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We hypothesized that the age of loblolly pine stands influences soil methane (CH4) and nitrous oxide (N2O) emissions. This is a relevant topic to be studied in subtropical Brazil, where the pine plantation area is increasing considerably. We evaluated N2O and CH4 emissions for two years in a Ferralsol under loblolly pine (Pinus taeda L.) stands of 1, 9 and 18 year-olds and a native forest (NF). We calculated the net CO2eq emission by considering the N2O and CH4 emissions from soil and the carbon (C) accumulation as litter in the forest floor. The soil N2O emission reduced gradually over the loblolly pine cultivation years, whereas CH4 uptake rates showed no clear pattern. Soil N2O emission showed a positive relationship with soil temperature in NF, and with soil ammonium and nitrate intensities in the pine stands. Soil CH4 uptake was inversely related to water-filled pore space in the pine stands, but this relationship was not observed in NF. The soil CH4 uptake rate was 4.6 times higher (p < 0.10) in NF than the average uptake in loblolly pine stands. On the other hand, soil N2O emissions in 9 and 18-year-old stands were similar (p > 0.10) to those in NF (1.3 kg N ha-1 yr-1). Our results suggest that cultivation with loblolly pine for 18 years can reduce soil N2O emission, and the uptake of CH4 in this system offsets 17 % of N2O emissions. Furthermore, the C accumulation as litter in the forest floor of the mature pine stands (9- and 18-year-old) generated a net emission of -1.6 Mg CO2eq ha-1 yr-1, showing to be an expressive offsetting mechanism. Therefore, we conclude that aged loblolly forests can reach N2O emissions levels comparable to those of NF, and the C sequestration in these forests floor can significantly contribute to offset N2O emissions and act as sink for net atmospheric CO2eq.

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This study aimed at evaluating soil nitrous oxide (N2O) and methane (CH4) emissions from integrated farming systems. Soil N2O and CH4 fluxes were assessed in a subtropical Cambisol in southern Brazil, using manual static chambers, over two years, in five farming systems (cropland, livestock, integrated crop-livestock, integrated livestock-forestry, and integrated crop-livestock-forestry). The study was conducted in four growing seasons: summer-1, winter-1, summer-2, winter-2. Integrated farming systems had lower soil N2O emissions than livestock. The observed reduction was possibly due to lower water-filled pore space (WFPS) in soils under integrated systems (average 59.5-64.7%, vs 70.4% in livestock) as indicated by correlation (r = 0.74). Cropland, including cover-crops and maize, also had lower N2O emission (by 40%) relative to livestock, of levels similar to those observed in integrated systems. Methane was consumed in soil, but it was not affected by farming systems, and offset only ~1.4% of the N2O emissions. In the rainiest season of summer-2, the soil had the highest WFPS (on average 71.4%) and thus the highest N2O emission (on average 9.79 kg N2O-N ha-1 season-1) and the lowest CH4 consumption (on average - 0.40 kg CH4-C ha-1 season-1); while the opposite trend occurred in the driest season of winter-2 (on average 57.3% WFPS; 0.64 kg N2O-N ha-1 season-1 and -0.90 kg CH4-C ha-1 season-1). Integrated farming systems including crop-livestock, livestock-forestry and crop-livestock-forestry reduced soil N2O emissions relative to sole livestock by 27-40%, but did not affect CH4 emissions. Seasonal variations of precipitation, and therefore WFPS were driving factors of the N2O and CH4 emissions. Overall, integrated farming systems show the potential to mitigate soil N2O emission compared to livestock system.

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Amazonian rainforests, once thought to be pristine wilderness, are increasingly known to have been widely inhabited, modified, and managed prior to European arrival, by human populations with diverse cultural backgrounds. Amazonian Dark Earths (ADEs) are fertile soils found throughout the Amazon Basin, created by pre-Columbian societies with sedentary habits. Much is known about the chemistry of these soils, yet their zoology has been neglected. Hence, we characterized soil fertility, macroinvertebrate communities, and their activity at nine archeological sites in three Amazonian regions in ADEs and adjacent reference soils under native forest (young and old) and agricultural systems. We found 673 morphospecies and, despite similar richness in ADEs (385 spp.) and reference soils (399 spp.), we identified a tenacious pre-Columbian footprint, with 49% of morphospecies found exclusively in ADEs. Termite and total macroinvertebrate abundance were higher in reference soils, while soil fertility and macroinvertebrate activity were higher in the ADEs, and associated with larger earthworm quantities and biomass. We show that ADE habitats have a unique pool of species, but that modern land use of ADEs decreases their populations, diversity, and contributions to soil functioning. These findings support the idea that humans created and sustained high-fertility ecosystems that persist today, altering biodiversity patterns in Amazonia.

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Nitrous oxide (N2O) emissions from pasture-based livestock systems represent 34% of Brazil's agricultural greenhouse gas emissions. The forage species Brachiaria humidicola is known for its biological nitrification inhibition (BNI) capacity and N2O emissions reduction ability from urine patches under tropical conditions. However, there is little information about the effect of BNI on N2O emission and ammonia (NH3) volatilisation in the subtropics. This study aimed to: (i) evaluate the potential of Brachiaria humidicola, compared with Panicum maximum (Jacq. cv. Áries; guinea grass), a broadly used grass (with no BNI capacity), to reduce N2O emissions under subtropical conditions; (ii) determine the efficacy of nitrification inhibitor dicyandiamide (DCD) to decrease N2O emissions; and (iii) determine the effect of brachiaria and DCD application on NH3 volatilisation. A field experiment was carried out using a Cambisol, where cattle urine ± DCD was applied to brachiaria and guinea grass. Over the 67-day measurement period, cumulative N2O emissions were 20% lower from urine patches in the brachiaria treatment (1138 mg N m-2, Emission factor = 1.06%) compared to guinea grass (1436 mg N m-2, Emission factor = 1.33%) (P < .10). A greenhouse experiment, using pots with the same treatments as in the field experiment, suggested that this could have been due to lower soil nitrate levels under brachiaria forage compared to guinea grass, indicating that BNI could be a possible mechanism for lower N2O emissions from brachiaria. The DCD application was effective in both forage species, decreasing N2O emissions by 40-50% (P < .10) compared with the urine only treatment. Approximately 25% of the urine applied N was lost via NH3 volatilisation, however the NH3 loss was not affected by forage species or DCD application (P > .10). Overall, the results demonstrated that brachiaria and DCD use are strategies that can reduce N2O emissions from urine patches.

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Management systems to improve soil quality are essential for agricultural and environmental sustainability. We assessed the quality of soil management systems applied to a subtropical Acrisol in terms of the carbon management index (CMI), the stratification ratio for total organic carbon (SR-TOC) and light fraction of organic matter (SR-LF). In addition, we examined their relationship to chemical, physical and biological soil quality indicators, as well as to maize yield. The study was conducted on a long-term experiment (18 years) in southern Brazil involving two different systems [no tillage (NT) and conventional tillage (CT)], two cropping systems [black oat/maize (O/M) and black oat + vetch/maize + cowpea (OV/MC)] and two nitrogen fertilizer rates for maize (0 and 180 kg ha–1). Based on the three indices, the best managements for soil quality comprised NT (50-212 % better than CT), legume cover crops (10-47 % better than O/M) and N fertilization (8-33 % better than no fertilizer). All three indices proved accurate to assess the impact of soil management systems, especially SR-LF, which showed increased sensitivity and close relationships with chemical, physical and biological soil quality indicators. On the other hand, a poor relationship was observed between soil C indices and maize yield, which was improved only by legume cover crops and N fertilization. The results showed that the association of no-till system to an abundant supply of crop residues is key to ensure high soil quality and crop yields in humid subtropical regions.(AU)

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Management systems to improve soil quality are essential for agricultural and environmental sustainability. We assessed the quality of soil management systems applied to a subtropical Acrisol in terms of the carbon management index (CMI), the stratification ratio for total organic carbon (SR-TOC) and light fraction of organic matter (SR-LF). In addition, we examined their relationship to chemical, physical and biological soil quality indicators, as well as to maize yield. The study was conducted on a long-term experiment (18 years) in southern Brazil involving two different systems [no tillage (NT) and conventional tillage (CT)], two cropping systems [black oat/maize (O/M) and black oat + vetch/maize + cowpea (OV/MC)] and two nitrogen fertilizer rates for maize (0 and 180 kg ha–1). Based on the three indices, the best managements for soil quality comprised NT (50-212 % better than CT), legume cover crops (10-47 % better than O/M) and N fertilization (8-33 % better than no fertilizer). All three indices proved accurate to assess the impact of soil management systems, especially SR-LF, which showed increased sensitivity and close relationships with chemical, physical and biological soil quality indicators. On the other hand, a poor relationship was observed between soil C indices and maize yield, which was improved only by legume cover crops and N fertilization. The results showed that the association of no-till system to an abundant supply of crop residues is key to ensure high soil quality and crop yields in humid subtropical regions.

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Wetlands near urban centers may be more isolated areas and can be chosen for the disposal of bodies or used as a crime scene. The predominant soils in these areas usually have a high content of organic matter (OM), classified as Histosols. Soil organic matter (SOM) is composed of many different compounds that can be identified by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The study aimed to use Py-GC/MS to classify small amounts of organic soil in a forensic context. We sampled Histosols from five representative sites of Curitiba, Brazil. The molecular composition of the samples was determined by byPy-GC/MS. The factor analysis was carried out, and the factor scores showed a clear differentiation between the sites. Compounds indicative of relatively fresh plant material was separated from more recalcitrant and charred material. Py-GC/MS has the potential to be a useful tool to study the composition of SOM in Histosols to track the trace sample collected from a crime suspect.

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Organic soils are generally located in fluvial settings such as river floodplains that are commonly used for the disposal of bodies. Therefore, the aim of this study was to provide a protocol for the analysis of small amounts of organic soils for forensic purposes. The protocol was applied in five representative sites within the Curitiba metropolitan region (Brazil), with each site supplying four composite samples separated from one another by 3m. The soil samples were collected at a depth of 0 to 5cm. One gram of soil sample was used to determine the total elemental content and perform physical fractionation of the soil (>53µm and <53µm). For both soil size fractions, total C and N contents were determined, and the elements adsorbed to organic matter was determined only for the <53µm size fraction (Na-pyrophosphate extraction). Chemometric multivariate analyses were conducted for the total data set, where more than 77% of the variation was explained by the first three factors. It was determined that Ca, Ba, and Mg adsorbed to organic matter, and total Ba, Ca, K, Mg, Mo, and C contents were most important in sample groupings. As expected in forensic science, the five sites were efficiently distinguishable from each other and the four replicates collected at the same individual site were clearly grouped. This protocol for sampling, chemical analysis, and data treatment of organic soils can be used in real crime situations.

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Monitoring of heavy metal contamination plume in soils can be helpful in establishing strategies to minimize its hazardous impacts to the environment. The objective of this study was to apply a new approach of visualization, based on tridimensional (3D) images, of pseudo-total (extracted with concentrated acids) and exchangeable (extracted with 0.5 mol L(-1) Ca(NO3)2) lead (Pb) concentrations in soils of a mining and metallurgy area to determine the spatial distribution of this pollutant and to estimate the most contaminated soil volumes. Tridimensional images were obtained after interpolation of Pb concentrations of 171 soil samples (57 points × 3 depths) with regularized spline with tension in a 3D function version. The tridimensional visualization showed great potential of use in environmental studies and allowed to determine the spatial 3D distribution of Pb contamination plume in the area and to establish relationships with soil characteristics, landscape, and pollution sources. The most contaminated soil volumes (10,001 to 52,000 mg Pb kg(-1)) occurred near the metallurgy factory. The main contamination sources were attributed to atmospheric emissions of particulate Pb through chimneys. The large soil volume estimated to be removed to industrial landfills or co-processing evidenced the difficulties related to this practice as a remediation strategy.

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O fracionamento físico da matéria orgânica (MO) do solo é uma alternativa para a obtenção de frações lábeis utilizadas no cálculo do índice de manejo de carbono (IMC). O objetivo deste trabalho foi avaliar a eficiência do fracionamento físico granulométrico (53µm) e densimétrico, com soluções de iodeto de sódio 1,8Mg m-3 (NaI) ou politungstato de sódio 2,0Mg m-3 (PTS), na separação das frações lábeis (particulada e leve, respectivamente) da MO e o seu uso na estimativa do IMC. Amostras da camada de 0-20cm de um Argissolo Vermelho sob preparo convencional (PC) e plantio direto (PD), combinados com dois sistemas de culturas (aveia/milho e aveia+ervilhaca/milho+caupi), foram avaliadas quanto ao estoque de carbono orgânico total (COT), e nas frações particulada (COP) e leve (C-FL) da MO. No fracionamento físico densimétrico, com a utilização de NaI, foi recuperado menos C-FL em relação ao uso de PTS. A recuperação de COP no fracionamento granulométrico foi intermediária entre a recuperação de FL-NaI e de FL-PTS. O IMC com os dados do fracionamento granulométrico apresentou elevada correlação com o IMC dos dados de fracionamento densimétrico (NaI e PTS), havendo porém uma subestimação dos resultados com o uso de NaI. Os sistemas de manejo sem revolvimento do solo e com maior aporte de resíduos vegetais resultaram em maior IMC, tanto pelo aumento do índice de labilidade quanto do índice de estoque de carbono. O IMC a partir de frações físicas densimétricas da MO demonstra ser um índice eficiente na discriminação de sistemas de manejo, podendo ser utilizado na avaliação das práticas de manejo do solo.

The physical fractionation of soil organic matter (SOM) is an alternative in assessing the amount of labile fraction that is used to calculate the carbon management index (CMI). The objective this research was to assess the efficiency of particle-size physical fractionation, (53-µm mesh), and density physical fractionation, with sodium iodide 1.8Mg m-3 (NaI) or sodium polytungstate 2.0Mg m-3 (PTS) solutions, at recovering SOM labile fractions (particulate and light, respectively) and at estimating the CMI. Soil samples of the 0-20cm layer of a sandy clay loam Acrisol under conventional tillage (CT) and no-tillage (NT) combined with two cropping systems (oat/maize and oat+vetch/maize+cowpea) were analyzed for stocks of total organic carbon (TOC), particulate organic carbon fraction (POC) and light fraction carbon (LF-C). In density physical fractionation, with the use of NaI was recovered less LF-C than PTS. The recovery of POC by particle-size fractionation was intermediate between the recovery of NaI-LF and PTS-LF. The CMI calculated after particle-size fractionation showed high correlation with CMI after density fractionation with NaI or PTS, although results were rather underestimated with NaI. Conservation management systems without soil disturbance and with higher crop residue addition enhanced the CMI, because of increments of both lability index and carbon pool index. The CMI based on SOM physical densimetrical fraction shows evidence of being and efficient index to discriminate management systems that can be used to assess soil management practices.

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