CERES :: Browsing by Author "Ritz, K."

Browsing by Author "Ritz, K."

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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.
Open Access
Competitive exclusion as a means to reduce Escherichia coli regrowth in digested sludge
(Cranfield University, 2014-09) Williams, Tyson; Harris, Jim A.; Tyrrel, Sean; Ritz, K.
In recent years, it has been reported that numbers of Escherichia coli increase significantly following centrifugation of sludge during the treatment process. E. coli is used as an indicator of the microbiological quality of sludge-derived products destined for agricultural recycling and of the efficacy of the sludge treatment processes. The re-growth phenomenon is of concern because of the potential for additional treatment requirement / higher disposal costs and loss of consumer confidence associated with a compliance failure. It is hypothesised that a competitive exclusion treatment could be the solution wherein the digestate be exposed to a ‘probiotic’ or defined mixture of micro-organisms, to effectively out compete or eliminate any resident E. coli remaining following treatment. The competitive exclusion principle as a treatment method has already seen application in various industrial sectors, the most well-known being the poultry industry. In experiments it was determined that an antimicrobial producing organism would be most likely to succeed. From the candidates screened, Lactobacillus reuteri proved the most promising. L. reuteri is a known producer of reuterin in the presence of glycerol and organic acids as a part of its normal metabolic activity. In sludge derived nutrient broth in the presence of glycerol and low pH, L. reuteri addition resulted in a reduction of E. coli to undetectable levels. In sludge cake under the same conditions, L. reuteri was less successful. However the addition of glycerol and L. reuteri to sludge cake restricted E. coli growth to a 2 log increase from the initial concentration of E. coli recorded following pasteurisation (an average of around 1x102 cfu/gDs), in comparison in the positive control a 4 log increase was recorded. From this result the sludge cake could be defined as conventionally treated. It can be concluded that competitive exclusion and L. reuteri show promise as a treatment for reducing E. coli re-growth in sludge cake
Open Access
Design, construction and testing of an ascending micropenetrometer to measure soil crust resistance
(Cranfield University, 2014-02) Lorentz, Andrew; Brennan, Feargal; Collu, Maurizio; Ritz, K.
The increasing world population is putting pressure on global food production. Agriculture must meet these growing demands by increasing crop yields. One phenomenon which prevents seedling emergence and damages crop yield is soil crusting. Understanding of soil crusting and the factors which influence it is fundamental to ensuring good crop production. An instrument which will test soil crust strength in a novel way, mimicking seedling growth, may lead to pre-emptive agricultural soil management which could increase crop production. This work details the process of design, construction and testing of an ascending penetrometer to measure soil crust strength. The full design process is discussed from concept generation and evaluation, using experimental methods and a multi-criteria decision making tool, through to final design configuration, specification, manufacture and testing. Traditionally, soil penetrometers measure soil strength by forcing a probe from the surface of the soil into the bulk soil below. To more accurately measure the direct impedance a seedling would experience a device should measure impedance from the bulk soil upwards and into the soil crust, mimicking what a growing seedling would experience. Results prove that the manufactured ascending penetrometer with a force resolution of 0.01N and displacement resolution of 0.0004mm is capable of detecting differences in soil crusts. At these resolutions and accuracy to 0.1N and 0.1mm excellent repeatability was achieved. The machine is therefore a useful and realistic tool for quantitatively comparing soil crusts in soil. It is hoped that being able to compare soil crust strength will lead to improved soil management techniques.
Open Access
The ecology and control of earthworms on golf courses
(Cranfield University, 2006-12) Bartlett, Mark D.; Ritz, K.; Harris, Jim A.; James, Iain
Earthworm casts on golf courses affect the playability of the turf and can potentially damage mowing equipment. Traditionally this problem has been limited using chemical controls. It is estimated that 0.6% of the total UK land surface is occupied by golf courses, therefore, the land management strategies which green keepers adopt with respect to the application of chemicals has a major environmental impact. The aim of this thesis was to investigate the ecology and potential control of earthworm casting in golf turf in environmentally sustainable ways. A quadrat survey of earthworm casts was conducted over two years at five golf courses in Bedfordshire and Buckinghamshire, UK. Using generalized linear models and forward multiple stepwise regression, an internally validated predictive model of earthworm casting activity was constructed. Annual activity on surfaces was predicted using five physicochemical parameters of which C: N and total inorganic nitrogen were the most important. Environmental parameters were also used to predict monthly earthworm activity, with evapotranspiration and rainfall representing the most significant variation. ' Mustard extraction surveys were used to investigate species diversity and community structure of earthworms. Four dominant species were identified (Aporrectodea rosea, Lunibricus rubellus, Aporrectodea longa and Lumbricus terrestris). It is likely that A. longa and L. terrestris, the two must abundant anecic forms, cause the greatest problems to green keepers as these are the largest of the four earthworm species. The microbial community of soil represents the earthworm's primary food source. An analysis of the microbial community size (using chloroform-extraction) and community structure (using phospholipid fatty acid [PLFA] analysis) showed that different surfaces found on golf courses supported significantly distinct and consistent microbial communities. Differences in population size and structure were evident at different depths through all golf course soil profiles investigated. Individual surface types were comparable, irrespective of geographical location. Therefore different surfaces and depths through the soil profile on golf courses represent different earthworm habitats. An investigation of the effects of different construction techniques and materials used in the golf industry on the rate of earthworm cast formation was made. This showed no effect of construction on the vertical distribution of earthworms, but the rate of casting increased on the sand dominated surfaces. It is proposed that this is due to the lower calorific value that this soil represents to the earthworms. This knowledge was applied in an earthworm cast mitigation experiment, reducing casting rates by stimulating the size of the microbial community with glucose solution. Control through physical exclusion of earthworms to the surface using a buried mesh was also trialled and significantly reduced earthworm casts, however no causal mechanism could be elucidated. This study has advanced the understanding of earthworm ecology on golf courses, deriving mechanistic understandings of this system as a whole. This will lead to a more environmentally sustainable approach to the control of earthworms on golf courses.
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.
Open Access
Engineering difference: Matrix design determines community composition in wastewater treatment systems
(Elsevier Science B.V., Amsterdam., 2012-03-01T00:00:00Z) Harris, Jim A.; Baptista, J. D. C.; Curtis, T. P.; Nelson, A. K.; Pawlett, Mark; Ritz, K.; Tyrrel, Sean F.
There is a growing view that the application of ecological theory has the potential to facilitate a transition from a descriptive to a predictive framework in wastewater engineering. In this study we tested the hypotheses that: (i) it is possible to engineer consistent differences between microbial communities in wastewater treatment modules; (ii) there is a positive relationship between structural complexity and genetic diversity; (iii) such interactions are modulated by the availability of energy. We developed four treatment modules of increasingly complex support material (matrix) design, and pumped a synthetic wastewater through them for 16 weeks. We then disassembled the modules and assessed the phylogenetic (general eubacteria and ammonium diversity of the communities present on the support materials. We found that different genotypic and phenotypic community structures were reliably generated by the engineering of their physical environment in terms of structural complexity (as determined by particle size distribution and therefore pore size distribution). Furthermore, there was a notably consistent response of the phenotypic structure to such circumstances, and also to the presence of organic matter. However, we found no significant relationships between genetic diversity and structural complexity either for eubacterial or ammonia-oxidiser microbial groups. This work demonstrates that is it possible to engineer modules of differing microbial community composition by varying their physical complexity. This is an essential first step in testing relationships between system diversity and treatment resilience at a process level.oxidisers, by DGGE profiling) and phenotypic (by PLFA profiling)
Open Access
Evaluation of factors affecting the quality of compost made by smallholder farmers in Malawi
(Cranfield University, 2007-02) Nalivata, Patson Cleopus; James, Iain; Ritz, K.
In Malawian agriculture, the use of compost as a soil amendment has received much attention over the last few decades. Despite this, little is known about the commonly practiced composting systems in Malawi and their potential in mitigating soil fertility problems experienced by smallholder farmers. This study characterized the Changu (turned and watered regularly) and Chimato (covered with mud and static) systems and investigated optimum conditions required for effective composting. It further investigated nutrient release characteristics of the composts from these systems and their impact on maize crop establishment. Replicated compost heaps were formed from wheat (Triticum aestivum) straw and grass /clover (Lolium perenne/Trifolium repens) (in the UK) and maize (Zea mays L.) straw and green bean (Phaseolus vulgaris L.) residue (in Malawi) using the Changu and Chimato systems. Four initial C:N ratios of 20:1, 25:1, 30:1 and 60:1 were studied in the UK whereas two initial C:N ratios of 20:1 and 30:1, chopped into two lengths (5 or 10 cm) were used in Malawi. All the treatments were set in a randomized complete block design and the composting experiments ran for 112 days in the UK study and for 77 days in Malawi. Incubation-mineralization studies using the resultant composts were run for 42 days and 84 days for UK and Malawi respectively, followed by a maize establishment study run for 25 days. The Changu systems had significantly longer mesophilic phases (19 days) and active composting periods (24 days) compared to the Chimato systems (14 and 22 days respectively). The temperature profiles for the two systems were similar in the glasshouse, but differed in the field due to reduced insulation in the Changu (uncovered) system. The composting processes in these systems contributed to the production of compost with as high as 1.1% total N. A higher concentration of NO3-N (406 mg/kg dwt.) was produced in the Changu system cf. Chimato (359 mg/kg dwt.) whereas a higher concentration of NH4-N (36 mg/kg dwt.) was produced in the Chimato system cf. Changu (34 mg/kg dwt.) for the Malawi compost. Similarly, Changu system resulted in greater concentrations of TON (61 mg/kg dwt.) cf. Chimato (24 mg/kg dwt.) whilst Chimato contained high concentration of NH4-N (61 mg/kg dwt.) cf. Changu (8 mg/kg dwt.) for the UK compost. No differences were observed in the concentration of extractable-P and extractable-K in the two systems for the UK studies whereas Changu treatments and those from initial C:N had more P in Malawi. Resultant compost pH ranged between 6.8 and 8.6 for the UK-based studies and between 7.2 and 8.9 for the Malawian-based study. Incubation-mineralization studies indicated temporal differences when the resultant compost from the two systems (Changu and Chimato) was incubated in the soil with respect to nutrient release. Initial feedstock C:N ratio had a significant effect, treatments with C:N 20:1 mineralized nitrogen whilst those with initial C:N 30:1 and 60:1 immobilized nitrogen compared to the control for the UK experiments. No immobilization was observed for Malawi resultant compost. This was reflected in the maize establishment trials when compost from the two systems was used as a soil amendment. Treatment with materials from initial C:N 20:1 produced significantly larger plant stalks and high plant biomass (0.92 g/plant (dry basis)) than the other treatments. Varied differences were observed between UK and Malawi with respect to composting system on plant growth. The use of compost from this study increased CEC of the soil by 2.1 cmol/kg. Efficient composting requires low C:N material and the required compost time and resultant quality is dependent upon the C:N ratio of the initial feedstock. The longer active composting time in the Changu systems appeared to influence production of TON compared to the Chimato. It is suggested that to optimise the compost quality there is a need to encourage the smallholder farmers to grow green leguminous crops which they can mix with the straw to reduce the initial C:N ratio to improve its compostability. It is also important to increase the number of aeration holes in the mud coat of the Chimato heap in order to improve the oxygenation process of the material and to use them for moisture adjustments. A cost benefit analysis conducted suggested that the lower the initial C:N ratio and the longer the chop length (≤ 10 cm), composting using the Changu system, the higher the net benefits which can be attained.
Open Access
Evidence for functional state transitions in intensively-managed soil ecosystems
(Nature Publishing Group, 2018-08-01) Todman, L. C.; Fraser, F. C.; Corstanje, Ronald; Harris, Jim A.; Pawlett, Mark; Ritz, K.; Whitmore, A. P.
Soils are fundamental to terrestrial ecosystem functioning and food security, thus their resilience to disturbances is critical. Furthermore, they provide effective models of complex natural systems to explore resilience concepts over experimentally-tractable short timescales. We studied soils derived from experimental plots with different land-use histories of long-term grass, arable and fallow to determine whether regimes of extreme drying and re-wetting would tip the systems into alternative stable states, contingent on their historical management. Prior to disturbance, grass and arable soils produced similar respiration responses when processing an introduced complex carbon substrate. A distinct respiration response from fallow soil here indicated a different prior functional state. Initial dry:wet disturbances reduced the respiration in all soils, suggesting that the microbial community was perturbed such that its function was impaired. After 12 drying and rewetting cycles, despite the extreme disturbance regime, soil from the grass plots, and those that had recently been grass, adapted and returned to their prior functional state. Arable soils were less resilient and shifted towards a functional state more similar to that of the fallow soil. Hence repeated stresses can apparently induce persistent shifts in functional states in soils, which are influenced by management history.
Open Access
Facilitating ecosystem assembly: Plant-soil interactions as a restoration tool
(Elsevier, 2018-02-23) van der Bij, A. U.; Weijters, M. J.; Bobbink, R.; Harris, Jim A.; Pawlett, Mark; Ritz, K.; Benetková, P.; Moradi, J.; Frouz, J.; van Diggelen, Rudy
Although plant-soil interactions are increasingly recognized as an important factor in ecosystem restoration, their effects on community assembly during de novo ecosystem establishment are largely unknown. In a heathland restoration trial after topsoil removal we introduced either only aboveground heathland species with fresh herbage or both above- and belowground heathland species with sods to facilitate community assembly. Sod inoculation increased resemblance of the microbial community to the reference system, with a higher fungal and lower bacterial proportion to the community structure. Also densities of bacteriophagous and phytophagous nematodes, Acari and Collembola increased after sod inoculation. The cover of heathland plant species increased by 49% after sod inoculation. The introduction of solely aboveground heathland species increased the cover of these species by only 13%, and did not affect soil community assembly. Additionally, the increase in cover of heathland species over time was inversely correlated to the cover of mesotrophic grassland species. Inverse correlations were also observed between changes in fungal and bacterial abundances. Simultaneous introduction of key species of both above- and below-ground communities had a critical effect on the establishment of both communities, providing a potential shortcut for successful restoration of target ecosystems on disturbed soils.
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.
Open Access
The impact of anecic earthworms on the dispersal of Microdochium nivale in amenity sports turf
(Cranfield University, 2012-09) Young, Matt; Ritz, K.; James, Iain; Tibbett, Mark
In sports surface management, integrated disease management (IDM) is useful in identifying the parameters for which disease can occur. The host, pathogen and environment are factors that are intrinsically linked for disease to manifest. When either of these causal components is not present then plant disease is prevented. Soil biotas have been implicated in the movement of pathogenic soil microbes through both consumption and ejection and by external contamination, the propagule attaching itself to the external wall of the earthworm. Soil biota could therefore be included as a causal factor in disease development. The aim of this thesis was to investigate the impact anecic earthworms have on the dissemination of Microdochium nivale in amenity sports turf. An initial experiment to ascertain viability of M. nivale spores post ingestion through Lumbricus terrestris was performed. Sterilised soil pre-inoculated with M. nivale was fed to earthworms and propagules re-isolated from the faecal matter using a soil dilution technique. Results showed that 10% of viable propagules of M. nivale fed to earthworms survived the digestion process and were evident in the faecal matter (cast). A turf microcosm experiment was established to record whether the casts containing propagules of M. nivale could lead to infections of Fusarium patch, the plant disease caused by M. nivale in amenity turf. Spiked casts (M. nivale) were placed in pots containing Lolium perenne and the incidence and severity of disease was recorded using image analysis. The conclusions were that the spiked cast material was no more infectious than spore solutions of M. nivale inoculated onto the plant material. A final investigation of the effects the presence and absence of earthworms have on the dissemination of M. nivale propagules in turf grass was conducted. Turf microcosms containing Agrostis stolonifera were pre-inoculated with a spore solution of M. nivale in either the presence or absence of earthworms. Rate and progression of disease was recorded using image analysis, dispersal of propagules was assayed through leaf sampling in the microcosm. Results indicated that the presence of earthworms had a greater effect on both the manifestation of Fusarium patch, and the dispersal of M. nivale propagules than in the absence of earthworms. This study has provided a contribution to understanding the interactions between L. terrestris and M. nivale. It is clear that earthworm interaction with M. nivale enhances the dispersal of viable propagules, potentially leading to fresh manifestation of disease. Recommendations regarding the management of terrestris, already considered a nuisance on fine turf due to its casting; would be to mitigate these earthworms in areas of intensively managed turf, whereby the advantages of high earthworm activity are neither necessary nor required.
Open Access
Indicators of soil quality - Physical properties (SP1611). Final report to Defra
(Defra, 2012-09-30) Rickson, R. Jane; Deeks, Lynda K.; Corstanje, Ronald; Newell-Price, Paul; Kibblewhite, Mark G.; Chambers, B.; Bellamy, Patricia; Holman, Ian P.; James, I. T.; Jones, Robert; Kechavarsi, C.; Mouazen, Abdul; Ritz, K.; Waine, Toby
The condition of soil determines its ability to carry out diverse and essential functions that support human health and wellbeing. These functions (or ecosystem goods and services) include producing food, storing water, carbon and nutrients, protecting our buried cultural heritage and providing a habitat for flora and fauna. Therefore, it is important to know the condition or quality of soil and how this changes over space and time in response to natural factors (such as changing weather patterns) or to land management practices. Meaningful soil quality indicators (SQIs), based on physical, biological or chemical soil properties are needed for the successful implementation of a soil monitoring programme in England and Wales. Soil monitoring can provide decision makers with important data to target, implement and evaluate policies aimed at safeguarding UK soil resources. Indeed, the absence of agreed and well-defined SQIs is likely to be a barrier to the development of soil protection policy and its subsequent implementation. This project assessed whether physical soil properties can be used to indicate the quality of soil in terms of its capacity to deliver ecosystem goods and services. The 22 direct (e.g. bulk density) and 4 indirect (e.g. catchment hydrograph) physical SQIs defined by Loveland and Thompson (2002) and subsequently evaluated by Merrington et al. (2006), were re-visited in the light of new scientific evidence, recent policy drivers and developments in sampling techniques and monitoring methodologies (Work Package 1). The culmination of these efforts resulted in 38 direct and 4 indirect soil physical properties being identified as potential SQIs. Based on the gathered evidence, a ‘logical sieve’ was used to assess the relative strengths, weaknesses and suitability of each potential physical SQI for national scale soil monitoring. Each soil physical property was scored in terms of: soil function – does the candidate SQI reflect all soil function(s)? land use - does the candidate SQI apply to all land uses found nationally? soil degradation - can the candidate SQI express soil degradation processes? does the candidate SQI meet the challenge criteria used by Merrington et al. (2006)?This approach enabled a consistent synthesis of available information and the semi-objective, semi-quantitative and transparent assessment of indicators against a series of scientific and technical criteria (Ritz et al., 2009; Black et al., 2008). The logical sieve was shown to be a flexible decision-support tool to assist a range of stakeholders with different agenda in formulating a prioritised list of potential physical SQIs. This was explored further by members of the soil science and soils policy community at a project workshop. By emphasising the current key policy-related soil functions (i.e. provisioning and regulating), the logical sieve was used to generate scores which were then ranked to identify the most qualified SQIs. The process selected 18 candidate physical SQIs. This list was further filtered to move from the ‘narrative’ to a more ‘numerical’ approach, in order to test the robustness of the candidate SQIs through statistical analysis and modelling (Work Package 2). The remaining 7 physical SQIs were: depth of soil; soil water retention characteristics; packing density; visual soil assessment / evaluation; rate of erosion; sealing; and aggregate stability. For these SQIs to be included in a robust national soil monitoring programme, we investigated the uncertainty in their measurement; the spatial and temporal variability in the indicator as given by observed distributions; and the expected rate of change in the indicator. Whilst a baseline is needed (i.e. the current state of soil), it is the rate of change in soil properties and the implications of that change in terms of soil processes and functioning that are key to effective soil monitoring. Where empirical evidence was available, power analysis was used to understand the variability of indicators as given by the observed distributions. This process determines the ability to detect a particular change in the SQI at a particular confidence level, given the ‘noise’ or variability in the data (i.e. a particular power to detect a change of ‘X’ at a confidence level of ‘Y%’ would require ‘N’ samples). However, the evidence base for analysing the candidate SQIs is poor: data are limited in spatial and temporal extent for England and Wales, in terms of a) the degree (magnitude) of change in the SQI which significantly affects soil processes and functions (i.e. ‘meaningful change’), and b) the change in the SQI that is detectable (i.e. what sample size is needed to detect the meaningful signal from the variability or noise in the signal). This constrains the design and implementation of a scientifically and statistically rigorous and reliable soil monitoring programme. Evidence that is available suggests that what constitutes meaningful change will depend on soil type, current soil state, land use and the soil function under consideration. However, when we tested this by analysing detectable changes in packing density and soil depth (because data were available for these SQIs) over different land covers and soil types, no relationships were found. Schipper and Sparling (2000) identify the challenge: “a standardised methodology may not be appropriate to apply across contrasting soils and land uses. However, it is not practical to optimise sampling and analytical techniques for each soil and land use for extensive sampling on a national scale”. Despite the paucity in data, all seven SQIs have direct relevance to current and likely future soil and environmental policy, because they can be related (qualitatively) to soil processes, soil functions and delivery of ecosystem goods and services. Even so, meaningful and detectable changes in physical SQIs may be out of time with any soil policy change and it is not usually possible to link particular changes in SQIs to particular policy activities. This presents challenges in ascertaining trends that can feed into policy development or be used to gauge the effectiveness of soil protection policies (Work Package 3). Of the seven candidate physical SQIs identified, soil depth and surface sealing are regarded by many as indicators of soil quantity rather than quality. Visual soil evaluation is currently not suited to soil monitoring in the strictest sense, as its semi-qualitative basis cannot be analysed statistically. Also, few data exist on how visual evaluation scores relate to soil functions. However, some studies have begun to investigate how VSE might be moved to a more quantified scale and the method has some potential as a low cost field technique to assess soil condition. Packing density requires data on bulk density and clay content, both of which are highly variable, so compounding the error term associated with this physical SQI. More evidence is needed to show how ‘meaningful’ change in aggregate stability affects soil processes and thus soil functions (for example, using the limited data available, an equivocal relationship was found with water regulation / runoff generation). The analysis of available data has given promising results regarding the prediction of soil water retention characteristics and packing density from relatively easy to measure soil properties (bulk density, texture and organic C) using pedotransfer functions. Expanding the evidence base is possible with the development of rapid, cost-effective techniques such as NIR sensors to measure soil properties. Defra project SP1303 (Brazier et al., 2012) used power analyses to estimate the number of monitoring locations required to detect a statistically significant change in soil erosion rate on cultivated land. However, what constitutes a meaningful change in erosion rates still requires data on the impacts of erosion on soil functions. Priority cannot be given amongst the seven SQIs, because the evidence base for each varies in its robustness and extent. Lack of data (including uncertainty in measurement and variability in observed distributions) applies to individual SQIs; attempts at integrating more than one SQI (including physical, biological and chemical SQIs) to improve associations between soil properties and processes / functions are only likely to propagate errors. Whether existing monitoring programmes can be adapted to incorporate additional measurement of physical SQIs was explored. We considered options where one or more of the candidate physical SQIs might be implemented into soil monitoring programmes (e.g. as a new national monitoring scheme; as part of the Countryside Survey; and as part of the National Soil Inventory). The challenge is to decide whether carrying out soil monitoring that is not statistically robust is still valuable in answering questions regarding current and future soil quality. The relationship between physical (and other) SQIs, soil processes and soil functions is complex, as is how this influences ecosystem services’ delivery. Important gaps remain in even the realisation of a conceptual model for these inter-relationships, let alone their quantification. There is also a question of whether individual quantitative SQIs can be related to ecosystem services, given the number of variables.
Open Access
Interactions between microbial community structure and pathogen survival in soil
(Cranfield University, 2012-01) Moynihan, Emma Louise; Ritz, K.; Tyrrel, Sean; Richards, Karl; Brennan, Fiona
Manure and slurry are valuable resources that may enhance many soil properties. However, organic amendments can pose a significant health risk to both humans and livestock if not managed correctly due to pathogenic loads that may be carried within them. Therefore it is crucial to identify the factors that affect pathogen survival in soil, in order to gain maximum benefit from such resources, whilst minimising the threat to public and animal welfare. This research aimed to elucidate the impact of microbial community structure on pathogen decline following entry to such organisms into the soil. It was hypothesised that pathogen survival would be significantly influenced by both diversity and phenotypic configuration of the microbial community. This was experimentally investigated within three distinctly different biological contexts. Cont/d.
Open Access
Interactions between phosphorus fertilisation and soil biota in managed grasslands systems
(Cranfield University, 2012-05) Massey, Paul Andrew; Creamer, Rachel E.; Ritz, K.
The application of phosphorus (P) fertilisers to grassland systems is a common practice to increase and sustain grassland productivity. This is requisite for satisfying the nutritional needs of grazing animals and increasing dairy and livestock output. The costs of such fertilisers are increasing and the demands for such fertiliser will also most likely rise following governmental targets set in Ireland to increase national agricultural output. However, the application of P fertiliser to grassland systems can contribute to the eutrophication of water-courses, since fertiliser applications can result in the accumulation of P at the soil surface. One potential way to facilitate plant P acquisition in grasslands may be associated with the soil biota. In particular, the soil microbial biomass is recognised as a potential P pool that can provide a source of bioavailable P to the plant community. The soil biota may also facilitate the incorporation of P from the soil surface into the soil profile, since earthworms can actively increase the transport of P-rich soil material from the surface belowground. This project thus aimed to discern how P fertilisation affects microbial biomass nutrient pools and biologically-mediated P incorporation in grassland systems, and how this relates to plant P yields. To investigate this aim, two research questions were proposed: (i) is the soil biota affected by commonly adopted P fertiliser strategies in grassland systems?; (ii) what consequence does this hold for P acquisition by the plant community? An experiment was conducted to examine how the soil biota responded to different rates of inorganic P fertilisation in two grassland sites of contrasting soil types over an 18 month period. This revealed that increasing P fertilisation did not affect microbial biomass P concentrations in the soil. However, an effect was observed upon plant P yield, in which greater plant P yields were obtained proportional to the P fertiliser rate. Two laboratory experiments were conducted to further investigate this lack of effect. These utilised soil from the same grassland sites and examined how nutrient additions to the soil affected microbial biomass nutrient pools and activity. Results from these experiments supported evidence from the field experiment, since the application of P fertiliser did not affect microbial biomass nutrient pools following fertiliser application, and supplementation of carbon (C) + P substrate to the soil did not invoke respiratory responses between P fertiliser treatments. Nevertheless,supplementation with C + nitrogen (N) and C+N+P substrates was found to suppress microbial respiration. This was attributed to greater C assimilation by the microbial community in these particular substrate-induced respiration treatments. In order to investigate biologically-mediated P incorporation, a glasshouse-based mesocosm scale experiment was carried out using two contrasting soils. Bulk soil (1 – 30 cm depth range) was derived from a nutrient poor grassland system, whereas the soil for the 0 – 1 cm depth range was taken from an intensive system that was seven times greater in labile inorganic P concentration. Three treatments were applied to mesocosms in an incomplete factorial design, involving the inclusion of earthworms, different botanical diversities (unplanted, monoculture or mixed plant community) and different fertiliser types (organic or inorganic). The absent factorial combinations involved the application of earthworms to unplanted mesocosms. With respect to the earthworm treatment, results revealed that the presence of earthworms reduced labile P concentrations in the 0 – 1 cm depth range of soil. The presence of different botanical diversities or fertiliser types did not affect microbial biomass nutrient pools, whilst the presence of mixed plant communities did increase plant P yields. However, microbial and nematode community structures were affected in an idiosyncratic manner by both botanical diversity and fertiliser type. This project demonstrated the significance of grassland management regimes in governing microbial biomass P concentrations. In particular, it was revealed that the frequent defoliation of the sward appeared to uncouple the microbial community from both fertiliser inputs and possibly plant P yields. The fact that an increase in plant P yield with increasing P fertilisation was noted in the absence of microbial responses suggests that the soil biota may not be crucial for plant P acquisition in such intensive inorganic-fertiliser based regimes. This suggestion was also supported by the mesocosm experiment, since plant P yields differed between botanical diversities but no effects were observed on microbial biomass P concentrations. Furthermore, this project showed the potential of the earthworm community to reduce P concentrations in the volume of soil which poses the greatest risk to water quality. The collective evidence highlights the need for further understanding of the consequences of inorganic-based fertiliser management systems, since current strategies may not adequately account for management effects on soil biological P cycling.
Open Access
Interactions between sewage sludge and the survival of pathogenic bacteria in soil
(Cranfield University, 2015-02) Ellis, Stephanie; Ritz, K.; Tyrrel, Sean; Richards, Karl; Griffiths, Bryan; EU FP7 Environment theme
Sewage sludge is a potentially valuable resource that can enhance both the structure and fertility of soil. However, it can also harbour enteric pathogens which pose a significant socio-economic risk to society. Therefore it is important to understand the factors that govern the persistence of such pathogens in soil, when co-introduced with sewage sludge, in order to mitigate risk and to further avail of such a valuable resource. This research aimed to clarify how microbial activity and the presence of sewage sludge would influence the persistence of co-introduced enteric pathogens in soil. It was theorised that the addition of sewage sludge to soil would cause the formation of organic matter (OM) and nutrient-rich niches. Such niches, in turn, would encourage the enhanced activity of the local soil microbial community, instigating greater competition for local resources, i.e. a hot spot of microbial activity that would lead to a decline in the introduced enteric pathogens. It was also hypothesised that the interface between the soil and sewage sludge may influence such interactions, as the physicochemical characteristics could affect the extent of exposure and subsequent interactions between enteric pathogens and the soil microbial community. These theories were investigated using four different perspectives that linked closely with each other. In initial studies, two cohorts of microcosms consisting of different proportions of sewage sludge to soil were inoculated with either E. coli or S. Dublin and destructively sampled over a 42 day period. E. coli prevailed at greater numbers when inoculated directly into soil and sewage sludge, whilst it declined to the greatest extent within mixed microcosms containing 25% sludge. All treatments containing S. Dublin appeared to decline at a similar rate, which was more linear than the decline observed within treatments inoculated with E. coli. From these findings, it can be concluded that there are no direct relationships between the proportion of sludge to soil and its affect on pathogen survival. A subsequent experiment implemented a similar treatment strategy, whilst using indigenous sewage sludge E. coli. The use of this microbe provided data which was more suited to the original premise of this work, as under such scenarios it would be indigenous sewage sludge E. coli that would be of concern. Therefore, microcosms consisting of different proportions of sewage sludge, containing indigenous E. coli, were destructively sampled over a 56 day period. The indigenous sewage sludge E. coli exhibited a more consistent linear decline after the first week. However, the indigenous E. coli were again not significantly affected by different proportions of sewage sludge to soil. It was theorised that this lack of variation in response to varying proportions of sewage sludge to soil may have been associated with a lack of available substrate within the system, or some form of partitioning effect between soil and sewage sludge matrices, which prevented the microbial communities from interacting. To further develop these concepts, the effect of two contrasting substrate amendments and their location (either sewage sludge, soil or within both matrices) was also investigated in relation to the persistence of sewage sludge-derived E. coli. Microcosms consisting of both pure samples and mixtures of sewage sludge or soil were inoculated with sewage sludge-derived E. coli and destructively sampled over a 42 day period. Respired CO2 and microbial carbon were also quantified. The addition of a simple substrate, glucose, instigated a peak in microbial respiration and accelerated the decline of sewage sludge-derived E. coli and also marginally increased the microbial biomass. This is similar to the original concept proposing that a hot spot of microbial activity could instigate pathogen die-off. In contrast, amendment with a more complex substrate, yeast extract, had little effect on the decline of sewage sludge-derived E. coli. Nor did respiration increase immediately after amendment. There was also no observable partitioning effects between soil or sewage sludge with either amendment. This suggests that a lack of available substrate could influence microbial dynamics and thus the decline of E. coli. To further explore this phenomenon the repeated addition of glucose and its effect on the survival of sewage sludge-derived E. coli was investigated. It aimed to highlight the impact of sustained competition for resources on persistence, whilst mimicking the recurrent input of carbon that occurs in plant/soil systems. Microcosms consisting of both pure and mixtures of sewage sludge or soil were inoculated with sewage sludge-derived E. coli and destructively sampled over a period of 105 days. Respired CO2 and microbial carbon were again analysed. It was found that the repeated addition of glucose did not cause a significant decline in the survival of sewage sludge-derived E. coli. Notably, some small increases in E. coli numbers were observed after the second and third amendments of glucose. Overall, these findings suggest that hot spots of activity can instigate a decline in enteric pathogens, though such interactions are dependent upon the availability and quantity of nutrients and organic carbon within the matrices. These findings could aid in developing the use of amendments in sewage sludge that would minimise the survival of enteric pathogens in soil. They also provide a framework which pinpoints the factors that should be considered when investigating the persistence of enteric pathogens in the soil environment. Such amendments and knowledge pertaining to the key factors in the survival of enteric pathogens could further decrease the social and economic risk which the use of sewage sludge poses when used in agricultural systems.
Open Access
Interactions between soil microbial communities, erodibility and tillage practices
(Cranfield University, 2006-12) Allton, Kathryn E.; Harris, Jim A.; Ritz, K.
The soil biota are a vital component of belowground systems, driving many key processes such as nutrient cycling, underwriting soil structural integrity and providing crucial ecosystem services to the wider environment. In agricultural systems, tillage practices are known to impact upon both the soil biota and surface erosion processes, but little is understood about the relationships between these three factors. This work addresses this issue within the framework of an EU Life/ Syngenta project “Soil and water protection for northern and central Europe” (SOWAP). Within this component of the SOWAP programme, the influence of different soil management practices on the size and overall composition of the soil microbial community was determined and related to the propensity for erosion, at a variety of spatial scales. Microbial biomass and phenotypic structure, measured using phospholipid fatty acid (PLFA) analysis, were used to determine the effect tillage had on microbial communities at sites in Belgium, Hungary and the UK. The field sites were split into differing tillage practices on the same slope. Samples were taken prior to, and three years after, the adoption of inversion (conventional) and non-inversion tillage techniques. In addition, samples were taken periodically from two sites in the UK (Loddington, Leicestershire and Tivington, Somerset) to assess the temporal changes in microbial community size and structure under the tillage practices. Other soil, agronomic and ecological properties were measured at the field scale by SOWAP project partners. These field trials were supported by small plot rainfall simulations at the Loddington field site and by laboratory-based microcosm-scale studies using manipulated microbial communities and controlled rainfall, to further characterise microbial effects on soil erodibility. The results showed that across the European sites microbial community size was reduced in conventionally tilled soils. However there was no effect of tillage type on microbial biomass at the Tivington site after three years. Microbial community structure showed significant seasonal changes greater than those relatable to tillage type. It was notable that the fungal biomarker PLFA 18:2ω6 decreased in conventionally tilled soils. The small-scale experimentation using rainfall simulators and manipulated microbial communities was designed to specifically observe relationships between soil microbial communities, water movement and erodibility. These experiments showed that the presence of microbes in soils impacted upon both erosion processes and hydrological properties. There was a trend showing a decreased sediment concentration in runoff from soils containing a living microbial community. Propensity to runoff and infiltration was altered differentially as a result of microbial inocula derived from soils under different tillage practices. There was evidence that there was a specific and characteristic fraction of the microbial community susceptible to mobilisation by runoff and infiltrate waters, and hence potentially prone to relocation within the ecosystem. Linking the laboratory experiments to field rainfall simulations demonstrated the difficulty of controlling environmental variables, particularly at larger scales. Nevertheless, the same basic trends were observed at both laboratory and small plot scales.
Open Access
Is the thermodynamic efficiency of soil microbial communities related to ecosystem maturity and stress?
(Cranfield University, 2014-07) Grice, Samuel M.; Harris, Jim A.; Ritz, K.; National Environmental Research Council(NERC); The Swedish Research Council Formas
According to the second law of thermodynamics, no process can be 100% efficient and all processes must increase the total entropy of the system they occupy. Therefore, living systems require a constant influx of low-entropy energy to survive, giving an evolutionary advantage to those that produce less waste. Odum suggested that ecosystems would therefore develop mechanisms for reducing entropy production per unit biomass, as they matured. Isothermal calorimetry allows the direct measurement of waste heat emitted from any system, including soils and the life within them. However, upon review it became apparent that current methods employed in the analysis of soil microbial communities via isothermal calorimetry are outdated and in need of review. An experiment was conducted to troubleshoot the method and appropriate modifications were made. A second experiment was conducted to test the microbial community response to pre-incubation prior to calorimetric analysis at 20°C, concluding that samples should be pre-incubated for ten to sixteen days prior to analysis at 20°C. Subsequently, experiments were carried out to establish how much waste heat was produced by soil microbial communities in the context of various ecological gradients, following glucose amendment. Results for enthalpy efficiency (ηeff) proved inconclusive, whereas results for substrate induced heat production (SIHP), where heat output is expressed per unit biomass, indicated that soil microbial communities produced significantly more waste heat when subjected to long-term metals induced stress and short-term copper-induced stress. In addition, a reduction in the production of waste heat generated by soil microbial communities associated with primary succession along a glacier foreland was observed. This provides evidence that living systems do indeed evolve towards greater thermodynamic efficiency, manifest via the reduction of energetic waste.
Open Access
The microbiology of arable soil surfaces
(Cranfield University, 2007-10) Jeffery, Simon; Ritz, K.; Harris, Jim A.; Rickson, R. Jane
Whilst much is known about the physics and erosion of soil surfaces on a millimetre scale, little is known about the associated microbiology, particularly in temperate arable systems. The vast majority of research regarding microbial interactions at soil surfaces has concerned microbiotic crusts. However, such surface crusts take many years to form and then only in relatively undisturbed soil systems. Arable soil surfaces are subject to relatively extreme environmental conditions, potentially undergoing rapid changes in relation to temperature, water status and solar radiation compared to deeper soil zones. These extreme environmental parameters are likely to have a large impact on the biota found at the arable soil surface when compared to that which occurs in deeper soil zones. Phenotypic profiling using phospholipid fatty acid (PLFA) analysis, microbial biomass, and chlorophyll concentration were used to characterise soil microbial communities with the aim of quantifying differences within the surface layers of arable systems on a millimetre scale. This field work was supported with a series of microcosm-scale studies in which parameters such as length of time between disturbance events and the quality of light reaching the soil surface were controlled. Using microcosms subjected to simulated rainfall and imaged using X-ray computed tomography scanning, the effects of the soil surface microbiota on associated physical properties including structural integrity, porosity, erodibility and hydrological properties were investigated. This research showed that given sufficient time between disturbance events, environmental parameters such as temperature and wet:dry cycling were sufficient to drive the formation of a distinct soil surface phenotype, which appeared to be consistently confined to an order of depth of circa 1 mm. It was notable that the PLFA 16:0 was consistently associated with discrimination between phenotypes between soil surface layers. Calculation of the ratio of fungal to bacterial PLFA biomarkers showed a consistently higher ratio of fungi to bacteria present in the soil surface layer to a depth of circa 1 mm, providing evidence that fungi grow preferentially over the soil surface compared to through the soil matrix. Further investigation demonstrated that light, particularly at photosynthetically active wavelengths, was the main driving factor in the establishment of the distinct soil surface phenotypes. The inocula which drove the formation of such soil-surface community phenotypes, especially the photoautotrophic components, was demonstrated to derive predominantly from aerial sources. Functionally the nature of the soil surface community was found to affect run-off generation and shear strength at the surface. There was no significant impact of the soil surface microbiota on erodibility or water infiltration rates, although whilst distinct surface phenotypes had developed in this experimental circumstance, these were relatively deficient in photoautotrophs compared to other microcosm experiments and field circumstances, and hence extrapolation of this conclusion is not sound. This project has demonstrated that a soil surface ecological niche may exist in other unexplored soil surfaces and highlights the needs to explore this possibility and to examine any associated functional consequence should such niches be found to exist.
Open Access
A simple reactive-transport model of calcite precipitation in soils and other porous media
(Elsevier, 2015-05-14) Kirk, Guy J. D.; Versteegen, A.; Ritz, K.; Milodowski, A. E.
Calcite formation in soils and other porous media generally occurs around a localised source of reactants, such as a plant root or soil macro-pore, and the rate depends on the transport of reactants to and from the precipitation zone as well as the kinetics of the precipitation reaction itself. However most studies are made in well mixed systems, in which such transport limitations are largely removed. We developed a mathematical model of calcite precipitation near a source of base in soil, allowing for transport limitations and precipitation kinetics. We tested the model against experimentally-determined rates of calcite precipitation and reactant concentration–distance profiles in columns of soil in contact with a layer of HCO3−-saturated exchange resin. The model parameter values were determined independently. The agreement between observed and predicted results was satisfactory given experimental limitations, indicating that the model correctly describes the important processes. A sensitivity analysis showed that all model parameters are important, indicating a simpler treatment would be inadequate. The sensitivity analysis showed that the amount of calcite precipitated and the spread of the precipitation zone were sensitive to parameters controlling rates of reactant transport (soil moisture content, salt content, pH, pH buffer power and CO2 pressure), as well as to the precipitation rate constant. We illustrate practical applications of the model with two examples: pH changes and CaCO3 precipitation in the soil around a plant root, and around a soil macro-pore containing a source of base such as urea.
Open Access
Soil microbial community assembly precedes vegetation development after drastic techniques to mitigate effects of nitrogen deposition
(Elsevier, 2016-10-03) van der Bij, A. U.; Pawlett, Mark; Harris, Jim A.; Ritz, K.; van Diggelen, Rudy
Oligotrophic semi-natural systems are threatened by high levels of nitrogen deposition. To mitigate these effects, drastic techniques such as sod-cutting and topsoil removal are applied to reduce nitrogen loads in existing systems and expand their area on former agricultural fields. We assessed the effects of these techniques along with the influence of previous land-use, isolation and vegetation development on subsequent microbial community assembly in restored agricultural areas. Microbial community phenotypic structure was measured using PLFA-analysis, along with soil chemistry and vegetation development. Differences in soil nitrogen pools due to restoration techniques were the most differentiating factor for both microbial community assembly and vegetation development. Only after topsoil removal was resemblance of both below- and above-ground communities to well-developed heathlands increased within 10–15 years. After sod-cutting both microbial community and vegetation composition remained more similar to agricultural sites. The relative contribution of agricultural sites and heathlands in the direct vicinity had more pronounced effects on local microbial community composition than current land-use in all study sites including agricultural areas and heathlands. Vegetation development was apparently of minor importance for microbial community assembly, since characteristic belowground assembly preceded that of aboveground development in both restoration contexts.