg C-CH4 m-2 h-1) as well as Ti and Th (-21 and 12 µg C-CH4 m-2 h-1, respectively). FN2O also presented low values during both periods and showed a tendency to drain N2O from the atmosphere, especially at Nf (-2 µg N-N2O m-2 h-1). In addition, FN2O was slightly positive for Ti and Th (0.3 and 0.55 µg N-N2O m-2 h-1, respectively). Soil moisture did not show a correlation (p > 0.05) with the measured greenhouse gas fluxes. A scenario of increased temperatures might result in changes in the balance between the emissions and drains of these gases from soils, leading to higher emission values of CH4 and N2O, especially for tundra covered soils (Ti and Th), where the highest average fluxes and thermohydric variations were observed over the year.

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Land-use change (LUC) in Brazil has important implications on global climate change, ecosystem services and biodiversity, and agricultural expansion plays a critical role in this process. Concerns over these issues have led to the need for estimating the magnitude and impacts associated with that, which are increasingly reported in the environmental assessment of products. Currently, there is an extensive debate on which methods are more appropriate for estimating LUC and related emissions and regionalized estimates are lacking for Brazil, which is a world leader in agricultural production (e.g. food, fibres and bioenergy). We developed a method for estimating scenarios of past 20-year LUC and derived CO2 emission rates associated with 64 crops, pasture and forestry in Brazil as whole and in each of its 27 states, based on time-series statistics and in accordance with most used carbon-footprinting standards. The scenarios adopted provide a range between minimum and maximum rates of CO2 emissions from LUC according to different possibilities of land-use transitions, which can have large impacts in the results. Specificities of Brazil, like multiple cropping and highly heterogeneous carbon stocks, are also addressed. The highest CO2 emission rates are observed in the Amazon biome states and crops with the highest rates are those that have undergone expansion in this region. Some states and crops showing large agricultural areas have low emissions associated, especially in southern and eastern Brazil. Native carbon stocks and time of agricultural expansion are the most decisive factors to the patterns of emissions. Some implications on LUC estimation methods and standards and on agri-environmental policies are discussed.

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This study aimed to quantify nitrous oxide (N2O) and methane (CH4) emission/sink response from sugar cane soil treated with fertilizer nitrogen (N) and vinasse applied separately or in sequence, the latter being investigated with regard to the time interval between applications for a possible effect on emissions. The study was carried out in a traditional area of unburned sugar cane in São Paulo state, Brazil. Two levels of N fertilization (0 and 100 kg N ha(-1)) with no added vinasse and combined with vinasse additions at different times (100 m(-3) ha(-1) at 3 and 15 days after N fertilization) were evaluated. Methane and N2O fluxes were monitored for 211 days. On average, the soil was a sink for CH4, which was not affected by the treatments. Emissions of N2O were induced by N fertilizer and vinasse applications. For ammonium sulfate, 0.6% of the added N was emitted as N2O, while for vinasse, this ranged from 1.0 to 2.2%. Changes in N2O fluxes were detected the day after application of vinasse on the N fertilized areas, but although the emission factor (EF) was 34% greater, the EF was not significantly different from fertilizer N alone. Nevertheless, we recommend to not apply vinasse after N fertilization to avoid boosting N2O emissions.

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