• Authors:
    • Southway, S.
    • Simper, J.
    • Birkett, T.
    • Moreby, S.
    • Oaten, H.
    • Holland, J. M.
    • Smith, B. M.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 155
  • Year: 2012
  • Summary: The impact of two predatory guilds, epigeal and aerial natural enemies, on levels of cereal aphid control in winter wheat was examined on farms with contrasting proportions of grass margins, one of the most popular agri-environment options in England. In year 1, by 14 d after inoculation the aerial natural enemies alone had caused substantial reductions (88%) in numbers of cereal aphids compared to where no natural enemies were present. In contrast, epigeal predators achieved a 31% reduction, although this reached 88% after 28 d. In year 2, both aerial and epigeal natural enemies achieved over 87% control after 14 d. Aerial natural enemies were largely comprised of predatory Diptera and Linyphiidae (Araneae). Levels of control were positively related to the proportion of linear grass margins within 250, 500 and 750 m radii of the study arenas. There was weaker evidence that hedgerows decreased aphid control by epigeal predators. This study demonstrated that an agri-environment option can be used to improve an ecosystem service on arable farmland.
  • Authors:
    • Sheppard, L. J.
    • Ostle, N.
    • Mills, R.
    • Mcnamara, N. P.
    • Jones, T.
    • Jones, S. K.
    • Gray, A.
    • Gaiawyn, J.
    • Fowler, D.
    • Evans, C.
    • Drewer, J.
    • Dinsmore, K. J.
    • Cooper, M. D. A.
    • Burden, A.
    • Levy, P. E.
    • Skiba, U.
    • Sowerby, A.
    • Ward, S. E.
    • Zielinski, P.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 5
  • Year: 2012
  • Summary: Nearly 5000 chamber measurements of CH 4 flux were collated from 21 sites across the United Kingdom, covering a range of soil and vegetation types, to derive a parsimonious model that explains as much of the variability as possible, with the least input requirements. Mean fluxes ranged from -0.3 to 27.4 nmol CH 4 m -2 s -1, with small emissions or low rates of net uptake in mineral soils (site means of -0.3 to 0.7 nmol m -2 s -1) and much larger emissions from organic soils (site means of -0.3 to 27.4 nmol m -2 s -1). Less than half of the observed variability in instantaneous fluxes could be explained by independent variables measured. The reasons for this include measurement error, stochastic processes and, probably most importantly, poor correspondence between the independent variables measured and the actual variables influencing the processes underlying methane production, transport and oxidation. When temporal variation was accounted for, and the fluxes averaged at larger spatial scales, simple models explained up to ca. 75% of the variance in CH 4 fluxes. Soil carbon, peat depth, soil moisture and pH together provided the best sub-set of explanatory variables. However, where plant species composition data were available, this provided the highest explanatory power. Linear and nonlinear models generally fitted the data equally well, with the exception that soil moisture required a power transformation. To estimate the impact of changes in peatland water table on CH 4 emissions in the United Kingdom, an emission factor of +0.4 g CH 4 m -2 yr -1 per cm increase in water table height was derived from the data.
  • Authors:
    • Goulding, K. W. T.
    • Macdonald, A. J.
    • Coleman, K.
    • Chambers, B. J.
    • Bhogal, A.
    • Powlson, D. S.
    • Whitmore, A. P.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 146
  • Issue: 1
  • Year: 2012
  • Summary: Results from the UK were reviewed to quantify the impact on climate change mitigation of soil organic carbon (SOC) stocks as a result of (1) a change from conventional to less intensive tillage and (2) addition of organic materials including farm manures, digested biosolids, cereal straw, green manure and paper crumble. The average annual increase in SOC deriving from reduced tillage was 310 kg C180 kg C ha -1 yr -1. Even this accumulation of C is unlikely to be achieved in the UK and northwest Europe because farmers practice rotational tillage. N 2O emissions may increase under reduced tillage, counteracting increases in SOC. Addition of biosolids increased SOC (in kg C ha -1 yr -1 t -1 dry solids added) by on average 6020 (farm manures), 18024 (digested biosolids), 5015 (cereal straw), 6010 (green compost) and an estimated 60 (paper crumble). SOC accumulation declines in long-term experiments (>50 yr) with farm manure applications as a new equilibrium is approached. Biosolids are typically already applied to soil, so increases in SOC cannot be regarded as mitigation. Large increases in SOC were deduced for paper crumble (>6 t C ha -1 yr -1) but outweighed by N 2O emissions deriving from additional fertiliser. Compost offers genuine potential for mitigation because application replaces disposal to landfill; it also decreases N 2O emission.
  • Authors:
    • Rousk, J.
    • Gertler, C.
    • Marsden, K. A.
    • Quilliam, R. S.
    • DeLuca, . H.
    • Jones, D. L.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 158
  • Year: 2012
  • Summary: Evidence suggests that in addition to sequestering carbon (C), biochar amendment can increase crop yields, improve soil quality and nutrient cycling, reduce the leaching of nutrients from soil and stimulate soil microbial activity. However, biochar application primarily benefits soils of intrinsic poor quality, thus the advantages of adding biochar to temperate agricultural soils remains controversial. In addition, there is limited information about the longer term effects of biochar application, or of increasing the rate of biochar loading to soil. Therefore, the aim of this study was to determine the effect of biochar residency time and application rate on soil quality, crop performance, weed emergence, microbial growth and community composition in a temperate agricultural soil. We used replicated field plots with three wood biochar application rates (0, 25 and 50 t ha -1). Three years after biochar amendment, the plots were further split and fresh biochar added at two different rates (25 and 50 t ha -1) resulting in double-loaded reapplications of 25+25 and 50+50 t ha -1. After a soil residency time of three years, there were no significant differences in soil nutrients, microbial growth, mycorrhizal colonisation or weed emergence between biochar amended and unamended soil. In contrast, the reapplication of biochar had a significant effect on soil quality, (e.g. increased PO 43-, K + and Ca 2+, DOC, soil moisture, organic matter and EC), microbial growth, (e.g. decreased saprophytic fungal growth), increased mycorrhizal root colonisation and inhibition of weed emergence. Whilst biochar application is unquestionably a strategy for the sequestration of C, in this case, other benefits, e.g. improved soil nutrient levels or crop performance, seemed to be short lived. Reapplication of biochar exemplifies the transient nature of biochar-mediated benefits rather than any lasting differences in soil nutrient dynamics or microbial communities. These results emphasise the need for more long-term field studies to provide data that can meaningfully inform agronomic management decisions and climate change mitigation strategies.
  • Authors:
    • Ball, B. C.
    • Yamulki, S.
    • Chadwick, D. R.
    • Watson, C. J.
    • Thorman, R.
    • Dobbie, K. E.
    • Smith, K. A.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 93
  • Issue: 2
  • Year: 2012
  • Summary: Nitrous oxide emission factors (EFs) were calculated from measurements of emissions from UK wheat crops and grassland, that were part of a wider research programme on N loss pathways and crop responses. Field studies were undertaken in 2003, 2004 and 2005-a total of 12 site-seasons. Nitrous oxide emissions were measured by the closed static chamber method, following the application of various N fertilizer forms (ammonium nitrate (AN), calcium ammonium nitrate (CAN), urea (UR), urea ammonium sulphate and urea ammonium nitrate) at the recommended rates. Emission factors for the growing season (March-September) ranged from less than 0.1-3.9 %. In the 2nd year, measurements continued at three sites until the following February; the resulting annual EFs were one-third greater, on average, than those for the growing season. There was some evidence that N2O emissions from UR were smaller than from AN or CAN, but when this was adjusted for loss of ammonia by volatilization, there was generally little difference between different forms of N. Emissions from UR modified by the addition of the urease inhibitor nBTPT (UR + UI) were lower than corresponding emissions from nitrate forms, except under conditions where emissions were generally low, even allowing for indirect emissions, suggesting that the use of a urease inhibitor can provide some mitigation of N2O, as well as NH3, emissions. The emission data broadly bear out the relationships obtained in earlier UK studies, showing a strong dependence of N2O emission on soil wetness, temperature and the presence of sufficient mineral N in the soil, which decreases rapidly after N application mainly as a result of plant uptake. Overall net mean EFs for the whole season (after subtracting background emissions from unfertilized controls) covered a range wider than the 0.3-3.0 % range of IPCC (2006).
  • Authors:
    • Storkey, J.
    • Stratonovitch, P.
    • Semenov, M. A.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 6
  • Year: 2012
  • Summary: Predicting the impact of climate change on the damage niche of an agricultural weed at a local scale requires a process-based modelling approach that integrates local environmental conditions and the differential responses of the crop and weed to change. A simulation model of the growth and population dynamics of winter wheat and a competing weed, Sirius 2010, was calibrated and validated for the most economically damaging weed in UK cereals, Alopecurus myosuroides. The model was run using local-scale climatic scenarios generated by the LARS-WG weather generator and based on the HadCM3 projections for the periods 2046-2065 and 2080-2099 to predict the impact of climate change on the population dynamics of the weed and its effect on wheat yields. Owing to rising CO 2 concentration and its effect on radiation use efficiency of wheat, weed-free wheat yields were predicted to increase. The distribution of the weed was predicted to remain broadly similar with a possible northward shift in range. Local-scale variation in the impact of climate change was apparent owing to variation in soil type and water holding capacity. The competitive balance was shifted in favour of the deeper rooted crop under climate change, particularly on sites with lighter soils, owing to more frequent and severe drought stress events. Although the damage niche of A. myosuroides was predicted to reduce under climate change, it is likely that weeds with contrasting physiology, such as C4 species, will be better adapted to future conditions and pose a more serious threat.
  • Authors:
    • Matthews, R.
    • Balana, B. B.
    • Bakam, I.
  • Source: Journal of Environmental Management
  • Volume: 112
  • Issue: December
  • Year: 2012
  • Summary: Market-based policy instruments to reduce greenhouse gas (GHG) emissions are generally considered more appropriate than command and control tools. However, the omission of transaction costs from policy evaluations and decision-making processes may result in inefficiency in public resource allocation and sub-optimal policy choices and outcomes. This paper aims to assess the relative cost-effectiveness of market-based GHG mitigation policy instruments in the agricultural sector by incorporating transaction costs. Assuming that farmers' responses to mitigation policies are economically rationale, an individual-based model is developed to study the relative performances of an emission tax, a nitrogen fertilizer tax, and a carbon trading scheme using farm data from the Scottish farm account survey (FAS) and emissions and transaction cost data from literature metadata survey. Model simulations show that none of the three schemes could be considered the most cost effective in all circumstances. The cost effectiveness depends both on the tax rate and the amount of free permits allocated to farmers. However, the emissions trading scheme appears to outperform both other policies in realistic scenarios. (C) 2012 Elsevier Ltd. All rights reserved.
  • Authors:
    • Goicoechea, N.
    • Garmendia, I.
    • Baslam, M.
  • Source: Annals of Applied Biology
  • Volume: 161
  • Issue: 2
  • Year: 2012
  • Summary: Arbuscular mycorrhizal fungi (AMF) can improve growth and nutritional quality of greenhouse-grown lettuces cultivated at ambient CO2. Moreover, mycorrhizal symbiosis is predicted to be important in defining plant responses to elevated atmospheric CO2 concentrations. Our main objective was to assess the effects of elevated CO2 on growth and nutritional quality of greenhouse-grown lettuces inoculated or not with AMF. Results showed that the accumulation of mineral nutrients (e.g. P, Cu, Fe) and antioxidant compounds (carotenoids, phenolics, anthocyanins, ascorbate) induced by AMF in leaves of lettuces cultivated at ambient CO2 may diminish or disappear under elevated CO2. It is hypothesized that a relevant quantity of photoassimilates could be used for improving shoot growth and spreading mycorrhizal colonization in detriment to the secondary metabolism. However, important differences can be found among different cultivars of lettuces.
  • Authors:
    • Fitt, B. D. L.
    • Smith, P.
    • West, J. S.
    • Carlton, R. R.
  • Source: European Journal of Plant Pathology
  • Volume: 133
  • Issue: 1
  • Year: 2012
  • Summary: Crop disease not only threatens global food security by reducing crop production at a time of growing demand, but also contributes to greenhouse gas (GHG) emissions by reducing efficiency of N fertiliser use and farm operations and by driving land use change. GHG emissions associated with adoption of reduced tillage, organic and integrated systems of field crop production across the UK and selected regions are compared with emissions from conventional arable farming to assess their potential for climate change mitigation. The reduced tillage system demonstrated a modest (< 20%) reduction in emissions in all cases, although in practice it may not be suitable for all soils and it is likely to cause problems with control of diseases spread on crop debris. There were substantial increases in GHG emissions associated with the organic and integrated systems at national level, principally due to soil organic carbon losses from land use change. At a regional level the integrated system shows the potential to deliver significant emission reductions. These results indicate that the conventional crop production system, coupled to reduced tillage cultivation where appropriate, is generally the best for producing high yields to minimise greenhouse gas emissions and contribute to global food security, although there may be scope for use of the integrated system on a regional basis. The control of crop disease will continue to have an essential role in both maintaining productivity and decreasing GHG emissions.
  • Authors:
    • Zegada-Lizarazu, W.
    • Walter, K.
    • Valentine, J.
    • Djomo, S. Njakou
    • Monti, A.
    • Mander, U.
    • Lanigan, G. J.
    • Jones, M. B.
    • Hyvonen, N.
    • Freibauer, A.
    • Flessa, H.
    • Drewer, J.
    • Carter, M. S.
    • Skiba, U.
    • Hastings, A.
    • Osborne, B.
    • Don, A.
    • Zenone, T.
  • Source: GCB Bioenergy
  • Volume: 4
  • Issue: 4
  • Year: 2012
  • Summary: Bioenergy from crops is expected to make a considerable contribution to climate change mitigation. However, bioenergy is not necessarily carbon neutral because emissions of CO2, N2O and CH4 during crop production may reduce or completely counterbalance CO2 savings of the substituted fossil fuels. These greenhouse gases (GHGs) need to be included into the carbon footprint calculation of different bioenergy crops under a range of soil conditions and management practices. This review compiles existing knowledge on agronomic and environmental constraints and GHG balances of the major European bioenergy crops, although it focuses on dedicated perennial crops such as Miscanthus and short rotation coppice species. Such second-generation crops account for only 3% of the current European bioenergy production, but field data suggest they emit 40% to >99% less N2O than conventional annual crops. This is a result of lower fertilizer requirements as well as a higher N-use efficiency, due to effective N-recycling. Perennial energy crops have the potential to sequester additional carbon in soil biomass if established on former cropland (0.44 Mg soil C ha(-1) yr(-1) for poplar and willow and 0.66 Mg soil C ha(-1) yr(-1) for Miscanthus). However, there was no positive or even negative effects on the C balance if energy crops are established on former grassland. Increased bioenergy production may also result in direct and indirect land-use changes with potential high C losses when native vegetation is converted to annual crops. Although dedicated perennial energy crops have a high potential to improve the GHG balance of bioenergy production, several agronomic and economic constraints still have to be overcome.