• Authors:
    • Fujisaki,K.
    • Perrin,A. S.
    • Desjardins,T.
    • Bernoux,M.
    • Balbino,L. C.
    • Brossard,M.
  • Source: Global Change BIology
  • Volume: 21
  • Issue: 7
  • Year: 2015
  • Summary: The impact of deforestation on soil organic carbon (SOC) stocks is important in the context of climate change and agricultural soil use. Trends of SOC stock changes after agroecosystem establishment vary according to the spatial scale considered, and factors explaining these trends may differ sometimes according to meta-analyses. We have reviewed the knowledge about changes in SOC stocks in Amazonia after the establishment of pasture or cropland, sought relationships between observed changes and soil, climatic variables and management practices, and synthesized the delta 13C measured in pastures. Our dataset consisted of 21 studies mostly synchronic, across 52 sites (Brazil, Colombia, French Guiana, Suriname), totalling 70 forest-agroecosystem comparisons. We found that pastures ( n=52, mean age=17.6 years) had slightly higher SOC stocks than forest (+6.83.1 %), whereas croplands ( n=18, mean age=8.7 years) had lower SOC stocks than forest (-8.52.9 %). Annual precipitation and SOC stocks under forest had no effect on the SOC changes in the agroecosystems. For croplands, we found a lower SOC loss than other meta-analyses, but the short time period after deforestation here could have reduced this loss. There was no clear effect of tillage on the SOC response. Management of pastures, whether they were degraded/nominal/improved, had no significant effect on SOC response. delta 13C measurements on 16 pasture chronosequences showed that decay of forest-derived SOC was variable, whereas pasture-derived SOC was less so and was characterized by an accumulation plateau of 20 Mg SOC ha -1 after 20 years. The large uncertainties in SOC response observed could be derived from the chronosequence approach, sensitive to natural soil variability and to human management practices. This study emphasizes the need for diachronic and long-term studies, associated with better knowledge of agroecosystem management.
  • Authors:
    • Hall,S. J.
    • Silver,W. L.
    • Timokhin,V. I.
    • Hammel,K. E.
  • Source: Global Change Biology
  • Volume: 21
  • Issue: 7
  • Year: 2015
  • Summary: Lignin mineralization represents a critical flux in the terrestrial carbon (C) cycle, yet little is known about mechanisms and environmental factors controlling lignin breakdown in mineral soils. Hypoxia is thought to suppress lignin decomposition, yet potential effects of oxygen (O 2) variability in surface soils have not been explored. Here, we tested the impact of redox fluctuations on lignin breakdown in humid tropical forest soils during ten-week laboratory incubations. We used synthetic lignins labeled with 13C in either of two positions (aromatic methoxyl or propyl side chain C beta) to provide highly sensitive and specific measures of lignin mineralization seldom employed in soils. Four-day redox fluctuations increased the percent contribution of methoxyl C to soil respiration relative to static aerobic conditions, and cumulative methoxyl-C mineralization was statistically equivalent under static aerobic and fluctuating redox conditions despite lower soil respiration in the latter treatment. Contributions of the less labile lignin C beta to soil respiration were equivalent in the static aerobic and fluctuating redox treatments during periods of O 2 exposure, and tended to decline during periods of O 2 limitation, resulting in lower cumulative C beta mineralization in the fluctuating treatment relative to the static aerobic treatment. However, cumulative mineralization of both the C beta- and methoxyl-labeled lignins nearly doubled in the fluctuating treatment relative to the static aerobic treatment when total lignin mineralization was normalized to total O 2 exposure. Oxygen fluctuations are thought to be suboptimal for canonical lignin-degrading microorganisms. However, O 2 fluctuations drove substantial Fe reduction and oxidation, and reactive oxygen species generated during abiotic Fe oxidation might explain the elevated contribution of lignin to C mineralization. Iron redox cycling provides a potential mechanism for lignin depletion in soil organic matter. Couplings between soil moisture, redox fluctuations, and lignin breakdown provide a potential link between climate variability and the biochemical composition of soil organic matter.
  • Authors:
    • Oluwole,O. S. A.
  • Source: Climatic Change
  • Volume: 131
  • Issue: 2
  • Year: 2015
  • Summary: Konzo epidemics occur during droughts in East, Central, and Southern Africa, where the population depends almost exclusively on poorly processed cassava. Warm phases of El Nino-Southern Oscillation (ENSO) and Pacific decadal Oscillation (PDO) are associated with droughts in these areas of Africa, but with increase rainfall in South America. To further understanding of the relationship of droughts, cassava production, and konzo epidemics, this study was done to determine if there is coherence of spectra of ENSO, PDO and cassava production. Annual time series of cassava production in Tanzania and Brazil, multivariate ENSO index (MEI), and the Pacific Decadal Oscillation index (PDO) from 1961-2013 were compared. Wavelet and cross wavelet analyses of cassava production, ENSO, and PDO were performed. Warm phases of ENSO and PDO were associated with high cassava production in Tanzania, but with low cassava production in Brazil. Spectrogram of cassava showed significantly high production at periodicities of 3-9 years in Tanzania, but with significantly low production at periodicities of 2-6 years in Brazil. Cross wavelet spectrograms showed coherence of cassava production, ENSO and PDO in Tanzania and Brazil. Time-varying cyclical cassava production in Tanzania and Brazil are coupled to ENSO and PDO modes. Occurrence of droughts, high cassava production, and konzo epidemics in Tanzania are attributable to the impact of climate variability, which should be the focus of public health policies to control konzo epidemics.
  • Authors:
    • Zhang,K.
    • Castanho,A. D. de A.
    • Galbraith,D. R.
    • Moghim,S.
    • Levine,N. M.
    • Bras,R. L.
    • Coe,M. T.
    • Costa,M. H.
    • Malhi,Y.
    • Longo,M.
    • Knox,R. G.
    • McKnight,S.
    • Wang,J. F.
    • Moorcroft,P. R.
  • Source: Global Change Biology
  • Volume: 21
  • Issue: 7
  • Year: 2015
  • Summary: There is considerable interest in understanding the fate of the Amazon over the coming century in the face of climate change, rising atmospheric CO 2 levels, ongoing land transformation, and changing fire regimes within the region. In this analysis, we explore the fate of Amazonian ecosystems under the combined impact of these four environmental forcings using three terrestrial biosphere models (ED2, IBIS, and JULES) forced by three bias-corrected IPCC AR4 climate projections (PCM1, CCSM3, and HadCM3) under two land-use change scenarios. We assess the relative roles of climate change, CO 2 fertilization, land-use change, and fire in driving the projected changes in Amazonian biomass and forest extent. Our results indicate that the impacts of climate change are primarily determined by the direction and severity of projected changes in regional precipitation: under the driest climate projection, climate change alone is predicted to reduce Amazonian forest cover by an average of 14%. However, the models predict that CO 2 fertilization will enhance vegetation productivity and alleviate climate-induced increases in plant water stress, and, as a result, sustain high biomass forests, even under the driest climate scenario. Land-use change and climate-driven changes in fire frequency are predicted to cause additional aboveground biomass loss and reductions in forest extent. The relative impact of land use and fire dynamics compared to climate and CO 2 impacts varies considerably, depending on both the climate and land-use scenario, and on the terrestrial biosphere model used, highlighting the importance of improved quantitative understanding of all four factors - climate change, CO 2 fertilization effects, fire, and land use - to the fate of the Amazon over the coming century.
  • Authors:
    • Apolinario,V. X. O.
    • Dubeux,J. C. B.
    • Lira,M. A.
    • Ferreira,R. L. C.
    • Mello,A. C. L.
    • Santos,M. V. F.
    • Sampaio,E. V. S. B.
    • Muir,J. P.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 5
  • Year: 2015
  • Summary: Warm-climate grasslands can be degraded by overgrazing and reduced soil fertility. However, legume trees integrated into these systems (silvopasture) can provide long-term marketable wood for sale and add N to the system. In addition, tree legumes can improve livestock diet by providing high crude protein forage. Our research assessed biomass and N accumulation by tree legumes: gliricidia [ Gliricidia sepium (Jacq.) Kunthe] and sabia ( Mimosa caesalpiniifolia Benth.) grown in conventionally grazed signal grass ( Brachiaria decumbens Stapf) pasture. The seedlings were planted in 2008 and growth rates were measured in 2012 and 2013. One year after the seedlings were planted, in July 2009, the pastures were grazed. Aboveground biomass doubled from 25 to 50 Mg ha -1 between February 2012 and August 2013. The thickest branches contributed the most ( p≤0.05) biomass: 58% for gliricidia and 54% for sabia. Leaves represented the smallest ( p≤0.05) fraction: 7 to 13% for gliricidia and 4 to 14% for sabia. Leaf and branch nutrient concentrations varied little ( p>0.05) between species and sampling periods. Gliricidia leaf N ranged from 33.6 to 38.0 g kg -1, while sabia leaf N ranged from 26.9 to 38.5 g kg -1. Biologically fixed N in leaves ranged from 30 to 121 kg ha -1. Sabia branches had less moisture and greater lignin, density, and gross calorific power than gliricidia. While thicker branches represent most of the aboveground tree biomass, leaves and thin branches have greater N concentration, representing an important return pathway to the soil.
  • Authors:
    • Brunetto, G.
    • Tassinari, A.
    • Vidal, R. F.
    • Lourenzi, C. R.
    • Lorensini, F.
    • Ferreira, P. A.
    • Ceretta, C. A.
    • Conti, L.
  • Source: Brazilian Journal of Soil Science
  • Volume: 39
  • Issue: 3
  • Year: 2015
  • Summary: The application of pig slurry rates and plant cultivation can modify the soil phosphorus (P) content and distribution of chemical species in solution. The purpose of this study was to evaluate the total P, available P and P in solution, and the distribution of chemical P species in solution, in a soil under longstanding pig slurry applications and crop cultivation. The study was carried out in soil columns with undisturbed structure, collected in an experiment conducted for eight years in the experimental unit of the Universidade Federal de Santa Maria (UFSM), Santa Maria (RS). The soil was an Argissolo Vermelho distrofico arenico (Typic Hapludalf), subjected to applications of 0, 20, 40, and 80 m(3) ha(-1) pig slurry. Soil samples were collected from the layers 0-5, 5-10, 10-20, 20-30, 30-40, and 40-60 cm, before and after black oat and maize grown in a greenhouse, for the determination of available P, total P and P in the soil solution. In the solution, the concentration of the major cations, anions, dissolved organic carbon (DOC), and pH were determined. The distribution of chemical P species was determined by software Visual Minteq. The 21 pig slurry applications increased the total P content in the soil to a depth of 40 cm, and the P extracted by Mehlich-1 and from the solution to a depth of 30 cm. Successive applications of pig slurry changed the balance between the solid and liquid phases in the surface soil layers, increasing the proportion of the total amount of P present in the soil solution, aside from changing the chemical species in the solution, reducing the percentage complexed with Al and increasing the one complexed with Ca and Mg in the layers 0-5 and 5-10 cm. Black oat and maize cultivation increased pH in the solution, thereby increasing the proportion of HPO42- and reducing H2PO4- species.
  • Authors:
    • Ghini,Raquel
    • Torre-Neto,Andre
    • Dentzien,Anamaria F. M.
    • Guerreiro-Filho,Oliveiro
    • Iost,Regiane
    • Patricio,Flavia R. A.
    • Prado,Jeanne S. M.
    • Thomaziello,Roberto A.
    • Bettiol,Wagner
    • DaMatta,Fabio M.
  • Source: Climatic Change
  • Volume: 132
  • Issue: 2
  • Year: 2015
  • Summary: Despite the importance of coffee as a globally traded commodity and increasing concerns about risks associated with climate change, there is virtually no information about the effects of rising atmospheric [CO2] on field-grown coffee trees. This study shows the results of the first 2 years of an innovative experiment. Two commercial coffee cultivars (Catuai and Obat) were grown using the first free-air CO2 enrichment (FACE) facility in Latin America (ClimapestFACE). Plants of both cultivars maintained relatively high photosynthetic rates, water-use efficiency, increased growth and yield under elevated [CO2]. Harvestable crop yields increased 14.6 % for Catuai and 12.0 % for Obat. Leaf N content was lower in Obat (5.2 %) grown under elevated [CO2] than under ambient [CO2]; N content was unresponsive to elevated [CO2] in Catuai. Under elevated [CO2] reduced incidence of leaf miners (Leucoptera coffeella) occurred on both coffee cultivars during periods of high infestation. The percentage of leaves with parasitized and predated mines increased when leaf miner infestation was high, but there was no effect of elevated [CO2] on the incidence of natural enemies. The incidence of rust (Hemileia vastatrix) and Cercospora leaf spot (Cercospora coffeicola) was low during the trial, with maximum values of 5.8 and 1 %, respectively, and there was no significant effect of [CO2] treatments on disease incidence. The fungal community associated with mycotoxins was not affected by the treatments.
  • Authors:
    • Borghi, E.
    • Nascente, A. S.
    • Crusciol, C. A. C.
    • Soratto, R. P.
    • Martins, P. O.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 6
  • Year: 2015
  • Summary: In tropical regions with dry winters, low plant biomass accumulation during the period between spring-summer crop cultivations can negatively impact soil resources and make the no-till (NT) system unsustainable. Incorporating palisadegrass [ Urochloa brizantha (Hochst. Ex A. Rich.) R.D. Webster] [syn. Brachiaria brizantha (Hochst. Ex A. Rich) Stapf] in traditional grain production areas could improve soil quality for subsequent crops and lead to positive effects on grain yield. The objective of this study was to evaluate the effects of growing palisadegrass on soil fertility, plant nutrition, and grain yield of subsequent cash crops in a tropical region. The experiment was performed in southeastern Brazil in plots that were grown for two consecutive growing seasons (2002-2003 and 2003-2004) with either monocropped corn ( Zea mays L.) or corn intercropped with palisadegrass. An initial evaluation of soil fertility was performed in November 2004 when the land was either fallow (following monocropped corn) or covered by palisadegrass (intercropped areas). After the preceding treatments, the following crops were cultivated: soybean [ Glycine max (L.) Merr.] during the 2004-2005 and 2005-2006 spring-summer, white oat ( Avena sativa L.) during the 2005 and 2006 fall-winter, and corn during the 2006-2007 spring-summer. Intercropping palisadegrass with corn increased the soil fertility compared to monocropped corn. Soybean, white oat, and corn all had higher leaf macronutrient concentrations and grain yields in previously intercropped areas than in monocropped areas. Therefore, the periodic, short-term incorporation of a perennial forage grass, such as palisadegrass, as a cover crop is recommended to increase grain production and to improve the soil fertility of grain-production areas.
  • Authors:
    • Nuesslein, K.
    • Cerri, C.
    • Feigl, B.
    • Lammel, D.
  • Source: Frontiers in Microbiology
  • Volume: 6
  • Year: 2015
  • Summary: Ecological processes regulating soil carbon (C) and nitrogen (N) cycles are still poorly understood, especially in the world's largest agricultural frontier in Southern Amazonia. We analyzed soil parameters in samples from pristine rainforest and after land use change to pasture and crop fields, and correlated them with abundance of functional and phylogenetic marker genes (amoA, nirK, nirS, norB, nosZ, nifH, mcrA, pmoA, and 16S/18S rRNA). Additionally, we integrated these parameters using path analysis and multiple regressions. Following forest removal, concentrations of soil C and N declined, and pH and nutrient levels increased, which influenced microbial abundances and biogeochemical processes. A seasonal trend was observed, suggesting that abundances of microbial groups were restored to near native levels after the dry winter fallow. Integration of the marker gene abundances with soil parameters using path analysis and multiple regressions provided good predictions of biogeochemical processes, such as the fluxes of NO3, N20, CO2, and CH4. In the wet season, agricultural soil showed the highest abundance of nitrifiers (amoA) and Archaea, however, forest soils showed the highest abundances of denitrifiers (nirK, nosZ) and high N, which correlated with increased N20 emissions. Methanogens (mcrA) and methanotrophs (pmoA) were more abundant in forest soil, but methane flux was highest in pasture sites, which was related to soil compaction. Rather than analyzing direct correlations, the data integration using multivariate tools provided a better overview of biogeochemical processes. Overall, in the wet season, land use change from forest to agriculture reduced the abundance of different functional microbial groups related to the soil C and N cycles; integrating the gene abundance data and soil parameters provided a comprehensive overview of these interactions. Path analysis and multiple regressions addressed the need for more comprehensive approaches to improve our mechanistic understanding of biogeochemical cycles.
  • Authors:
    • Martins,B. H.
    • Araujo-Junior,C. F.
    • Miyazawa,M.
    • Vieira,K. M.
    • Milori,D. M. B. P.
  • Source: Soil and Tillage Research
  • Volume: 153
  • Year: 2015
  • Summary: Soil organic matter (SOM) plays an important role for soil quality and productivity maintenance, acting as energy source, promoting biological diversity, enhancing terrestrial ecosystems composition. This study assessed the effects of long-term weed control and cover crops between coffee rows on SOM quality in a very clayey (80dagkg-1 of clay) Typic Haplorthox (Dystroferric Red Latosol) from State of Paraná, Southern Brazil. Seven weed control and cover crops were assessed between coffee rows: (i) hand weeding-HAWE; (ii) portable mechanical mower-PMOW; (iii) pré+post-emergence herbicides-HERB; (iv) peanut horse (Arachis hypogeae) cover crop-GMAY; (v) dwarf mucuna (Mucuna deeringiana) cover crop-GMMA; (vi) no-weed control between coffee row-SCAP; (vii) weed check-CONT. Soil samples were collected in the center of the inter-rows between coffee trees at four depths: 0-10cm, 10-20cm, 20-30cm, and 30-40cm. SOM quality assessment included total soil organic carbon (SOC) content and organic matter humification degree (HFIL) by laser-induced fluorescence spectroscopy (LIFS). C content was up to 26% higher for SCAP and CONT samples, compared to the other field conditions, denoting influence of plant material accumulation at top soil (0-10cm). Higher HFIL results (up to 47%) were observed at deeper layers, inferring incidence of less humified/labile structures at top soil, and condensed/recalcitrant character for organic matter at depth, regardless of cover crops and weed control method considered. In terms of weed density it was observed a higher negative impact on weed growth in areas under GMMA cover crop (decrease of 90.8% in weed density). The behavior may be attributed to the chemical composition of the species, ultimately leading to possible occurrence of allelopathic phenomenon. © 2015 Elsevier B.V.