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The effect of clear-fell harvesting on soil greenhouse gas (GHG) fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) was assessed in a Sitka spruce forest growing on a peaty gley organo-mineral soil in northern England. Fluxes from the soil and litter layer were measured monthly by the closed chamber method and gas chromatography over 4 years in two mature stands, with one area harvested after the first year. Concurrent measurements of soil temperature and moisture helped to elucidate reasons for the changes in fluxes. In the 3 years after felling, there was a significant increase in the soil temperature, particularly between June and November (3 to 5 ∘C higher), and in soil moisture, which was 62 % higher in the felled area, and these had pronounced effects on the GHG balance in addition to the removal of the trees and their carbon input to the soil. Annual soil CO2 effluxes reduced to almost a third in the first year after felling (a drop from 24.0 to 8.9 t CO2 ha−1 yr−1) and half in the second and third year (mean 11.8 t CO2 ha−1 yr−1) compared to before felling, while those from the unfelled area were little changed. Annual effluxes of N2O more than doubled in the first two years (from 1.0 to 2.3 and 2.5 t CO2e ha−1 yr−1, respectively), although by the third year they were only 20 % higher (1.2 t CO2e ha−1 yr−1). CH4 fluxes changed from a small net uptake of −0.03 t CO2e ha−1 yr−1 before felling to a small efflux increasing over the 3 years to 0.34 t CO2e ha−1 yr−1, presumably because of the wetter soil after felling. Soil CO2 effluxes dominated the annual net GHG emission when the three gases were compared using their global warming potential (GWP), but N2O contributed up to 20 % of this. This study showed fluxes of CO2, CH4, and N2O responded differently to clear-felling due to the significant changes in soil biotic and abiotic factors and showed large variations between years. This demonstrates the need for multi-year measurements of all GHGs to enable a robust estimate of the effect of the clear-fell phase on the GHG balance of managed forests. This is one of very few multi-year monitoring studies to assess the effect of clear-fell harvesting on soil GHG fluxes.

This paper evaluates the suitability of the ECOSSE model to estimate soil greenhouse gas fluxes from short rotation coppice willow (SRC-Willow), short rotation forestry (SRF-Scots Pine) and Miscanthus after land-use change from conventional systems (grassland and arable). We simulate heterotrophic respiration (Rh), nitrous oxide (N2O) and methane (CH4) fluxes at four paired sites in the UK, and compare them to estimates of Rh derived from the ecosystem respiration estimated from eddy covariance (EC) and Rh estimated from chamber (IRGA) measurements, as well as direct measurements of N2O and CH4 fluxes.Significant association between modelled and EC-derived Rh was found under Miscanthus, with correlation coefficient (r) ranging between 0.54 and 0.70. Association between IRGA-derived Rh and modelled outputs was statistically significant at the Aberystwyth site (r = 0.64) but not significant at the Lincolnshire site (r = 0.29). At all SRC-Willow sites, significant association was found between modelled and measurement-derived Rh (0.44 ? r ? 0.77); significant error was found only for the EC-derived Rh at the Lincolnshire site. Significant association and no significant error were also found for SRF-Scots Pine and perennial grass. For the arable fields, the modelled CO2 correlated well just with the IRGA-derived Rh at one site (r = 0.75). No bias in the model was found at any site, regardless of the measurement type used for the model evaluation.Across all land-uses, fluxes of CH4 and N2O were shown to represent a small proportion of the total greenhouse gas balance; these fluxes have been modelled adequately on a monthly time-step. This study provides confidence in using ECOSSE for predicting the impacts of future land-use on greenhouse gas balance, at site level as well as at national level.

Climate change impacts resulting from fossil fuel combustion and concerns about the diversity of energy supply are driving interest to find low-carbon energy alternatives. As a result bioenergy is receiving widespread scientific, political and media attention for its potential role in both supplying energy and mitigating greenhouse (GHG) emissions. It is estimated that the bioenergy contribution to EU 2020 renewable energy targets could require up to 17-21 million hectares of additional land in Europe (Don et al., 2012). There are increasing concerns that some transitions into bioenergy may not be as sustainable as first thought when GHG emissions from the crop growth and management cycle are factored into any GHG life cycle assessment (LCA). Bioenergy is complex and encapsulates a wide range of crops, varying from food crop based biofuels to dedicated second generation perennial energy crops and forestry products. The decision on the choice of crop for energy production significantly influences the GHG mitigation potential. It is recognised that GHG savings or losses are in part a function of the original land-use that has undergone change and the management intensity for the energy crop. There is therefore an urgent need to better quantify both crop and site-specific effects associated with the production of conventional and dedicated energy crops on the GHG balance. Currently, there is scarcity of GHG balance data with respect to second generation crops meaning that process based models and LCAs of GHG balances are weakly underpinned. Therefore, robust, models based on real data are urgently required. In the UK we have recently embarked on a detailed program of work to address this challenge by combining a large number of field studies with state-of-the-art process models. Through six detailed experiments, we are calculating the annual GHG balances of land use transitions into energy crops across the UK. Further, we are quantifying the total soil carbon gain or loss after land use change at 100 fieldsites which encapsulate a range of UK climates and soil types. Our overall objective is to use our measured data to parameterise and validate the models that we will use to predict the implications of bioenergy crop deployment in the UK up to 2050. The resultant output will be a meta-model which will help facilitate decision making on the sustainable development of bioenergy in the UK, with potential deployment in other temperate climates around the world. Here we report on the outcome of the first of three years of work. This work is based on the Ecosystem Land Use Modelling & Soil Carbon GHG Flux Trial (ELUM) project, which was commissioned and funded by the Energy Technologies Institute (ETI). Don et al. (2012) Land-use change to bioenergy production in Europe: implications for the greenhouse gas balance and soil carbon. GCB Bioenergy 4, 372-379.

Traditionally, dairy cattle spend a substantial part of the year on pastures. For organic farming within EU it is specified that ”all mammals must have access to pasturage or an open-air exercise area” which they must be able to use whenever ”weather conditions and the state of the ground permits” (Council Regulation [EEC] No 2092/91 ). Dairy production systems are characterized by a considerable N surplus, and N deposited during grazing represents a significant risk for environmental losses, including N2O emissions. Excess N is excreted mainly in the urine, the composition of which is influenced by factors such as lactation stage, sward quality and intake of supplements. Resulting N concentrations in urine patches can range from 20 to 80 g N m-2, and soil environmental conditions associated with such a range of N inputs could affect the potential for N2O production via nitrification and denitrification. Soil properties and fertilization also influence N2O emissions. This presentation shows results from a work package within the MIDAIR project which aimed to describe known sources of variability within the grazing system, and their impact on N2O emissions. The objective was to evaluate if management changes can be proposed that will reduce the risk for N2O emissions associated with grazing. Field studies have addressed the heterogeneity of soil physical, chemical and microbiological properties, while plot-scale and laboratory experiments have examined the fate of urinary C and N and the microbial response to urine deposition.

Introduction For Western Europe it is estimated that, on average, 8% of total N excreted by dairy cattle is deposited during grazing (IPCC, 1997). The intake and excretion of N is influenced by factors such as feed composition, lactation stage and pasture quality, and the excretion of excess N as urea in the urine can therefore vary considerably. Urea can lead to high ammonium levels in the soil which may influence N dynamics and gaseous emissions. This laboratory study was conducted to investigate short-term effects of urea concentration on N2O emissions. Methods Solutions containing 0 (CTL), 5 (LU) and 10 g l-1 urea-N (HU) were added to sieved and repacked soil cores of pasture soil at a rate of 4 l m-2. Also, 5 g l-1 urea-N was added to soil amended with 50 μg cm-3 nitrate-N in order to simulate N turnover in overlapping urine spots (LUN). The urea was labelled with 25 atom% 15N. Final soil moisture was 60% WFPS. All treatments were incubated at 14C. Carbon dioxide and N2O evolution rates were determined after c. 0.2, 0.5, 1, 3, 6 and 9 d. At the four last samplings, the replicates used for gas flux measurements were destructively sampled for determination of pH, electrical conductivity (EC), inorganic and total N, as well as dissolved organic C and phospholipid fatty acid composition. On Day 3, soil was also subsampled for determination of potential ammonium oxidation (PAO) and denitrifying enzyme activity (DEA). The amount and isotopic composition of soil N, nitrate, N2O and N2 was determined by IR-MS; labelling of N2 was insignificant. Results and discussion Accumulated CO2 evolution, corrected for CO2 added in urea, was twice as high from HU as from LU, whereas CO2 from LUN was at the level of the CTL treatment after correction. The lower CO2 emission from LUN was associated with a consistent increase in microbial biomass, as reflected in concentrations of PLFA, which suggested that the lower CO2 evolution rate was due to C assimilation rather than growth inhibition. The EC levels in LU, HU and LUN corresponded to osmotic potentials of -0.05 to -0.12 MPa after 1 d, decreasing to between -0.14 and -0.19 MPa after 9 d. These potentials would not normally be stressful, but a negative interaction with high ammonium concentrations has been observed for ammonium oxidation and, particularly, for nitrite oxidation (Harada and Kai, 1968; Stark and Firestone, 1995). PAO measurements after 3d did not indicate any detrimental effects on ammonium oxidisers. Total recovery of urea-N during the experiment was 801.5% (meanS.E.). Soil nitrate accumulated exponentially to concentrations of 90, 60 and 100 mg N kg-1 in LU, HU and LUN after 9 d. Of this, 47, 40 and 58 mg N kg-1 were derived from urea. Nitrification was thus delayed in the HU treatment. Here, a dramatic increase in nitrite concentration to 8 mg N kg-1 was observed between 6 and 9 d, suggesting a selective inhibition of nitrite oxidation. The fact that 33-52% of the nitrate produced was derived from soil N, points to a significant initial turnover of the ammonium pool. Total concentrations of ammonium after 1 d corresponded to 51-61% of urea-N added, and after 3 d to 80-85%. The transient disappearance could be due to microbial assimilation in response to the sudden decrease in osmotic potential. After 6 and 9 d, soil inorganic N corresponded to approximately 100% in LU and LUN, and to 90% in HU. Emissions of N2O during 0-9 d decreased in the order LU>HU>LUN>>CTL and corresponded to 0.1-0.2% of urea-N added. Emission rates for N2O derived from soil were relatively constant in LU, HU and LUN. In HU, the emission of N2O derived from urea increased dramatically between day 6 and 9, parallel to the accumulation of nitrite. Apparently the higher ammonium concentration resulted in accumulation of nitrite which, in turn, led to an accelerated loss of N2O via ammonium oxidation. This implies that management practices which reduce excess N in cattle urine may substantially reduce N2O emissions from grazed pastures.