Inventory of ammonia emissions from UK agriculture 2009

The National Ammonia Reduction Strategy Evaluation System (NARSES) model (spreadsheet version) was used to estimate ammonia (NH3) emissions from UK agriculture for the year 2009. Year-specific livestock numbers and fertiliser N use were added for 2009 and revised for previous years. The estimate for 2009 was 231.8 kt NH3, representing a 2.3 kt increase from the previously submitted estimate for 2008. Backward and forward projections using the 2009 model structure gave estimates of 317, 245 and 244 kt NH3 for the years 1990, 2010 and 2020, respectively. This inventory reports emission from livestock agriculture and from nitrogen fertilisers applied to agricultural land. There are a number of other minor sources reported as ‘agriculture’ in the total UK emission inventory, including horses not kept on agricultural holdings, emissions from composting and domestic fertiliser use

Leaching of phthalate acid esters from plastic mulch films and their degradation in response to UV irradiation and contrasting soil conditions

Phthalate acid esters (PAEs) are commonly used plastic additives, not chemically bound to the plastic that migrate into surrounding environments, posing a threat to environmental and human health. Dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) are two common PAEs found in agricultural soils, where degradation is attributed to microbial decomposition. Yet the impact of the plastic matrix on PAE degradation rates is poorly understood. Using 14C-labelled DBP and DEHP we show that migration from the plastic matrix into soil represents a key rate limiting step in their bioavailability and subsequent degradation. Incorporating PAEs into plastic film decreased their degradation in soil, DBP (DEHP) from 79% to 21% (9% to <1%), over four months when compared to direct application of PAEs. Mimicking surface soil conditions, we demonstrated that exposure to ultraviolet radiation accelerated PAE mineralisation twofold. Turnover of PAE was promoted by the addition of biosolids, while the presence of plants and other organic residues failed to promote degradation. We conclude that PAEs persist in soil for longer than previously thought due to physical trapping within the plastic matrix, suggesting PAEs released from plastics over very long time periods lead to increasing levels of contamination

Dissolved Phosphorus Retention in Buffer Strips: Influence of Slope and Soil Type

Phosphorus (P) contributes to eutrophication of surface waters and buffer strips may be implemented to reduce its transfer from agricultural sources to watercourses. This study was conducted to test the hypothesis that soil type and slope influence the retention of dissolved organic P and inorganic orthophosphate in agricultural runoff in 2-m-wide buffer strip soils. A solution, comprised of dissolved orthophosphate and the organic P compounds glucose-1-phosphate, RNA, and inositol hexakisphosphate (1.8 mg L−1 total P) and a chloride tracer, was applied as simulated overland flow to grassland soil blocks (2 m long × 0.5 m wide × 0.35 m deep), containing intact clay or loam soils, at slope angles of 2, 5, and 10°. Phosphorus forms were determined in the surface and subsurface flow from the soil blocks. Slope had no significant effect on the hydrological behavior of the soil blocks or on the retention of any form of P at the water application rate tested. The clay soil retained 60% of the unreactive P and 21% of the reactive P applied. The loam soil retained 74% of the unreactive P applied but was a net source of reactive P (the load increased by 61%). This indicates leaching of native soil P or hydrolysis of organic compounds and complicates our understanding of P retention in buffer strip soils. Our results suggest that a 2-m buffer strip may be more effective for reducing dissolved unreactive P transfers to surface waters than for reducing the eutrophication risk posed by dissolved reactive P

A High Statistics Search for Ultra-High Energy Gamma-Ray Emission from Cygnus X-3 and Hercules X-1

We have carried out a high statistics (2 Billion events) search for ultra-high energy gamma-ray emission from the X-ray binary sources Cygnus X-3 and Hercules X-1. Using data taken with the CASA-MIA detector over a five year period (1990-1995), we find no evidence for steady emission from either source at energies above 115 TeV. The derived upper limits on such emission are more than two orders of magnitude lower than earlier claimed detections. We also find no evidence for neutral particle or gamma-ray emission from either source on time scales of one day and 0.5 hr. For Cygnus X-3, there is no evidence for emission correlated with the 4.8 hr X-ray periodicity or with the occurrence of large radio flares. Unless one postulates that these sources were very active earlier and are now dormant, the limits presented here put into question the earlier results, and highlight the difficulties that possible future experiments will have in detecting gamma-ray signals at ultra-high energies.Comment: 26 LaTeX pages, 16 PostScript figures, uses psfig.sty to be published in Physical Review

Deep-C storage: Biological, chemical and physical strategies to enhance carbon stocks in agricultural subsoils

Due to their substantial volume, subsoils contain more of the total soil carbon (C) pool than topsoils. Much of this C is thousands of years old, suggesting that subsoils offer considerable potential for long-term C sequestration. However, knowledge of subsoil C behaviour and manageability remains incomplete, and subsoil C storage potential has yet to be realised at a large scale, particularly in agricultural systems. A range of biological (e.g. deep-rooting), chemical (e.g. biochar burial) and physical (e.g. deep ploughing) C sequestration strategies have been proposed, but are yet to be assessed. In this review, we identify the main factors that regulate subsoil C cycling and critically evaluate the evidence and mechanistic basis of subsoil strategies designed to promote greater C storage, with particular emphasis on agroecosystems. We assess the barriers and opportunities for the implementation of strategies to enhance subsoil C sequestration and identify 5 key current gaps in scientific understanding. We conclude that subsoils, while highly heterogeneous, are in many cases more suited to long-term C sequestration than topsoils. The proposed strategies may also bring other tangible benefits to cropping systems (e.g. enhanced water holding capacity and nutrient use efficiency). Furthermore, while the subsoil C sequestration strategies we reviewed have large potential, more long-term studies are needed across a diverse range of soils and climates, in conjunction with chronosequence and space-for-time substitutions. Also, it is vital that subsoils are more consistently included in modelled estimations of soil C stocks and C sequestration potential, and that subsoil-explicit C models are developed to specifically reflect subsoil processes. Finally, further mapping of subsoil C is needed in specific regions (e.g. in the Middle East, Eastern Europe, South and Central America, South Asia and Africa). Conducting both immediate and long-term subsoil C studies will fill the knowledge gaps to devise appropriate soil C sequestration strategies and policies to help in the global fight against climate change and decline in soil quality. In conclusion, our evidence-based analysis reveals that subsoils offer an untapped potential to enhance global C storage in terrestrial ecosystems

Consequential life cycle assessment of biogas, biofuel and biomass energy options within an arable crop rotation

Feed in tariffs (FiTs) and renewable heat incentives (RHIs) are driving a rapid expansion in anaerobic digestion (AD) coupled with combined heat and power (CHP) plants in the UK. Farm models were combined with consequential life cycle assessment (CLCA) to assess the net environmental balance of representative biogas, biofuel and biomass scenarios on a large arable farm, capturing crop rotation and digestate nutrient cycling effects. All bioenergy options led to avoided fossil resource depletion. Global warming potential (GWP) balances ranged from -1732kgCO(2)eMg(-1) dry matter (DM) for pig slurry AD feedstock after accounting for avoided slurry storage to +2251kgCO(2)eMg(-1) DM for oilseed rape biodiesel feedstock after attributing indirect land use change (iLUC) to displaced food production. Maize monoculture for AD led to net GWP increases via iLUC, but optimized integration of maize into an arable rotation resulted in negligible food crop displacement and iLUC. However, even under best-case assumptions such as full use of heat output from AD-CHP, crop-biogas achieved low GWP reductions per hectare compared with Miscanthus heating pellets under default estimates of iLUC. Ecosystem services (ES) assessment highlighted soil and water quality risks for maize cultivation. All bioenergy crop options led to net increases in eutrophication after displaced food production was accounted for. The environmental balance of AD is sensitive to design and management factors such as digestate storage and application techniques, which are not well regulated in the UK. Currently, FiT payments are not dependent on compliance with sustainability criteria. We conclude that CLCA and ES effects should be integrated into sustainability criteria for FiTs and RHIs, to direct public money towards resource-efficient renewable energy options that achieve genuine climate protection without degrading soil, air or water qualit

Nutrient (C, N and P) enrichment induces significant changes in the soil metabolite profile and microbial carbon partitioning

The cycling of soil organic matter (SOM) and carbon (C) within the soil is governed by the presence of key macronutrients, particularly nitrogen (N) and phosphorus (P). The relative ratio of these nutrients has a direct effect on the potential rates of microbial growth and nutrient processing in soil and thus is fundamental to ecosystem functioning. However, the effect of changing soil nutrient stoichiometry on the small organic molecule (i.e., metabolite) composition and cycling by the microbial community remains poorly understood. Here, we aimed to disentangle the effect of stoichiometrically balanced nutrient addition on the soil metabolomic profile and apparent microbial carbon use efficiency (CUE) by adding a labile C source (glucose) in combination with N and/or P. After incorporation of the added glucose into the microbial biomass (48 h), metabolite profiling was undertaken by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). 494 metabolites were identified across all treatments mainly consisting of lipids (n = 199), amino acids (n = 118) and carbohydrates (n = 43), >97% of which showed significant changes in concentration between at least one treatment. Overall, glucose-C addition generally increased the synthesis of other carbohydrates in soil, while addition of C and N together increased peptide synthesis, indicative of protein formation and turnover. The combination of C and P significantly increased the number of fatty acids synthesised. There was no significant change in the PLFA-derived microbial community structure or microbial biomass following C, N and P addition. Further, N addition led to an increase in glucose-C partitioning into anabolic processes (i.e., increased CUE), suggesting the microbial community was N, but not P limited. Based on the metabolomic profiles observed here, we conclude that inorganic nutrient enrichment causes substantial shifts in both primary and secondary metabolism within the microbial community, leading to changes in resource flow and thus soil functioning, however, the microbial community illustrated significant metabolic flexibility

Soil pH and phosphorus availability regulate sulphur cycling in an 82-year-old fertilised grassland

The application of lime and mineral fertiliser is known to mitigate soil acidification and improve soil quality in improved grasslands. However, the long-term effect of simultaneous lime and fertiliser amendments on soil carbon (C) and sulphur (S) cycling is still poorly understood. To examine if soil pH or nutrient availability are the dominant factors regulating C and S cycling, we evaluated the biodegradation of methionine (organic S), gross S transformation, and microbial S utilisation using 35S and 14C dual-labelling. Soil samples (0–10 cm) were collected from one unfertilised control and five annual limed (Ca) treatments with or without nitrogen (N), phosphorus (P), potassium (K) and sulphur (S) fertilisers (Ca, CaN, CaNP, CaNPKCl, CaNPK2SO4) in an 82-year-old upland grassland experiment in Rengen, Germany. Long-term lime application increased soil pH values but significantly (p &lt; 0.05) decreased soil organic C content. Fertilisation had no significant effect on microbial utilisation of 35S-labelled methionine, while microbial immobilisation of 35SO42− in the limed soils was significantly reduced compared to the control. This is attributed to either the increased soil pH or decreased C availability after liming. Microbial carbon use efficiency (CUE) was significantly higher in soils with applied P fertiliser (i.e., CaNP: 0.66 ± 0.02, CaNPKCl: 0.68 ± 0.02, CaNPK2SO4: 0.65 ± 0.01) compared to the CaN treatment (0.58 ± 0.01). Moreover, compared to CaN, CaNP and CaNPKCl treatments significantly increased gross S turnover, while no significant effects were observed in the CaNPK2SO4 treatment. Soil P deficits decreased microbial CUE and S bioavailability. Although P fertiliser addition alleviated microbial P limitation when N fertiliser was added, S fertiliser (CaNPK2SO4) present constrained S transformation rates. Overall, the importance of P availability for global S cycling in grasslands is shown, especially under N-enrichment conditions. However, the subsequent potential for C loss from long-term liming should be carefully considered in grassland management