Resumo A concentração de gases de efeito estufa (GEE) na atmosfera tem aumentado acentuadamente desde a revolução industrial, o que levou a intensificação do efeito estufa e consequentemente vem causando o aquecimento global. A análise espacial de tendências permite observar as mudanças no comportamento e determinar em quais regiões uma determinada variável vem sofrendo mudanças ao longo do tempo. Diante disso, o objetivo do presente trabalho foi analisar as tendências temporais da precipitação e da temperatura média no Brasil, utilizando o método Contextual Mann-Kendall (CMK), utilizando dados espacialmente distribuídos elaborados pelo Climatic Research Unit (CRU), entre os anos 1961 e 2011. A umidade relativa e a evapotranspiração foram analisadas no intuito de auxiliar na interpretação dos resultados da precipitação e temperatura. Os resultados mostraram tendências não significativas em mais de 70% do território brasileiro em todos os meses na precipitação, porém a temperatura média apresentou tendência positiva significativa em grande parte do Brasil ao longo de todo ano. Em geral, a evapotranspiração apresentou um comportamento diretamente proporcional à temperatura, enquanto que a umidade relativa apresentou comportamento inversamente proporcional. A continuidade dessas tendências poderá resultar em impactos na agricultura e no ciclo hidrológico, e consequentemente para a fauna e flora e para a população.

Abstract. In this paper we calculated soil carbon stocks in Brazil studying 17 paired sites where soil stocks were determined in native vegetation, pastures and crop-livestock systems (CPS), and in other regional samplings encompassing more than 100 pasture soils, from 6.58 to 31.53 • S, involving three major Brazilian biomes: Cerrado, Atlantic Forest, and the Pampa. The average native vegetation soil carbon stocks at 10, 30 and 60 cm soil depth were equal to approximately 29, 64, and 92 Mg ha −1 , respectively. In the paired sites, carbon losses of 7.5 Mg ha −1 and 11.6 Mg ha −1 in CPS systems were observed at 10 cm and 30 cm soil depths, respectively. In pasture soils, carbon losses were similar and equal to 7.5 Mg ha −1 and 11.0 Mg ha −1 at 10 cm and 30 cm soil depths, respectively. Differences at 60 cm soil depth were not significantly different between land uses. The average soil δ 13 C under native vegetation at 10 and 30 cm depth were equal to −25.4 ‰ and −24.0 ‰, increasing to −19.6 ‰ and −17.7 ‰ in CPS, and to −18.9 ‰, and −18.3 ‰ in pasture soils, respectively; indicating an increasing contribution of C 4 carbon in these agrosystems. In the regional survey of pasture soils, the soil carbon stock at 30 cm was equal to approximately 51 Mg ha −1 , with an average δ 13 C value of −19.6 ‰. Key controllers of soil carbon stock in pasture sites were sand content and mean annual temperature. Collectively, both could explain approximately half of the variance of soil carbon stocks. When pasture soil carbon stocks were compared with the average soil carbon stocks of native vegetation estimated for Brazilian biomes and soil types by Bernoux et al. (2002) there was a carbon gain of 6.7 Mg ha −1 , which is equivalent to a carbon gain of 15 % compared to the carbon soil stock of the native vegetation. The findings of this study are consistent with differences found between regional comparisons like our pasture sites and plot-level paired study sites in estimating soil carbon stocks changes due to land use changes.

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Abstract. In this paper, soil carbon, nitrogen and phosphorus concentrations and stocks were investigated in agricultural and natural areas in 17 plot-level paired sites and in a regional survey encompassing more than 100 pasture soils In the paired sites, elemental soil concentrations and stocks were determined in native vegetation (forests and savannas), pastures and crop-livestock systems (CPSs). Nutrient stocks were calculated for the soil depth intervals 0-10, 0-30, and 0-60 cm for the paired sites and 0-10, and 0-30 cm for the pasture regional survey by sum stocks obtained in each sampling intervals (0-5, 5-10, 10-20, 20-30, 30-40, 40-60 cm). Overall, there were significant differences in soil element concentrations and ratios between different land uses, especially in the surface soil layers. Carbon and nitrogen contents were lower, while phosphorus contents were higher in the pasture and CPS soils than in native vegetation soils. Additionally, soil stoichiometry has changed with changes in land use. The soil C : N ratio was lower in the native vegetation than in the pasture and CPS soils, and the carbon and nitrogen to available phosphorus ratio (P ME ) decreased from the native vegetation to the pasture to the CPS soils. In the plotlevel paired sites, the soil nitrogen stocks were lower in all depth intervals in pasture and in the CPS soils when compared with the native vegetation soils. On the other hand, the soil phosphorus stocks were higher in all depth intervals in agricultural soils when compared with the native vegetation soils. For the regional pasture survey, soil nitrogen and phosphorus stocks were lower in all soil intervals in pasture soils than in native vegetation soils. The nitrogen loss with cultivation observed here is in line with other studies and it seems to be a combination of decreasing organic matter inputs, in cases where crops replaced native forests, with an increase in soil organic matter decomposition that leads to a decrease in the long run. The main cause of the increase in soil phosphorus stocks in the CPS and pastures of the plot-level paired site seems to be linked to phosphorus fertilization by mineral and organics fertilizers. The findings of this paper illustrate that land-use changes that are currently common in Brazil alter soil concentrations, stocks and elemental ratios of carbon, nitrogen and phosphorus. These changes could have an impact on the subsequent vegetation, decreasing soil carbon and increasing nitrogen limitation but alleviating soil phosphorus deficiency.

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