• Authors:
    • Pidgeon, N. F.
    • Capstick, S. B.
  • Source: Research Article
  • Volume: 122
  • Issue: 4
  • Year: 2014
  • Summary: It has been argued that public doubts about climate change have been exacerbated by cold weather events seen as a form of disconfirming evidence for anticipated 'warming'. Although a link between perceptions of climate and weather is well-established, such assumptions have not been empirically tested. Here we show, using nationally representative data, that directly following a period of severe cold weather in the UK, three times as many people saw these events as pointing towards the reality of climate change, than as disconfirming it. This we argue was a consequence of these cold winters being incorporated into a conceptualisation of extreme or 'unnatural' weather resulting from climate change. We also show that the way in which people interpret cold weather is associated with levels of pre-existing scepticism about climate change, which is in turn related to more general worldviews. Drawing attention to 'extreme' weather as a consequence of climate change can be a useful communication device, however this is problematic in the case of seasonal cold.
  • Authors:
    • Merz, K.
    • Stolnikova, E.
    • Wiesenberg, G. L. B.
    • Hafner, S.
    • Kuzyakov, Y.
  • Source: Regular Article
  • Volume: 380
  • Issue: 1-2
  • Year: 2014
  • Summary: This study analyzed the extent to which root exudates diffuse from the root surface towards the soil depending on topsoil and subsoil properties and the effect of arbuscular mycorrhizal fungal hyphae on root-derived C distribution in the rhizosphere. Alfalfa was grown in three-compartment pots. Nylon gauze prevented either roots alone or roots and arbuscular mycorrhizal fungal hyphae from penetrating into the rhizosphere compartments. (CO2)-C-14 pulse labeling enabled the measurement of C-14-labeled exudates in dissolved (DOC) and total organic carbon (TOC) in the rhizosphere, distributed either by diffusion alone or by diffusion, root hair and hyphal transport. Root exudation and microbial decomposition of exudates was higher in the rhizosphere with topsoil compared to subsoil properties. Exudates extended over 28 mm (DOC) and 20 mm (TOC). Different soil properties and mycorrhization, likely caused by the low arbuscular mycorrhizal colonization of roots (13 +/- 4 % (topsoil properties) and 18 +/- 5 % (subsoil properties)), had no effect. Higher microbial decomposition compensated for higher root exudation into the rhizosphere with topsoil properties, which resulted in equal exudate extent when compared to the rhizosphere with subsoil properties. Higher C-14 activity used for labeling compared with previous studies enabled the detection of low exudate concentrations at longer distances from the root surface.
  • Authors:
    • Jurasinski, G.
    • Hoffmann, T.
    • Hoffmann, U.
    • Glatzel, S.
    • Kuhn, N. J.
  • Source: Journal
  • Volume: 232
  • Year: 2014
  • Summary: Mountain environments represent heterogeneous environments with shallow soils that are sensitive to human impact and climate change. Despite the thin soil cover, high soil organic carbon content of mountain soils may provide a major source of atmospheric CO2, if released. However, the importance of mountain soils remains controversial, largely due to insufficient information on the spatial variability of mountain SOC stocks. Here, we study the spatial variability of soil properties and SOC stocks in a changing mountain environment in the Bernese Alps (Switzerland) and the methodologies to assess them. We use different interpolation techniques (averaging, inverse distance, ordinary-, block- and regression-kriging) and sampling densities and analyze the sources of uncertainty using a nested sampling approach and the Gaussian and Taylor error propagation. We found a low sensitivity of the median SOC stocks of the study area (ranging between 8.1 and 8.6 kg C m(-2) in the upper 30 cm), the general patterns of the predicted stocks and the explanatory power with respect to the utilized interpolation techniques. In contrast the small-scale SOC pattern fluctuates strongly between different interpolation techniques. All interpolation techniques, except regression kriging, show a low variability of the calculated root mean square errors of the predicted SOC stocks in terms of variable sampling densities. To improve spatial prediction using regression kriging, which combines the kriging approach with multiple linear regression based on factors controlling the SOC variability (e.g. soil type, land use and topography), large sampling density (>35 samples per km(2)) is required in alpine environments. This is especially true for the coarse mineral fraction, which introduces the largest source of uncertainty. Nested sampling designs seem to provide an efficient tool to study SOC inventories and their associated sources of uncertainties in mountain environments. (C) 2014 Elsevier B.V. All rights reserved.
  • Authors:
    • Gisladottir, G.
    • Zinn, Y. L.
    • Mayes, M. A.
    • Jagadamma, S.
    • Russell, A. E.
  • Source: Article
  • Volume: 213
  • Year: 2014
  • Summary: Dissolved organic carbon (DOC) transported from the soil surface is stabilized in deeper soil profiles by physicochemical sorption processes. However, it is unclear how different forms of organic carbon (OC) compounds common in soil organic matter interact with soil minerals in the surface (A) and subsurface (B) horizons. We added four compounds (glucose, starch, cinnamic acid and stearic acid) to the silt- and clay-sized fraction (fine fraction) of A and B horizons of eight soils from varying climates (3 temperate, 3 tropical, 1 arctic and 1 sub-arctic). Equilibrium batch experiments were conducted using 0 to 100 mg C L-1 of C-14-labeled compounds for 8 h. Sorption parameters (maximum sorption capacity, Q(max) and binding coefficient, k) calculated by fitting sorption data to the Langmuir equation showed that Q(max) of A and B horizons was very similar for all compounds. Both Q(max) and k values were related to sorbate properties, with Q(max) being lowest for glucose (20-500 mg kg(-1)), highest for stearic acid (20,000-200,000 mg kg(-1)), and intermediate for both cinnamic acid (200-4000 mg kg(-1)) and starch (400-6000 mg kg(-1)). Simple linear regression analysis revealed that physicochemical properties of the sorbents influenced the Q(max), of cinnamic acid and stearic acid, but not glucose and starch. The sorbent properties did not show predictive ability for binding coefficient k. By using the fine fraction as sorbent, we found that the mineral fractions of A horizons are equally reactive as the B horizons irrespective of soil organic carbon content. (C) 2013 Elsevier B.V. All rights reserved.
  • Authors:
    • Thiele-Bruhn, S.
    • Ludwig, M.
    • Vohland, M.
    • Ludwig, B.
  • Source: Geoderma
  • Volume: 223
  • Year: 2014
  • Summary: Spectral variable selection is an important step in spectroscopic data analysis, as it tends to parsimonious data representation and can result in multivariate models with greater predictive ability. In this study, we used VIS-NIR (visible to near-infrared) diffuse reflectance and DRIFT (diffuse reflectance infrared Fourier transform in the mid-infrared range, MIR) spectroscopy to determine a series of chemical and biological soil properties. Multivariate calibrations were performed with partial least squares regression (PLSR) using the full absorbance spectra (VIS-NIR: 400-2500 nm with 5-nm intervals; MIR: 4000-800 cm(-1) with 4-cm(-1) intervals) and with a combination of PLSR and CARS (competitive adaptive reweighted sampling) to integrate only the most informative key variables. The CARS procedure has as yet not been applied in the field of soil spectroscopy. As set heterogeneity is crucial for an optimal calibration, we tested these approaches to a sample set of 60 agricultural samples covering a broad range of different parent materials, soil textures, organic matter contents and soil pH values. Soil samples were taken from the Ap horizon (0-10 cm depth), air-dried and pulverised before the lab spectroscopic measurements were performed. In a cross-validation approach, the CARS-PLSR method was markedly more accurate than full spectrum-PLSR for all investigated soil variables and both spectral regions. With MIR data and CARS-PLSR, excellent results (indicated by a residual prediction deviation (RPD) greater than 3.0) were obtained for organic carbon (OC), nitrogen (N), microbial biomass-C (C-mic) and pH values; for hot water extractable C (C-hwe), RPD was 2.60. The accuracies obtained with VIS-NIR data were considerably lower than those with the MIR spectra; best results were retrieved for pH and C-mic (approximately quantitative as indicated by RPD values between 2.0 and 2.5). The information content of the MIR data was substantially different from the VIS-NIR information, as indicated by 2D correlation analysis. We found an overall blurred 2D correlation pattern between both spectral regions with moderate to low correlation coefficients, which suggested that the heterogeneity of the studied soil sample population had led to a very complex blurring of overtones and combination bands in the NIR region. Statistical CARS selections were physically reasonable. MIR key wavenumbers for the studied C fractions were inter alia identified at the bands at 2920 cm(-1) and 2850 cm(-1) (both aliphatic CH-groups) and the region between 1740 and 1600 cm(-1) (CO-groups) and represent hydrophobic and hydrophilic compounds of soil organic matter. Important VIS-NIR wavelengths for assessing C fractions and N were located nearby the prominent water absorption band at 1915 nm and the hydroxyl band at 2200 nm. The simplicity of the approach, parsimony of the multivariate models, accuracy levels in the cross-validation and physically reasonable selections indicated a successful operation of the CARS procedure. It should be further examined with a larger number of samples using separate calibration and validation sets. (C) 2014 Elsevier B.V. All rights reserved.
  • Authors:
    • Siegfried, W.
    • Rohr, C.
    • Riemann, D.
    • Retso, D.
    • Pribyl, K.
    • Nordl, O.
    • Litzenburger, L.
    • Limanowka, D.
    • Labbe, T.
    • Kotyza, O.
    • Kiss, A.
    • Himmelsbach, I.
    • Glaser, R.
    • Dobrovolny, P.
    • Contino, A.
    • Camenisch, C.
    • Burmeister, K.
    • Brazdil, R.
    • Bieber, U.
    • Barriendos, M.
    • Alcoforado, M.
    • Luterbacher, J.
    • Gruenewald, U.
    • Herget, J.
    • Seneviratne, S.
    • Wagner, S.
    • Zorita, E.
    • Werner, J.
    • Pfister, C.
    • Wetter, O.
    • Soderberg, J.
    • Spring, J.
  • Source: Climatic Change
  • Volume: 125
  • Issue: 3-4
  • Year: 2014
  • Summary: The heat waves of 2003 in Western Europe and 2010 in Russia, commonly labelled as rare climatic anomalies outside of previous experience, are often taken as harbingers of more frequent extremes in the global warming-influenced future. However, a recent reconstruction of spring-summer temperatures for WE resulted in the likelihood of significantly higher temperatures in 1540. In order to check the plausibility of this result we investigated the severity of the 1540 drought by putting forward the argument of the known soil desiccation-temperature feedback. Based on more than 300 first-hand documentary weather report sources originating from an area of 2 to 3 million km(2), we show that Europe was affected by an unprecedented 11-month-long Megadrought. The estimated number of precipitation days and precipitation amount for Central and Western Europe in 1540 is significantly lower than the 100-year minima of the instrumental measurement period for spring, summer and autumn. This result is supported by independent documentary evidence about extremely low river flows and Europe-wide wild-, forest- and settlement fires. We found that an event of this severity cannot be simulated by state-of-the-art climate models.
  • Authors:
    • Rappaport, A. G.
    • Mitra, S.
    • Francis, B.
    • Harris, R.
    • Thomson, A. M.
    • Reeves, J. B.
    • Ebinger, M. H.
    • Wielopolski, L.
    • Rice, C. W.
    • Izaurralde, R. C.
    • Etchevers, J. D.
    • Sayre, K. D.
    • Govaerts, B.
    • McCarty, G. W.
  • Source: PLOS ONE
  • Volume: 8
  • Issue: 1
  • Year: 2013
  • Summary: Three advanced technologies to measure soil carbon (C) density (g C m -2) are deployed in the field and the results compared against those obtained by the dry combustion (DC) method. The advanced methods are: (a) Laser Induced Breakdown Spectroscopy (LIBS), (b) Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS), and (c) Inelastic Neutron Scattering (INS). The measurements and soil samples were acquired at Beltsville, MD, USA and at Centro International para el Mejoramiento del Maiz y el Trigo (CIMMYT) at El Batan, Mexico. At Beltsville, soil samples were extracted at three depth intervals (0-5, 5-15, and 15-30 cm) and processed for analysis in the field with the LIBS and DRIFTS instruments. The INS instrument determined soil C density to a depth of 30 cm via scanning and stationary measurements. Subsequently, soil core samples were analyzed in the laboratory for soil bulk density (kg m -3), C concentration (g kg -1) by DC, and results reported as soil C density (kg m -2). Results from each technique were derived independently and contributed to a blind test against results from the reference (DC) method. A similar procedure was employed at CIMMYT in Mexico employing but only with the LIBS and DRIFTS instruments. Following conversion to common units, we found that the LIBS, DRIFTS, and INS results can be compared directly with those obtained by the DC method. The first two methods and the standard DC require soil sampling and need soil bulk density information to convert soil C concentrations to soil C densities while the INS method does not require soil sampling. We conclude that, in comparison with the DC method, the three instruments (a) showed acceptable performances although further work is needed to improve calibration techniques and (b) demonstrated their portability and their capacity to perform under field conditions.
  • Authors:
    • Aubinet, M.
    • Roisin, C.
    • Buysse, P.
  • Source: Agriculture Ecosystems and Enviroment
  • Volume: 167
  • Issue: 52-59
  • Year: 2013
  • Summary: Crop management exerts a strong influence on the soil carbon (C) balance. This study investigated a long-term experiment initiated in 1959 at a site in the Hesbaye region of Belgium and focused on three contrasted treatments: residue export (RE), farmyard manure (FYM) addition and residue restitution (RR) after harvest. The objectives were to quantify the components of the C budget of croplands from a 50-year perspective and to identify the impact of the treatments on this budget and soil C sequestration, given the relatively low levels of residue application. The soil C budget was calculated for each treatment on the basis of total soil organic C (SOC) content measurements and C input data collected since the experiment had begun and drawn from the literature. To evaluate the robustness of this approach, the budget-based output estimates were compared with annual heterotrophic respiration (HR) averages extrapolated from seasonal field HR measurements carried out at the same experimental site in 2010. The soil C budget-based output estimates accorded well with field-based HR measurements and with most HR estimates in the literature, suggesting that, despite the many uncertainties affecting the soil C budget, these results were robust. The three treatments investigated in this study had different impacts on SOC stocks, mainly during the first 20 years of the experiment. RE and FYM caused significant SOC decreases (on average, -75 g C m -2 year -1 over the 50 years) and increases (105 g C m -2 year -1), respectively, whereas RR had no significant impact on the SOC stocks. The study also showed (i) the very large part (about two-thirds of the total input) that represented the below-ground input, weeds and other left-over residues in the C budget, (ii) the important role probably played by residue quality in C sequestration and (iii) the large proportion of C lost annually from the soil (which represents 93-98, 100 and 102-107% of the amounts of fresh residue brought to the soil each year in the FYM, RR and RE treatments, respectively).
  • Authors:
    • Labreuche, J.
    • Cohan, J. P.
    • Dimassi, B.
    • Mary, B.
  • Source: Agriculture Ecosystems and Envirtoment
  • Volume: 169
  • Year: 2013
  • Summary: Although continuous no-till (NT) is recommended for erosion control and carbon sequestration, it often has a limited duration since farmers alternate between NT and full inversion tillage (FIT) to control weed infestation and avoid soil compaction. In this paper, we evaluate the effect of continuous tillage and tillage conversion of NT to FIT and vice versa on SOC and SON stocks, in a long-term experiment at Boigneville in Northern France. Continuous NT (CNT) and FIT (CFIT) treatments were established in 1991 and maintained until 2011 while half of the plots were converted in 2005: from CNT to new FIT (NFIT) and CFIT to new NT (NNT). Bulk densities and organic C and N contents were determined in 2001 and 2011 down to the old ploughing depth ( opd) which was also measured. SOC and SON stocks were calculated at equivalent soil mass by correcting either bulk densities or the opd. Both methods produced very close results and similar conclusions. A typical gradient of SOC and SON concentrations vs depth was observed in CNT as opposed to a rather uniform distribution in CFIT. CNT resulted in SOC concentration in the top soil (0-5 cm) higher by 38% in 2001 and 53% in 2011 compared to CFIT. Conversely, it led to a SOC reduction in the deeper layer ( ca. 10-28 cm) by 14% in 2001 and 18% in 2011. The global effect was no significant change in SOC and SON stocks between treatments over the old ploughed layer (4060 t soil ha -1) in both years: 43.2 and 45.0 t C ha -1 in 2001 and 44.7 and 45.8 t C ha -1 in 2011, in CNT and CFIT, respectively. In 2011, six years after tillage conversion, the stratification of SOC and SON had disappeared in NFIT whereas a new one had appeared in NNT with a smaller gradient than in CNT. SOC or SON stocks over the old ploughed layer did not differ significantly between treatments after 6 years of conversion: SOC stocks were 45.8, 43.2, 44.7 and 43.1 t C ha -1 in the CFIT, NFIT, CNT and NNT treatments, respectively. Furthermore, SOC stocks below the old ploughed layer ( ca. 28-40 cm) were slightly greater in FIT than in NT treatment (10.9 vs 8.7 t C ha -1). In this experiment, continuous or conversion tillage did not result in any C sequestration benefit.
  • Authors:
    • Smith, P.
    • Williams, M.
    • Forristal, D.
    • Lanigan, G.
    • Osborne, B.
    • Abdalla, M.
    • Jones, M. B.
  • Source: Soil Use and Management
  • Volume: 29
  • Issue: 2
  • Year: 2013
  • Summary: Conservation tillage (CT) is an umbrella term encompassing many types of tillage and residue management systems that aim to achieve sustainable and profitable agriculture. Through a global review of CT research, the objective of this paper was to investigate the impacts of CT on greenhouse gas (GHG) emissions. Based on the analysis presented, CT should be developed within the context of specific climates and soils. A number of potential disadvantages in adopting CT practices were identified, relating mainly to enhanced nitrous oxide emissions, together with a number of advantages that would justify its wider adoption. Almost all studies examined showed that the adoption of CT practices reduced carbon dioxide emissions, while also contributing to increases in soil organic carbon and improvements in soil structure.