Browsing by Author "Kirk, Guy"
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Item Open Access The biogeochemical origins and plant-availability of potentially toxic elements in sediment from the Thames Estuary(Cranfield University, 2005-08) Shand, Ishbel; Kirk, GuyIn this thesis I investigate the biogeochemical origins and plant availability of potentially toxic elements (PTEs) in sediments dredged from the Thames Estuary. The sediments were pumped from the Thames into silt lagoons on the Rainham Marshes between 1961 and the late 1970s. They are fine-textured and rich in organic matter. The results show that PTE concentrations in the sediments are strongly positively correlated with nitrogen concentrations, and are highly inter-correlated. It is known that this distribution pattern is restricted to ancient and modern sediments from near coastal environments, and hence a link with estuarine processes is suggested. Subsequent investigation showed that the dredgings came from the Thames maximum turbidity zone, and that the lagoons represent a chronological record of changes in sediment quality during a period when dissolved oxygen in the water column rapidly increased. Analysis of one 5 m core from a lagoon showed that there were concurrent substantial changes in the relative proportions of clay, silt and sand in the sediment A novel mechanism is proposed, whereby the textural changes and PTE/organic matter correlation result from mineral dissolution and re-precipitation within flocs in the water column of the maximum turbidity zone. This is mediated by microbial consortia, and is driven by the requirement for Fe(III) as a terminal electron acceptor by dissimilatory iron-reducing bacteria. Potentially toxic elements released from mineral carrier phases are subsequently complexed by various components of the organic fraction or incorporated into secondary minerals and evenly distributed throughout the sediment by tidal action. Published data from historical, geological, hydrological and microbiological science are presented in support of this hypothesis. Foliar concentrations of PTEs in plants grown in the sediments were lower than those predicted by current models, probably because of strong sorption of these elements on sediment solids.Item Open Access Biotic and Abiotic Controls on Calcium Carbonate Formation in Soils(Cranfield University, 2010) Versteegen, Audrey; Milodowski, Antoni; Kirk, Guy; Ritz, K.Over half of the carbon (C) taking part in the global C cycle is held in terrestrial systems. Because of the sensitivity of the C cycle to changes in such soil-based pools of carbon, it is important to understand the basic mechanisms by which soil C is stored and cycled between the range of di erent pools which occur belowground. In the context of climate change mitigation, it is considered that increasing soil-based stocks of C, either by reducing losses from soils, or by actively sequestering new carbon, is a potentially important strategy . Organic carbon is the main form of carbon in soil and as such has received most focus. Cont/d.Item Open Access Effects of hotter, drier conditions on gaseous losses from nitrogen fertilisers(Elsevier, 2023-07-26) Drame, Marieme; Carswell, Alison; Roberts, William; Hood, Jess; Jemo, Martin; Heuer, Sigrid; Kirk, Guy; Pawlett, Mark; Misselbrook, TomGlobal warming is expected to cause hotter, drier summers and more extreme weather events including heat waves and droughts. A little understood aspect of this is its effects on the efficacy of fertilisers and related nutrient losses into the environment. We explored the effects of high soil temperature (>25 °C) and low soil moisture (<40% water filled pore space; WFPS) on emissions of ammonia (NH3) and nitrous oxide (N2O) following application of urea to soil and the efficacy of urease inhibitors (UI) in slowing N losses. We incubated soil columns at three temperatures (15, 25, 35 °C) and three soil moisture contents (20, 40, 60% WFPS) with urea applied on the soil surface with and without UIs, and measured NH3 and N2O emissions using chambers placed over the columns. Four fertiliser treatments were applied in triplicate in a randomised complete block design: (1) urea; (2) urea with a single UI (N-(n-butyl) thiophosphoric triamide (NBPT); (3) urea with two UI (NBPT and N-(n-propyl) thiophosphoric triamide; NPPT); and (4) a zero N control. Inclusion of UI with urea, relative to urea alone, delayed and reduced peak NH3 emissions. However, the efficacy of UI was reduced with increasing temperature and decreasing soil moisture. Cumulative NH3 emission did not differ between the two UI treatments for a given set of conditions and was reduced by 22–87% compared with urea alone. Maximum cumulative NH3 emission occurred at 35 °C and 20% WFPS, accounting for 31% of the applied N for the urea treatment and 25%, on average for the UI treatments. Urease inhibitors did not influence N2O emissions; however, there were interactive impacts of temperature and moisture, with higher cumulative emissions at 40% WFPS and 15 and 25 °C accounting for 1.85–2.62% of the applied N, whereas at 35 °C there was greater N2O emission at 60% WFPS. Our results suggest that inclusion of UI with urea effectively reduces NH3 losses at temperatures reaching 35 °C, although overall effectiveness decreases with increasing temperature, particularly under low soil moisture conditions.Item Open Access Effects of rhizosphere priming and microbial functions on soil carbon turnover(Cranfield University, 2015-04) Lloyd, Davidson A.; Kirk, Guy; Ritz, K.A major uncertainty in soil carbon studies is how inputs of fresh plant-derived carbon affect the turnover of existing soil organic matter (SOM) by so-called priming effects. Priming may occur directly as a result of nutrient mining by existing microbial communities, or indirectly via microbial population adjustments. Soil type and conditions may also influence the intensity and direction of priming effects. However the mechanisms are poorly understood. The objectives of this study were (1) to investigate how additions of labile C4 substrate affected SOM turnover in two contrasting unplanted C3 soils (clayey fertile from Temple Balsall, Warwickshire (TB) and sandy acid from Shuttleworth, Bedfordshire (SH) using13 C isotope shifts; (2) to investigate the influence of rhizodeposition from plant roots on SOM turnover in the same two soils planted with a C4 grass; (3) to assess an automated field system for measuring soil temperature, moisture and photosynthesis sensitivities of SOM turnover in the same two soils over diurnal to seasonal time scales. I used a combination of laboratory incubation, glasshouse and field experiments. In the soil incubation experiment, I made daily applications of either a maize root extract or sucrose to soil microcosms at rates simulating grassland rhizodeposition, and followed soil respiration (Rs) and its δ13 C over 19 days. I inferred the extent of priming from the δ13 C of Rs and the δ13 C of substrate and soil end-members. There were positive priming effects in both soils in response to the two substrates. In the SH soil there were no differences in priming effects between the substrates. However in the TB soil, sucrose produced greater priming effects than maize root extract, and priming effects with sucrose increased over time whereas with maize root extract declined after the first week. I explain these effects in terms of the greater fertility of the TB soil and resulting greater microbial nitrogen mineralization induced by priming. Because the maize root extract contained some nitrogen, over time microbial nitrogen requirements were satisfied without priming whereas with sucrose the nitrogen demand increased over time. In the glasshouse experiment, I planted C4 Kikuyu grass (Pennisetum clandestinum) in pots with the same two soils. The extent of rhizodeposition by the plants was altered by intermittently clipping the grass in half the pots (there were also unplanted controls) and priming effects were inferred from the δ13 C of Rs and the δ13 C of plant and soil end-members. Unclipped plants in both soils generated positive priming effects, while clipping reduced priming in TB soil and produced negligible PEs in SH soil. Microbial nutrient mining of SOM again explained the observed PEs in this experiment. Photosynthesis was a major driver of priming effects in the planted systems. In the third experiment, I found that the tested automated chamber system provided reliable measurements of Rs and net ecosystem exchange (NEE), and it was possible to draw relations for the dependency of Rs and NEE on key environmental drivers. Collectively, the results contribute to a better understanding of the mechanisms of priming effects and highlight possibilities for further research. The methods developed here will allow high temporal and spatial resolution measurements of Rs and NEE under field conditions, using stable isotope methods to separate fluxes into plant- and soil-derived components. Keywords: Soil respiration, soil moisture, soil temperature, Isotope ratio, maize root, flux chamber, climate change, organic matter, rhizodeposition.Item Open Access Full chain analysis of nitrogen use efficiency in rice-livestock systems in Uruguay: identifying opportunities for optimizing N management.(Cranfield University, 2022-11) Castillo Velazquez, Jesus; Kirk, Guy; Haefele, Stephan M.Traditionally the rice crop in Uruguay rotates with pastures for direct livestock grazing. This rotation has allowed a constant rice yield increase of 90 kg ha⁻¹ yr⁻¹ over the past 50 years, with yields averaging 8.4 Mg ha⁻¹ in the last decade. Relatively little nitrogen (N) fertilizer is added (80 kg ha⁻¹ yr⁻¹) and the system shows no sign of soil degradation. By contrast, the livestock component is conducted extensively with mostly (75-80%) unimproved pastures, with low animal productivity (100 kg liveweight ha⁻¹ yr⁻¹). This thesis is concerned with how the system N balance is sustained at regional and national scales and if it can be maintained in the future. The objectives were to quantify the N balance (all N inputs – outputs), N surplus (all N inputs – N removed in food products) and N use efficiency (NUE = N in food products / all N inputs) of different rice-livestock- pasture rotations across Uruguay over time. Because historical records of N inputs and outputs are available at regional and national scales, it was possible to assess the whole system in the long term at a farm-gate level. The DNDC model was parameterised with data from a rice long-term experiment and used to compliment the regional N balance data. Results showed a very high average NUE (55–60%) with N balances around neutrality (-6 to +5 kg N ha⁻¹ yr⁻¹) and low N surplus (20 kg N ha⁻¹ yr⁻¹). These values were worse where pastures have been replaced by other cash-crops or rotations shortened. However, there is an opportunity to intensify the system, maintaining the good N balance by improving the livestock component with improved pastures and higher stocking rates to improve N cycling. Results showed the rice-livestock system of Uruguay is a model mixed farming system with several decades of integration.Item Open Access Geochemical and microbiological controls on the transport of Uranium through soil(Cranfield University, 2009) Stone, Dorothy Grace; Kirk, Guy; Ritz, K.; Harris, Jim A.Widespread use of depleted uranium (DU) in munitions around the world has raised questions about contamination of soils, water and vegetation with uranium (U). However, understanding of processes controlling the fate and behaviour of U in soils is poor. The aim of this research was to investigate the contributions of abiotic and biotic processes to U transport in soils, by measuring transport in well-controlled experimental systems, and comparing the results with predictions of models of solute transport and reaction. Investigating the role of abiotic processes is challenging due to the complex speciation chemistry of U in soil solutions, sorption reactions with soil surfaces, and the kinetics of local equilibration with soil particles. To simplify the system, the self- diffusion of 235 U against 238 U isotopes was considered, such that speciation and sorption environments were constant. Rates of self-diffusion of these isotopes were measured in four contrasting soils, together with the components of the soil U diffusion coefficient. The results showed that U diffusion was controlled by sorption processes in all the soils, and that slow local-equilibration processes had a major effect. The concentration-distance profiles of U in the soils could not be explained with a simple model assuming instantaneous solid:solution equilibration, and some U spread far further than predicted for equilibrium sorption. Differences in U sorption between the soils were not simply related to differences in soil pH, clay content, CEC or mineralogy. To investigate biotic effects, rates of bulk diffusion of U were measured in sterilised soil, and soil in which prokaryotes or eukaryotes were inhibited by biocides. Slow local-equilibration processes were again found to affect diffusion, but transport was also somewhat increased by biotic processes, hypothesised to be due to differences in CO2 pressure arising from microbial activity and thereby U speciation. This has implications for the effects of perturbation on rates of U transport through soil.Item Open Access The impacts of a large-scale conversion to organic agriculture in England and Wales(2017-07) Smith, Laurence G.; Williams, Adrian; Kirk, Guy; Pearce, BruceWith the need to identify sustainable modes of food production for growing populations there has been a growing interest in the potential of organic farming. Although evidence suggests that organic systems can produce food in an environmentally efficient manner, the impacts of a widespread conversion to organic management are still uncertain. The research presented aimed to address this knowledge gap by completing a comprehensive and robust assessment of the food production, fossil energy-use and greenhouse gas impacts associated with a 100% conversion to organic farming in England and Wales. Firstly a structured literature review was carried out to determine the relative fossil-energy efficiency of organic systems. The sustainability of typical organic crop rotations was then assessed using a simulation model of crop-soil N dynamics. Land-use and production scenarios under 100% organic management were assessed through the development and application of a large-scale linear programming model that estimates levels of production under biophysical constraints, e.g. N supplies from biological fixation by legumes. A life-cycle assessment-based model was then applied to explore the extent to which a 100% conversion to organic farming could lead to improvements in greenhouse gas mitigation and fossil energy efficiency. The environmental assessment approach allowed for processes inside and outside of the immediate boundaries of the production systems to be assessed, with the question “what is affected by the change in levels of production?” asked throughout the process. The results revealed that whilst some organic systems offer improved performance in non-renewable resource use efficiency, a widespread conversion would result in a substantial decrease in domestic food production. Total food output expressed over five major food groups fell to 64% of a non-organic baseline. An increase in food imports would therefore be required to meet demand. From a greenhouse gas perspective, a 100% conversion to organic farming in England and Wales could lead to 6% decrease in the impacts of food production. The greenhouse gas mitigation potential of organic farming is strongly related to the use of clover and other legumes in place of manufactured N and lower concentrate feed rates in livestock production. Where the additional-land required under an organic scenario is newly cultivated, it is likely that any greenhouse gas benefit obtained would be offset. Total greenhouse gas emissions increased by an average of 28%, compared to a non-organic baseline, when the land use change impacts associated with increased food imports were included. When the soil carbon sequestration benefits obtained through organic farming are also included the net difference between the two production systems is lessened, however a fundamental question remains concerning the availability of overseas land (land use requirements under organic management increased by 29-47% depending on the scenario). Reducing the area of fertility-building ley within organic rotations is likely to improve productivities and reduce land-use requirements within organic farming systems. Improving crop cultivation practices, more effective cover-cropping and improved biological N-fixation could also help to improve N efficiency and productivity within organic systems. Changes to international organic standards in some areas may also improve the environmental sustainability of the sector, e.g. by allowing recycling of P from sewage treatment. Overall the research showed that whilst the adoption of organic farming can lead to improvements in environmental performance, a widespread conversion would need to be accompanied by substantial changes in diet and/or typical organic practices to become feasible from the perspectives of environmental impact and total food production.Item Open Access Life cycle assessment of land-based greenhouse gas removal technologies.(2021-06) Lefebvre, David; Williams, Adrian; Kirk, GuyGreenhouse gas removal technologies (GGRT) are needed to meet the UNFCCC aim to limit the global average temperature increase to 2°C above pre-industrial levels. GGRTs vary in carbon sequestration potential, readiness level, scalability, cost, required surrounding environment and related environmental and social effects. Quantifying these components in every context is critical to ensure maximum greenhouse gas removal efficiency while minimising negative effects. In this thesis I use life cycle assessment (LCA) to assess the carbon sequestration potential of three GGRTs: enhanced weathering, biochar and reforestation. I use case studies in São Paulo, Brazil for biochar and enhanced weathering, and in the Peruvian Amazon for reforestation. In addition, I use LCA to identify the most important processes in each system and to determine context-specific limits that switch the systems from net GHG sequestration to net GHG emission. Overall, this work promotes the use of LCA to consider GGRTs in their entirety and predict their context-specific carbon capture potential, along with their limitations and potential caveats to guide both the science and policy communities. This thesis was made possible thanks to funding through the SOILS-R-GGREAT (NE/P019498/1) project of the greenhouse gas removal (GGR) program. The GGR program is financed by the UK Natural Environment Research Council (NERC), Engineering and Physical Science Research Council (EPSRC), Economic and Social Science Research Council (ESRC) and the UK department for Business, Energy and Industrial Strategy (BEIS).Item Open Access Measurement of soil respiration and its isotope signature using an automated closed-chamber system(Cranfield University, 2014-06) Downie, Matthew; Kirk, Guy; Pawlett, MarkA variety of methods is currently used for measuring soil and plant respiration and its isotope composition. Limitations found in the literature show a lack of a single set of specifications for these measurements. This report details a unique laboratory at Cranfield University (the Wolfson Field Laboratory - WFL) containing automated gas flux chambers attached to planted soil lysimeters and capable of providing near continuous measurements of gas fluxes and their isotope composition. The research in this thesis was concerned with the ability of the WFL to measure CO2 gas fluxes from plants and soil and their isotope composition. A specification for closed chamber methods was developed, the validity of these specifications tested, and the ability of the WFL to meet these specifications determined. The methods developed include a means of assessing the effects of gas loss processes both on the measured CO2 concentration and the measured isotopic signature within a defined volume. Measurements of plant and soil CO2 efflux in the WFL lysimeters and its isotope composition were used to infer the isotope signature of plant and soil respiration using Keeling plots. The results showed the specifications developed were valid although further work is required to determine the ability of the WFL to meet the isotope measurement specifications.Item Open Access Models and underlying data for 'Soil carbon dioxide venting through rice roots'(Cranfield University, 2019-08-09 10:24) Kirk, Guy; Boghi, AndreaSource codes for the gas formation and transport model described in the paper, written in FORTRAN90 and MATLAB. Kirk G.J.D., Boghi A., Affholder M.C., Keyes S.D., Heppell J. & Roose T. (2019) Soil carbon dioxide venting through rice roots. Plant Cell Environ, doi: 10.1111/pce.13638Item Open Access A soil organic carbon indexing and measurement system(Cranfield University, 2021-10) Prout, Jonah Matthew; Kirk, Guy; Haefele, Stephan M.Soil organic carbon (SOC) is an important component of soils for the various goods and services that soils perform. But SOC stocks have declined significantly in soils around the world over many years due to poor land management. To enable land managers and policy makers to manage SOC better, simple guideline values and measures of SOC concentration are needed. An index based on the SOC to clay concentration ratio as related to soil structural conditions was tested for soils across England and Wales using data from the National Soil Inventory (NSI). Threshold values of SOC/clay equal to 1/8, 1/10 and 1/13 indicated Very Good, Good, Moderate and Degraded levels of SOC. Land use was a driver of SOC/clay ratio, with 38% of arable soils classed as Degraded compared with < 7% of permanent grass or woodland soils. To examine how SOC/clay ratios have been changing over time, I analysed data from resampled sites in the NSI (mean interval of 15 years). The Very Good class was particularly vulnerable to losses compared with other classes. This finding agrees with SOC protection being limited by soil clay concentration. Long-term experiments on soils of contrasting clay concentration showed that the index was sensitive to management activities. In further work I explored the use of dry soil spectral analysis to measure SOC and clay concentrations. I compared dry spectral and conventional wet laboratory analyses of soils in the NSI and in the US National Soil Survey Center-Kellogg Soil Survey Laboratory spectral library (NSSC-KSSL). The NSSC-KSSL results, and to a lesser extent the NSI results (which used older, less-accurate wet laboratory analyses), showed that the technique is suitable for assigning soils to Very Good, Degraded, or Good/Moderate ranges. The index provides quantitative guideline concentrations for SOC with a functional basis and scope for rapid assessment.Item Open Access Source data for a study exploring production impacts of a 100% organic conversion in England and Wales(Cranfield University, 2018-05-13 21:34) Smith, Laurence; Jones, Philip; Kirk, Guy; Pearce, Bruce; Williams, AdrianUnderlying data for ‘Modelling the production impacts of a widespread conversion to organic agriculture in England and Wales’ by L.G. Smith et al. (2018). We develop and apply a bespoke model, the Optimal Land Use Model (OLUM) to estimate levels of production from agriculture in England and Wales under organic management . Outputs under a range of scenarios are compared to the real-world distribution of conventional production in 2010.Item Open Access Tansport processes controlling uranium uptake by plants(Cranfield University, 2018-11) Darmovzalova, Jana; Kirk, Guy; Otten, WilfredThe mechanisms of uranium (U) uptake by plants growing in contaminated soils are poorly understood, constraining the development of mitigation measures and models of U fate and behaviour. Uptake involves a complex interaction between diffusion and reaction processes in the rhizosphere, and root-induced changes in the soil affecting these processes. This thesis is concerned with developing better understanding of these processes, as represented in predictive mathematical models. Most past research on U transport and reaction in soils has been in shaken suspensions or flow-through systems, in which the rate-limiting processes are artificially altered. This thesis develops a novel experimental approach in which diffusion and reaction are measured simultaneously in soil with stationary pore water, better representing the rhizosphere. Concentration- distance profiles of U were measured between two half-cells of soil, one of which initially contained U and the other not, giving rates of desorption in the source and adsorption in the sink cell. The effects of typical root-induced changes in soil pH and CO₂ pressure were measured. Two models were compared: (a) an analytical solution of the appropriate diffusion equation with a constant diffusion coefficient, and (b) a numerical solution allowing for time- and concentration-dependent diffusion. The model parameters were measured or otherwise estimated independent of the concentration-distance profiles. The simple analytical solution correctly accounted for the effects of pH and CO₂ pressure on U diffusion, but under-predicted the diffusive flux. The numerical model correctly predicted the flux and concentration-distance profiles, including a discontinuity at the source-sink boundary due to differences in the kinetics of desorption and adsorption. The results show the importance of correctly allowing for the effects of pH, CO₂ pressure and sorption kinetics in modelling U uptake by plant roots. The model should be further corroborated in mesocosm, half-cell and field experiments, and by verifying U speciation.