• Authors:
    • Vogel, A.
    • Strecker, T.
    • Steinauer, K.
    • Richter, A.
    • Ramirez, N.
    • Pierce, S.
    • Rong, J.
    • HongYan, G.
    • FuXun, A.
    • Tilman, D.
    • Scheu, S.
    • Reich, P.
    • Power, S.
    • Roscher, C.
    • Niklaus, P.
    • Manning, P.
    • Milcu, A.
    • Thakur, M.
    • Eisenhauer, N.
  • Source: Global Change Biology
  • Volume: 21
  • Issue: 11
  • Year: 2015
  • Summary: Soil microbial biomass is a key determinant of carbon dynamics in the soil. Several studies have shown that soil microbial biomass significantly increases with plant species diversity, but it remains unclear whether plant species diversity can also stabilize soil microbial biomass in a changing environment. This question is particularly relevant as many global environmental change (GEC) factors, such as drought and nutrient enrichment, have been shown to reduce soil microbial biomass. Experiments with orthogonal manipulations of plant diversity and GEC factors can provide insights whether plant diversity can attenuate such detrimental effects on soil microbial biomass. Here, we present the analysis of 12 different studies with 14 unique orthogonal plant diversity * GEC manipulations in grasslands, where plant diversity and at least one GEC factor (elevated CO 2, nutrient enrichment, drought, earthworm presence, or warming) were manipulated. Our results show that higher plant diversity significantly enhances soil microbial biomass with the strongest effects in long-term field experiments. In contrast, GEC factors had inconsistent effects with only drought having a significant negative effect. Importantly, we report consistent non-significant effects for all 14 interactions between plant diversity and GEC factors, which indicates a limited potential of plant diversity to attenuate the effects of GEC factors on soil microbial biomass. We highlight that plant diversity is a major determinant of soil microbial biomass in experimental grasslands that can influence soil carbon dynamics irrespective of GEC.
  • Authors:
    • Balshaw, H.
    • Williams, J. R.
    • Whitmore, A. P.
    • Ashton, R. W.
    • Webster, C.
    • Scott, T.
    • Cardenas, L.
    • Rees, R. M.
    • Topp, C. F. E.
    • Cloy, J. M.
    • Hinton, N.
    • Bell, M. J.
    • Paine, F.
    • Goulding, K. W. T.
    • Chadwick, D. R.
  • Source: Article
  • Volume: 212
  • Year: 2015
  • Summary: Cultivated agricultural soils are the largest anthropogenic source of nitrous oxide (N 2O), a greenhouse gas approx. 298 times stronger than carbon dioxide. As agricultural land covers 40-50% of the earth's surface agricultural N 2O emissions could significantly influence future climate. The timing, amount and form of manufactured nitrogen (N) fertiliser applied to soils are major controls on N 2O emission magnitude, and various methods are being investigated to quantify and reduce these emissions. A lack of measured N 2O emission factors (EFs) means that most countries report N 2O emissions using the IPCC's Tier 1 methodology, where an EF of 1% is applied to mineral soils, regardless of soil type, climate, or location. The aim of this research was to generate evidence from experiments to contribute to improving the UK's N 2O agricultural inventory, by determining whether N 2O EFs should vary across soil types and agroclimatic zones. Mitigation methods were also investigated, including assessing the impact of the nitrification inhibitor (NI) dicyandiamide (DCD), the application of more frequent smaller doses of fertiliser, and the impact of different rates and forms of manufactured N fertiliser. Nitrous oxide emissions were measured at one cropland site in Scotland and two in England for 12 months in 2011/2012, along with soil and environmental variables. Crop yield was also measured, and emission intensities were calculated for the contrasting fertiliser treatments. The greatest mean annual cumulative emissions from a range of ammonium nitrate (AN) fertiliser rates were measured at the Scottish site (2301 g N 2O-N ha -1), which experienced 822 mm rainfall compared to 418 mm and 472 mm at the English sites, where cumulative annual emissions were lower (929 and 1152 g N 2O-N ha -1, respectively). Climate and soil mineral N influenced N 2O emissions, with a combination of factors required to occur simultaneously to generate the greatest fluxes. Emissions were related to fertiliser N rate; however the trend was not linear. EFs for AN treatments varied between sites, but at both English sites were much lower than the 1% value used by the IPCC, and as low as 0.20%. DCD reduced AN- and urea-generated N 2O emissions and yield-scaled emissions at all sites. AN application in more frequent smaller doses reduced emissions at all sites, however, the type of fertiliser (AN or urea) had no impact. A significant difference in mean annual cumulative emissions between sites reflected differences in rainfall, and suggests that location specific or rainfall driven emission estimates could be considered.
  • Authors:
    • Whitaker, J.
    • Reay, D. S.
    • McNamara, N. P.
    • Case, S. D. C.
  • Source: GCB Bioenergy
  • Volume: 6
  • Issue: 1
  • Year: 2014
  • Summary: Energy production from bioenergy crops may significantly reduce greenhouse gas (GHG) emissions through substitution of fossil fuels. Biochar amendment to soil may further decrease the net climate forcing of bioenergy crop production, however, this has not yet been assessed under field conditions. Significant suppression of soil nitrous oxide (N2O) and carbon dioxide (CO2) emissions following biochar amendment has been demonstrated in short-term laboratory incubations by a number of authors, yet evidence from long-term field trials has been contradictory. This study investigated whether biochar amendment could suppress soil GHG emissions under field and controlled conditions in a MiscanthusxGiganteus crop and whether suppression would be sustained during the first 2years following amendment. In the field, biochar amendment suppressed soil CO2 emissions by 33% and annual net soil CO2 equivalent (eq.) emissions (CO2, N2O and methane, CH4) by 37% over 2years. In the laboratory, under controlled temperature and equalised gravimetric water content, biochar amendment suppressed soil CO2 emissions by 53% and net soil CO2 eq. emissions by 55%. Soil N2O emissions were not significantly suppressed with biochar amendment, although they were generally low. Soil CH4 fluxes were below minimum detectable limits in both experiments. These findings demonstrate that biochar amendment has the potential to suppress net soil CO2 eq. emissions in bioenergy crop systems for up to 2years after addition, primarily through reduced CO2 emissions. Suppression of soil CO2 emissions may be due to a combined effect of reduced enzymatic activity, the increased carbon-use efficiency from the co-location of soil microbes, soil organic matter and nutrients and the precipitation of CO2 onto the biochar surface. We conclude that hardwood biochar has the potential to improve the GHG balance of bioenergy crops through reductions in net soil CO2 eq. emissions.
  • Authors:
    • Wynn, S. C.
    • Kindred, D. R.
    • Sylvester-Bradley, R.
    • Thorman, R. E.
    • Smith, K. E.
  • Source: The Journal of Agricultural Science
  • Volume: 152
  • Issue: 1
  • Year: 2014
  • Summary: Fertilizer nitrogen (N) accounts for the majority of the greenhouse gas (GHG) emissions associated with intensive wheat production, and the form of fertilizer N affects these emissions. Differences in manufacturing emissions (as represented in the current carbon accounting methodologies) tend to favour urea, even when using the best available manufacturing technologies (BAT), whereas differences in fertilizer N efficiency and emissions of ammonia tend to favour ammonium nitrate (AN). To resolve these differences, data from 47 experiments in two large UK studies conducted from 1982 to 1987 and from 2003 to 2005 were reanalysed, showing that on average urea efficiency was 0 center dot 9 of AN (although mean ammonia emissions in 10 subsidiary experiments indicated an efficiency difference of 0 center dot 2); treating urea with a urease inhibitor (TU; AGROTAIN((R)), active ingredient N-(n-butyl) thiophosphoric triamide (n-BTPT)) brought its efficiency almost in line with AN; however, a significantly greater mean optimum N amount for TU (+0 center dot 1 of AN) was not fully explained. A standard response function relating wheat yield to applied AN was modified for degrees of relative inefficiency, thus enabling yields and GHG intensities (kg CO(2)e/tonne (t) grain) to be calculated using a PAS2050 compatible model for GHG emissions for any N amount of any N form. With AN manufactured by average European technology (AET), the estimated GHG intensity of wheat producing 8 t/ha was 451 kg/t; whereas with urea or TU made by AET it was 0.87-0.99 or 0.84-0.86 of this respectively. Using BAT for fertilizer manufacture, the grain's GHG intensity with AN and TU was 368kg/t, but was 1 center dot 03-1 center dot 17 of this with untreated urea. The range of effects on GHG intensities arose mainly from remaining uncertainties in the inefficiencies of the N forms. Generally, economic margins and GHG intensities were not much affected by adjustments in N use for relative inefficiencies or different prices of urea-based fertilizers compared with AN. Overall, TU appeared to provide the best combination of economic performance and GHG intensity, unless the price for N as TU exceeded that for N as AN.
  • Authors:
    • Nevison, I. M.
    • McKenzie, B. M.
    • Hallett, P. D.
    • Gordon, H.
    • Watson, C. A.
    • Rees, R. M.
    • Walker, R. L.
    • Wheatley, R.
    • Topp, C. F. E.
    • Griffiths, B. S.
    • Ball, B. C.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 189
  • Issue: May
  • Year: 2014
  • Summary: Soil management practices shown to increase carbon sequestration include reduced tillage, amendments of carbon and mixed rotations. As a means to mitigate greenhouse gases, however, the success of these practices will be strongly influenced by nitrous oxide (N2O) emissions that vary with soil wetness. Few seasonal data are available on N2O under different soil managements so we measured seasonal N2O emission in three field experiments between 2006 and 2009 in eastern Scotland. The experimental treatments at the three sites were (1) tillage: no-tillage, minimum tillage, ploughing to 20 cm with or without compaction and deep ploughing to 40 cm, (2) organic residue amendment: application of municipal green-waste compost or cattle slurry and (3) rotations: stocked and stockless (without manure) organic arable farming rotations. Most seasons were wetter than average with 2009 the wettest, receiving 20-40% more rainfall than average. Nitrous oxide emissions were measured using static closed chambers. There was no statistical evidence, albeit with low statistical power, that reduced tillage affected N2O emissions compared to normal depth ploughing. With organic residue amendments, only in the wet season in 2008 were emissions significantly increased by high rates of green-waste compost (4.5 kg N2O-N ha(-1)) and cattle slurry (5.2 kg N2O-N ha(-1)) compared to the control (1.9 kg N2O-N ha(-1)). In the organic rotations, N2O emissions were greatest after incorporation of the grass/clover treatments, especially during conversion of a stocked rotation to stockless. Emissions from the organic arable crops (1.9 kg N2O-N ha(-1) in 2006, 3.0 kg N2O-N ha(-1) in 2007) generally exceeded those from the organic grass/clover (0.8 kg N2O-N ha(-1) in 2006, 1.1 kg N2O-N ha(-1) in 2007) except in 2008 when the Wet weather delayed manure applications and increased emissions from the grass/clover (2.8 kg N2O-N ha(-1)). Nevertheless, organic grassland was the land use providing the most effective overall mitigation. Although the magnitude of fluxes did not relate particularly well to rainfall differences between seasons, greater rainfall received during some growing seasons increased the differences between tillage, organic residue and crop rotation phase treatments, negating any possible mitigation by timing management operations in dry periods. This was partly attributed to applying tillage and manures late and/or in wet conditions. Of benefit would be different sampling strategies including closed chambers or eddy covariance with standardised methodology. Controlled soil management experiments with a wide geographic spread to specify land management for mitigation also important. (C) 2014 Elsevier B.V. All rights reserved.
  • Authors:
    • Clay, G. D.
    • Worrall, F.
  • Source: Biomass and Bioenergy
  • Volume: 64
  • Issue: May
  • Year: 2014
  • Summary: Calluna vulgaris can and does grow in areas considered unsuitable for production of biomass crops. In the UK, Calluna vegetation is regularly controlled by burn management and if instead the lost biomass could be harvested would it represent a viable energy crop? This study used established techniques for other energy crops to assess the energy yield, energy efficiency and the greenhouse gas savings represented by cropping of Calluna under two scenarios; only harvested on the area currently under burn management; and harvested on the present total area of Calluna in the UK. The study can consider biomass potential across the UK and can include altitude changes. The study can show that Calluna would represent an efficient energy crop in areas where it would not be possible to revert to functioning peat bogs. The energy efficiency was 65 +/- 19 GJ(output) GJ(input)(-1) with GHG savings of up to 11 tonnes CO2eq, ha(-1) yr(-1). When considered across the UK the potential energy production was up to 40.7 PJ yr(-1) and the potential greenhouse gas saving was upto -2061 ktonnes CO2eq yr(-1) if the all Calluna could be brought into production and substituted for coal. (c) 2014 Elsevier Ltd. All rights reserved.
  • Authors:
    • Hastings, A.
    • Robson, P.
    • Clifton-Brown, J.
    • Zatta, A.
    • Monti, A.
  • Source: GCB Bioenergy
  • Volume: 6
  • Issue: 4
  • Year: 2014
  • Summary: To date, most Miscanthus trials and commercial fields have been planted on arable land. Energy crops will need to be grown more on lower grade lands unsuitable for arable crops. Grasslands represent a major land resource for energy crops. In grasslands, where soil organic carbon (SOC) levels can be high, there have been concerns that the carbon mitigation benefits of bioenergy from Miscanthus could be offset by losses in SOC associated with land use change. At a site in Wales (UK), we quantified the relatively short-term impacts (6 years) of four novel Miscanthus hybrids and Miscanthus x giganteus on SOC in improved grassland. After 6 years, using stable carbon isotope ratios (C-13/C-12), the amount of Miscanthus derived C (C4) in total SOC was considerable (ca. 12%) and positively correlated to belowground biomass of different hybrids. Nevertheless, significant changes in SOC stocks (0-30 cm) were not detected as C4 Miscanthus carbon replaced the initial C3 grassland carbon; however, initial SOC decreased more in the presence of higher belowground biomass. We ascribed this apparently contradictory result to the rhizosphere priming effect triggered by easily available C sources. Observed changes in SOC partitioning were modelled using the RothC soil carbon turnover model and projected for 20 years showing that there is no significant change in SOC throughout the anticipated life of a Miscanthus crop. We interpret our observations to mean that the new labile C from Miscanthus has replaced the labile C from the grassland and, therefore, planting Miscanthus causes an insignificant change in soil organic carbon. The overall C mitigation benefit is therefore not decreased by depletion of soil C and is due to substitution of fossil fuel by the aboveground biomass, in this instance 73-108 Mg C ha(-1) for the lowest and highest yielding hybrids, respectively, after 6 years.
  • Authors:
    • Rounsevell, M. D. A.
    • Moran, D.
    • Alexander, P.
    • Hillier, J.
    • Smith, P.
  • Source: Global Change Biology
  • Volume: 6
  • Issue: 2
  • Year: 2014
  • Summary: Biomass produced from perennial energy crops is expected to contribute to UK renewable energy targets, reducing the carbon intensity of energy production. The UK government has had incentive policies in place targeting both farmers and power plant investors to develop this market, but growth has been slower than anticipated. Market expansion requires the interaction of farmers growing these crops, with the construction of biomass power plants or other facilities to consume them. This study uses an agent-based model to investigate behaviour of the UK energy crop market and examines the cost of emission abatement that the market might provide. The model is run for various policy scenarios attempting to answer the following questions: Do existing policies for perennial energy crops provide a cost-effective mechanism in stimulating the market to achieve emissions abatement? What are the relative benefits of providing incentives to farmers or energy producers? What are the trade-offs between increased or decreased subsidy levels and the rate and level of market uptake, and hence carbon abatement? The results suggest that maintaining the energy crop scheme, which provides farmers' establishment grants, can increase both the emissions abatement potential and cost-effectiveness. A minimum carbon equivalent abatement cost is seen at intermediate subsidy levels for energy generation. This suggests that there is an optimum level that cost-effectively stimulates the market to achieve emissions reduction.
  • Authors:
    • Gundersen, P.
    • Stefansdottir, H. M.
    • Vesterdal, L.
    • Kiar, L. P.
    • Barcena, T. G.
    • Sigurdsson, B. D.
  • Source: Global Change Biology
  • Volume: 20
  • Issue: 8
  • Year: 2014
  • Summary: Northern Europe supports large soil organic carbon (SOC) pools and has been subjected to high frequency of land-use changes during the past decades. However, this region has not been well represented in previous large-scale syntheses of land-use change effects on SOC, especially regarding effects of afforestation. Therefore, we conducted a meta-analysis of SOC stock change following afforestation in Northern Europe. Response ratios were calculated for forest floors and mineral soils (0-10 cm and 0-20/30 cm layers) based on paired control (former land use) and afforested plots. We analyzed the influence of forest age, former land-use, forest type, and soil textural class. Three major improvements were incorporated in the meta-analysis: analysis of major interaction groups, evaluation of the influence of nonindependence between samples according to study design, and mass correction. Former land use was a major factor contributing to changes in SOC after afforestation. In former croplands, SOC change differed between soil layers and was significantly positive (20%) in the 0-10 cm layer. Afforestation of former grasslands had a small negative (nonsignificant) effect indicating limited SOC change following this land-use change within the region. Forest floors enhanced the positive effects of afforestation on SOC, especially with conifers. Meta-estimates calculated for the periods 30 years since afforestation revealed a shift from initial loss to later gain of SOC. The interaction group analysis indicated that meta-estimates in former land-use, forest type, and soil textural class alone were either offset or enhanced when confounding effects among variable classes were considered. Furthermore, effect sizes were slightly overestimated if sample dependence was not accounted for and if no mass correction was performed. We conclude that significant SOC sequestration in Northern Europe occurs after afforestation of croplands and not grasslands, and changes are small within a 30-year perspective.
  • Authors:
    • Poskitt, J.
    • McNamara, N. P.
    • Briones, M. J. I.
    • Crow, S. E.
    • Ostle, N. J.
  • Source: Global Change Biology
  • Volume: 20
  • Issue: 9
  • Year: 2014
  • Summary: Partially decomposed plant and animal remains have been accumulating in organic soils (i.e. >40% C content) for millennia, making them the largest terrestrial carbon store. There is growing concern that, in a warming world, soil biotic processing will accelerate and release greenhouse gases that further exacerbate climate change. However, the magnitude of this response remains uncertain as the constraints are abiotic, biotic and interactive. Here, we examined the influence of resource quality and biological activity on the temperature sensitivity of soil respiration under different soil moisture regimes. Organic soils were sampled from 13 boreal and peatland ecosystems located in the United Kingdom, Ireland, Spain, Finland and Sweden, representing a natural resource quality range of C, N and P. They were incubated at four temperatures (4, 10, 15 and 20°C) at either 60% or 100% water holding capacity (WHC). Our results showed that chemical and biological properties play an important role in determining soil respiration responses to temperature and moisture changes. High soil C : P and C : N ratios were symptomatic of slow C turnover and long-term C accumulation. In boreal soils, low bacterial to fungal ratios were related to greater temperature sensitivity of respiration, which was amplified in drier conditions. This contrasted with peatland soils which were dominated by bacterial communities and enchytraeid grazing, resulting in a more rapid C turnover under warmer and wetter conditions. The unexpected acceleration of C mineralization under high moisture contents was possibly linked to the primarily role of fermented organic matter, instead of oxygen, in mediating microbial decomposition. We conclude that to improve C model simulations of soil respiration, a better resolution of the interactions occurring between climate, resource quality and the decomposer community will be required.