Browsing by Author "Leeds-Harrison, Peter B."
Now showing 1 - 12 of 12
Results Per Page
Sort Options
Item Open Access Effect of root activity on soil hydraulic properties(Cranfield University, 2003-01-28) Riseley, B. A.; Leeds-Harrison, Peter B.; Whalley, W. R.As plant roots grow through the soil, the hydraulic properties of the adjacent soil may change and be altered through the release of exudates and mucilage or through the re- arrangement of soil particles. Though these two possible mechanisms have been identified in the literature, the published work has not distinguished whether the change in water release and sorption are due to the mucilage affecting surface tension and/or contact angle or if the growing root re-arranges the soil particles so that there is less pore space that can hold water. In this thesis the effect of mucilage and particle re-arrangement on rate of inltration and water release has been studied. First, the effect of mucilage and particle re-arrangement on rate of inltration of water was investigated. Wheat, maize and barley plants were grown in silty loam cores. The results illustrated significant differences between these plant species grown in the soil cores. More importantly when maize seedlings were grown in sandy soil rhizoboxes the rhizosphere and bulk soil were significantly different, with the sorption rate being greater for the bulk soil. To explain these differences the impact of both soil density changes and mucilage on inltration in soil were studied. The lower density was significantly different compared with the higher density, with the lower having a greater sorption rate. There was no effect of mucilage on inltration but there were significant differences between the sorption rate at different time intervals. The effect of mucilage and particle re-arrangement on water release was investigated using rhizosphere and bulk aggregates and soil from plastic rings. The water content of rhizosphere soil was not significantly different from that for the bulk soil at saturation, suggesting that roots had no effect on the porosity of the soil. However the water content of the rhizosphere soil for maize and barley was significantly lower (P<0.05) at a pore water pressure of -0.15 kPa. The capillary fringe in glass capillaries using deionised water and natural mucilage was measured and it was found that mucilage decreased the capillary fringe to 0.7 of that for pure water. However application of this value to the bulk soil water release characteristic did not account for the changes observed in the water release characteristic for the rhizosphere soil. Possible explanations for the results from the sorption and water release experiments include wetting and drying, change in contact angle and surface tension by mucilage, particle re-arrangement increasing soil density, and microbes altering mucilage concentrations. It is concluded that the re-arrangement of soil particles by roots was found to be more important than the changes caused by the release of mucilage in affecting the hydraulic properties of the soil.Item Open Access Future irrigation water demand and on-farm water conservation in England(Cranfield University, 2001-02) Weatherhead, E. K.; Leeds-Harrison, Peter B.The aim of this thesis is to predict the future demand for water for irrigation of outdoor agricultural crops in England, and to assess the likely on-farm responses to potential water shortages and related legislative change. The past underlying growth in the demand for irrigation water was assessed, by regression analyses of the MAFF irrigation survey results, for each of eight crop categories and in total, using modelled irrigation need as a proxy for climate variation. The growth in total water demand was validated by comparison with the reported growth in total abstractions. These indicate an underlying growth in total irrigation water use between 1982 and 1995 of between 3% and 4% per annum, expressed as percentages of the 1995 values. The results show that irrigation has been increasingly concentrated on the more valuable crops, notably maincrop potatoes, small fruit and vegetables, and that those crops that are irrigated have been increasingly given more water. The future growth in the demand for irrigation water, for each of the eight crop categories and- in total, was modelled as the product of predicted future crop areas, proportions to be irrigated, depths of water to be applied and application efficiencies. On-farm economic modelling, macro-economic models, and expert opinion were used to predict future changes in each of these factors. A spreadsheet model was then used to calculate the future growth in irrigation water demand, for each crop category and in total, and for each Region and nationally. The same methodology has also been applied within a GIS to map the spatial variation in growth. In later work, the Foresight scenario approach has been used to consider alternative socio- economic futures. These results predict that in the short to medium term at least, the total demand for irrigation water will continue to grow rapidly, and its use will become even more concentrated on the high-value crops. Growth is greatest in those areas where water resources are already most scarce. Meanwhile, water availability for agriculture is expected to be constrained or even decline because of increased environmental protection, particularly in the drier parts of the country where irrigation is concentrated. Climate change has not been modelled in this work, but under current predictions, it is likely to have a double effect, simultaneously reducing water supply and increasing water demand, and hence increasing the scarcity and value of water and the benefits of water conservation. The farmers' likely responses to the almost inevitable water shortages have been assessed by estimating the net on-farm value of the water, and comparing this to the benefits and costs of the various options for either reducing demand or increasing on-farm supply, within likely technical, legal and other constraints. The aspects considered include irrigation methods, scheduling, agronomic practices, mulches, on-farm reservoirs, water harvesting and water re- use. This analysis shows that the on-farm benefits of irrigation are generally substantially higher than the direct costs of irrigation. The benefits of conserving water are highly variable, partly because inflexible licensing restricts opportunities to reallocate water between farms. The thesis shows that on those farms where water is valuable and scarce, this will lead to on-farm investment particularly in on-farm reservoirs, more advanced technology and better scheduling. Constraints to change are discussed. Meanwhile, on farms which already have adequate water resources, there is at present little financial incentive to adopt any irrigation water conservation measures at all. The thesis concludes that both farmers and water regulators must prepare for a less certain future in which water for irrigation is scarcer and more valuable, and demand is higher and more concentrated. The opportunities for action by various groups are discussed.Item Open Access Integrated washland management for flood defence and biodiversity(2004-01-01T00:00:00Z) Morris, Joe; Hess, Tim M.; Gowing, D. J.; Leeds-Harrison, Peter B.; Bannister, N.; Wade, M.; Vivash, R. M.In the context of growing interest in finding sustainable solutions to flood management in England and Wales, this study set out to determine the extent to which benefits to flood management and biodiversity can be achieved through an integrated approach to the creation and management of ‘washlands’. For the purpose of the study, a washland is defined as “an area of the floodplain that is allowed to flood or is deliberately flooded by a river or stream for flood management purposes, with potential to form a wetland habitat”. Following a questionnaire survey of engineers and conservationists, a review of selected sites, and a workshop of key stakeholders, it was concluded that there is both scope and willingness to exploit potential synergy. It appears, however, that until now most washlands have either been used mainly for flood storage or for wetland habitat, and there has been only a limited attempt to integrate the two objectives. In many respects, the opportunity for integrating biodiversity depends on the ability to maintain wet conditions on the washland beyond the period of the flood event, and this largely depends on the dominant land use. The scope is greatest where the washland is under grass or woodland, and actions can be taken to ‘engineer’ or manage soil wetness regimes which serve biodiversity interests. Such water management plans and related biodiversity targets are best designed into washland management from the outset, rather than as an afterthought, when conflicts of interest are likely to arise. While there is much interest in pursuing an integrated approach, lack of funding for biodiversity on washlands and the relative complexity of preparing the washland case for appraisal appear to constrain washland development. Nevertheless, washlands are perceived by engineers and conservationists alike to offer potentially sustainable solutions to flooding, enabling biodiversity targets to be met within an integrated approach to catchment flood management. Recommendations were made to: • improve, through the use of guidance and training, understanding between engineers and conservationists of how flood management and biodiversity objectives can be simultaneously achieved; • consider the establishment of a biodiversity fund to support the biodiversity components of washland schemes; • develop practical guidance on the formulation of washland management plans that exploit biodiversity potential by managing wetness conditions in washlands beyond the flood-event period; • review how washland creation and management can be integrated and help to deliver the objectives of Biodiversity Action Plans and Catchment FloItem Open Access Integrated washland management for flood defence and biodiversity(2003-01-01T00:00:00Z) Morris, Joe; Hess, Tim M.; Gowing, D. J.; Leeds-Harrison, Peter B.; Bannister, N.; Vivash, R. M.; Wade, M.A combination of reform of agricultural policy, changing priorities in the countryside, growing commitment to protect and enhance biodiversity, and concerns about increased flood risk in lowlands have drawn attention to the potential contribution that managed washlands can make to deliver benefits to biodiversity and flood management. In this context, and with funding from Defra and English Nature, the study reported here1 set out to determine the scope for simultaneously achieving flood management and biodiversity objectives, and how this might be achieved in practice. The broad purpose is to inform policy on washland creation and management, including mechanisms for implementation if deemed appropriate.Item Open Access Integrating flood management and agri-environment through washland creation in the UK.(2004-01-01T00:00:00Z) Morris, Joe; Bailey, A. P.; Alsop, D.; Vivash, R. M.; Lawson, C. S.; Leeds-Harrison, Peter B.In many river floodplains in the UK there has been a long history of flood defence, land reclamation and water regime management for farming. In recent years, changing policies with respect to farming, environment and flood management are encouraging a re-appraisal of land use in rural areas. In particular, there is scope to develop, through the use of appropriate promotional mechanisms, washland areas which will simultaneously accommodate winter inundation, support extensive farming methods, deliver environmental benefits, and do this in a way which can underpin the rural economy. This paper explores the feasibility of flood storage and washland creation, the likely economic impacts (on the agricultural sector) of this type of development, and the financial and institutional mechanisms required to achieve implementation. The outcome is the identification and assessment of a washland package within the UK agri-environment framework. However, given the diversity of circumstance and practice, it is suggested that a range of options, and not just those associated with management agreements and annual payments, is used for the management and administration of washland areas.Item Open Access Linking soil moisture status of winter sports pitches to measures of playing quality(Cranfield University, 2005-12) Jennings-Temple, Marke; Leeds-Harrison, Peter B.A review of traction and hardness Performance Quality Standard tests highlighted significant relationships with soil and grass factors. Inadequate guidance to achieve test results through pitch management means that management practices can not focus on injury prevention or playing quality. A clear link between factors that can be managed by Groundsmen and the traction and hardness tests is required. The concept of effective stress significantly linked moisture status to soil strength in the laboratory. Penetration resistance was shown to be complex and affected by grass roots and bulk density, which prevented a single model encompassing all soil types to be established. Prediction of traction and hardness used grass and soil factors and varied according to soil type and wet or dry test conditions. In situ tests showed no variation due to pitch test position and as sand content increased, prediction became less reliable. A decision support model used the regression results to provide Groundsmen with the ability to monitor pitch quality in real-time. Effective stress successfully linked moisture status and strength although in situ verification is required. Regression analysis and the decision support model will assist Groundsmen in managing pitches while targeting playing quality. Further research to understand how management practices impact on quality and to understand the link between injury rates and type, and the results of traction and hardness tests is required. This knowledge will enable a company to simultaneously differentiate itself from competition and create a barrier to potential entrants.Item Open Access Low-lying agricultural peatland sustainability under managed water regimes(Cranfield University, 2006-05) Dawson, Quentin L.; Leeds-Harrison, Peter B.; Burton, R. G. O.The combined effects of ditchwater management regime and sub-irrigation spacing on water table fluctuation have been investigated for two low lying agricultural peatlands in England, West Sedgemoor in the Somerset Moors and Methwold Fen in the Norfolk Fenlands. The consequence of the resulting soil moisture regimes for microbially mediated mineralisation of soil organic matter has been examined on peat samples collected from the upper metre of peat profile from these two test sites. It is shown that sub-surface tile spacing has a strong influence on the transference of ditchwater regime to the mid-tile point in the field. Where sub-irrigation spacing is greater than 40 m the mid-point water table falls to similar levels experienced without any form of sub-irrigation intervention. Where sub-irrigation is at 10 m intervals the mid-point water table was found to be close to the water regime maintained in the ditches. Differences in field water-table level can lead to considerable variation in the matric potential experienced at different depths in the peat profile. As a consequence, peats at different stages of degradation (linked to depth) and under different land uses can exhibit variable physical and hydraulic properties. The von Post scale, which describes the degradation status of peats, has been linked to these physical properties but no simple model has been found between these properties and the von Post score. A good relationship has been found between saturated hydraulic conductivity and the van Genuchten alpha value which itself was related to the air entry value for all peats except the amorphous (unstructured) peat from Methwold fen. The water management regime, in conjunction with variations in physical and hydraulic properties of different peat types, influences the peat microbial community structure. At West Sedgemoor those peats that are wetter have predominantly anaerobic species, whilst those in drier environments have a greater proportion of aerobic species. At Methwold Fen the variable nature of the water management strategy appears to have homogenised the microbial community throughout the entire peat profile, resulting in more aerobic microbes in the deeper peat deposits. The type of microbial community and the degree of peat aeration dictate the efficiency with which soil organic matter is mineralised. Over the period October 2004 - July 2005 the rate of mineralisation in Methwold Fen peat samples averaged 0.40 g CO2-C m-2 hr-1 in saturated samples whilst in drier peat it averaged 0.72 g CO2-C m-2 hr-1. This clearly demonstrates that a wetter peat profile minimises the rate of microbially mediated organic matter mineralisation. Land use exerts an equally strong influence on microbial activity and can mask the true extent of soil organic matter mineralisation. Root exudates may offer an alternative source of organic carbon for microbial metabolic processes. Where the water table was maintained at 0.3 m below the soil surface respiration rates on grass covered West Sedgemoor peat samples was, at maximum, 1.46 g CO2-C m-2 hr-1 whilst on bare Methwold Fen peat samples it was less, at 1.06 g CO2-C m-2 hr-1. After removal of all surface vegetation the average rate of respiration switched, with Methwold Fen peats exhibiting a greater rate of organic matter mineralisation (7.27 µg CO2-C g soil-1 hr-1) than West Sedgemoor peats (3.8 µg CO2-C g soil-1 hr-1). Sub-irrigation modelling, using a drainage theory based water table model, can adequately simulate the soil water balance. Coupling the output of a comparable hydrological model (SWAP) with a process based model of nutrient dynamics(ANIMO) demonstrates that under future climate scenarios closely spaced subirrigation could reduce the mineralisation of soil organic matter to the atmosphere and reduce subsidence by up to 2mm year-1, thus reducing agricultural peatland contributions to greenhouse gas emissions and improving peatland sustainability1. Even partial aeration of a moist soil profile can lead to high rates of mineralisation. However, a combination of ditchwater management and sub-irrigation can, improve the sustainability of low lying peatlands if the management regime maximises the period of complete peatland inundation. 1 Sustainability being defined as maintenance and/or improvement of peat soil resource quality and/or longevity through the reduction of present day rates of subsidence and mineralisation.Item Open Access Nitrogen mineralisation and leaching losses from farm-yard manure under simulated centre pivot irrigation(1997) Almadini, Addukrahman Mohammad; Leeds-Harrison, Peter B.Nitrogen (N) leaching losses resulting from agricultural activity are a major concern to researchers and land managers in different parts of the world, due to the adverse effects of dissolved nitrogen on the water environment and on farmers’ returns. In this study the effects of intermittent irrigation, such as that occurring under centre pivot irrigation, on leaching losses of nitrogen mineralised by micro-organisms from different application rates of farm-yard manure (from 0 to 80 t FYM ha¯¹) and N fertiliser (300 kg N ha¯¹) mixed with sand have been examined using pots and leaching columns. Different N species (Ammonium, NH₄ᶧ-N; nitrate, NO₃¯-N; and total soluble nitrogen, TSN) have been investigated in the effluent samples collected from the bottoms of the pots and columns. Initially, in the pot experiments the results showed that there were significant differences (P = 5%) between the amounts of nitrogen mineralised from the different FYM application rates under different wetting treatments. The moisture conditions had greater effects on nitrogen mineralisation than FYM application rates. However, the opposite was observed when the C:N ratio of the applied FYM was narrowed by the addition of urea as a N fertiliser. Nitrification did not occur in a mixture of FYM- sand (i.e., un-modified sand), which was attributed to the lack of nitrifying bacteria in the mixture. However, inoculating the mixture with a sandy loam field soil caused NO₃¯-N to be the major N species in the effluent samples. In the leaching columns,NO₃¯-N was the dominant nitrogen form found in the effluent. NO₃¯-N concentration was significantly affected by the irrigation practices. The highest concentration (95 mg NO₃¯-N ɭ¯¹) has been found for the treatment in which the top sections containing the applied FYM have been maintained at the field capacity moisture condition. A relationship between the frequency of water application and NO₃¯-N movement in the soil columns was found. The amount of NO₃¯-N leached from the soil columns wetted every four days > eight days > twelve days. This suggests that frequent irrigation practices leach NO₃¯-N further in the soil profile increasing the possibility of NO₃¯-N leaching beyond the root zone. In addition to water application practices, the start of NO₃¯-N breakthrough was related to the moisture conditions of the soil columns. For the soil columns maintained continuously at the field capacity, 812 ml cumulative effluent was needed before the NO₃¯-N breakthrough, compared to 610, 464, and 381 ml which were needed for the soil columns intermittently wetted for 4, 8, and 12 days, respectively. This indicates that more water is needed before NO₃¯-N breakthrough under wet conditions than under dry conditions. The amounts of N leached from the soil columns were correlated with the ratio of effluent to water applied, suggesting that irrigation and drainage practices have an impact on NO₃¯-N leaching losses. This study has demonstrated that there are relationships between the frequency of irrigation and N mineralisation and leaching losses from the applied FYM, which lead to the conclusion that minimum NO₃¯-N leaching losses are likely to be obtained under irrigated, fields when adequate adjustments for the nitrogen mineralised from the applied FYM are made and proper irrigation scheduling is practiced. The best management of nitrogen, which aims to maximise crop yields and minimise environmental impact, is proposed for centre pivot irrigation in the Kingdom of Saudi Arabia.Item Open Access Removal of ammoniacal nitrogen from landfill leachate by irrigation onto vegetated treatment planes(Elsevier, 2002-01) Tyrrel, Sean F.; Leeds-Harrison, Peter B.; Harrison, K. S.Leachate is a contaminated liquor resulting from the disposal of solid and liquid wastes at landfill sites that must be treated before discharge. Vegetated leachate treatment planes have been used at landfill sites in the UK but have received little scientific attention. This paper describes studies of model leachate treatment planes with a focus on the removal of ammoniacal nitrogen (NH3-N). Small-scale and field-scale experimental treatment planes were constructed, filled with clay loam soil and vegetated with grass (Agrostis stolonifera). Landfill leachate was applied at hydraulic loading rates ranging from 17-217 l/m2/d. An exponential relationship was used to characterise the pattern of NH3-N removal. No relationship was observed between the hydraulic loading rate and the NH3-N removal rate constants (R2 = 0.0039). The daily specific NH3 -N mass removal rate was found to be linearly related to the NH3 -N concentration at the start of that day of treatment (R2 = 0.35). Possible causes of variation in the rate of NH3-N removal between experiments are discussed. A simple inorganic nitrogen balance indicated that the mass of NH3-N and NO2-N removed was not accounted for by NO3-N production. Explanations for this apparent nitrogen deficit are discussed.Item Open Access Soil-based services in the built environment: A report prepared for the Department of Environment, Food and Rural Affairs(Cranfield University, National Soil Resources Institute, 2005-05) Wood, Gavin; Kibblewhite, Mark G.; Hannam, Jacqueline A.; Harris, Jim A.; Leeds-Harrison, Peter B.Background: Publication of the First Soil Action Plan for England in 2004 has drawn attention to the value that can be derived from the protection and appropriate management of the country’s soil resources. This principle applies all soils equally including those in built environments which are the subject of this report. Soil is valuable because it underpins both quality of life and biodiversity conservation. It does this by providing a range of services or functions which meet human needs and sustain natural systems. The principal of these are environmental regulation and environmental maintenance, food and fibre production, above and below ground habitat maintenance as support for biodiversity, protection of cultural services and provision of a platform for the built environment. Soil is, in practical terms, a non-renewable resource which can be destroyed by construction. To help protect soils in the built environment, the services they can and do provide to both society and the environment need to be documented and explained. This report proposes a framework to help explain soil’s services and functions within built environments and provides a literature-based review of those services, their current perceived value, and a risk assessment of the threats that may degrade them.Item Open Access Water quality from contrasting drained clay soils : the relative importance of sorbed and aqueous phase transport mechanisms(Cranfield University, 1997) Hardy, I. A. J.; Carter, David; Leeds-Harrison, Peter B.A full understanding of the processes controlling the movement of pesticides within the soil 1 water regime is critical to the successful reduction of losses of these substances to surface waters. Until recent years the importance of absorbed phase transport of pesticides has largely been ignored with respect to drainflow and the appearance of strongly absorbed hydrophobic compounds in riverine sediments has hitherto been largely attributed to surface runoff 1 erosion. Field studies were setup for the 1994/5 winter season to investigate the hydrology and chemistry associated with drainflow from the lighter clay soils of Boarded Barns Farm, with two calcareous (Hanslope and Stretham) and two non-calcareous (Melford and Ludford) soils being chosen for study. Instrumented study plot areas were established in each field, with drainflow measurement and water sampling being automated. Laboratory based investigations (including rainfall simulation and desorption) were carried out to support, extend and clarify the field data, in particular the processes involved in the transport of isoproturon and sediment. A striking feature seen in the field studies was the appearance of large amounts of suspended sediment in drainflow from the Melford soil, in contrast to the clear drainflow from the calcareous soils. The sediments in drain flow were identified as being of surface origin, generated by rainfall impact and transported via preferential by-pass flow. Laboratory investigations have indicated that the chemical nature of the topsoil is a dominant factor controlling the transport of sediments and clay flocculation due to the presence of calcium carbonate is proposed as a mechanism for preventing sediment transport in the calcareous soils. Where sediment was found in drainflow, it was shown to be responsible for the transport and losses in the absorbed phase of not only diflufenican, a strongly absorbed pesticide, but also isoproturon, a weakly absorbed pesticide. The laboratory studies indicate that isoproturon is transported predominantly absorbed to sediment and later desorbs 1 diffuses slowly into the aqueous phase of the receiving waters. The results of the field experiments were confirmed by the rainfall simulation studies on 20cm deep (20cm diameter) topsoil cores taken from the field, which showed sediment transport only in the non-calcareous soil. The extent of this phenomena of sediment transport in the UK is not well defined, due to the historical lack of research, however soils known to show the effect have a land coverage of 6% of England and Wales. The present study highlights an additional mechanism by which pesticide losses to surface waters may occur, but the relative importance will depend heavily on the hydrological, structural and chemical nature of the soil system.Item Open Access Water table control for rice production in Ghana(Cranfield University, 2005-09) Owusu-Sekyere, Joshua Danso; Leeds-Harrison, Peter B.An investigation has been undertaken to determine the consequence of using water table control for lowland rice production by growing rice varieties Azucena and IR36 in sand cores under a controlled environment in a series of experiments in which the water table was held at fixed levels. Each experiment had a duration of six weeks and in all, four treatments were used: (a) water table at a depth of 30 cm below the surface, (b) water table at a depth of 15 cm below the surface, (c) saturated sand and (c) flooded sand. Growth under the two water table depths compared favourably with the flooded and saturated conditions, with plants under the water table control treatments in some cases performing better in terms of plant performance than the saturated or flooded. Plant growth parameters measured were: Tiller number, root dry mass, shoot dry mass, rooting depth, total root length and plant height. Other parameters measured are: Solution nitrogen concentration, redox potential, growth medium temperature and pH levels. When IR36 was used the total root length, number of roots and tiller numbers were significantly greater for the plants in the saturated treatment but there were no significant differences in root mass, shoot mass, and shoot length with regards to water depth. When Azucena variety was used, the 15 cm treatment had the highest shoot mass in addition to the highest tiller numbers. In other parameters, the 15 cm treatment did not show a significant difference to the saturated treatment. The 30 cm treatment performed least well in all parameters measured. Plants under the flooded treatment had a significantly greater root dry mass, shoot dry mass and tiller number than the others. The plants grown under 15 cm water table depth had the least root mass. Tiller numbers for the plants under the 30 cm water table depth were greater than those under the 15 cm water table depth. Differences in plant development parameters generally appeared only after the fourth week. The data suggest that irrespective of the water treatment used, plant development trends remain the same indicating that in the first four weeks of rice growth much less water can be used without affecting plant development. Where Azucena and IR36 were both used the data suggest that water table control might be suitable for both varieties of rice. Differences in the amount of nitrogen present were seen to have had an impact on growth. Varying the form of nitrogen applied did not alter growth parameters to any appreciable extent implying that supply of nitrogen is more important than the form of nitrogen used. The effect of root properties and NH4+ transport through the soil on N uptake under different water regimes has been modelled. The model adequately predicted the root length densities required to explain N uptake rates. It is shown that root length densities increase with decreasing moisture content, allowing larger root length densities to compensate for low nutrient transport rates and although diffusion of nutrients increased with increasing moisture levels, nutrient uptake rates did not follow the same pattern. Rooting length densities and transport of nutrients are not shown to limit uptake of nutrients under any of the water treatments imposed. The feasibility of using water table control in the inland valleys of Ghana was also investigated by simulating the depth of the water table required in the dry season of the years 1996 and 1997. A comparison of water use under water table control and flooding irrigation showed that water savings were possible suggesting that water table control is feasible and beneficial in the inland valleys of Ghana.