At doses exceeding those used in agriculture, Carbyne and its constituents of formulation, barban and solvents, exert several effects on the activity of soil micro-organisms. Soil respiration was initially stimulated by addition of all the formulation components. In the case of solvent and Carbyne applications, the stimulated respiration was accompanied by a rise in the bacterial population in response to the additional carbon in the solvent. In contrast, there was no initial increase in microbial population in barban-treated soil. Carbyne, and to a less extent barban, inhibited respiration in soil during later stages of incubation (up to 220 days) although bacterial numbers present were considerably higher than in untreated soil. As barban and Carbyne treatment also depressed the rate of glucose utilization and increased phosphatase levels in soil, it is suggested that the active ingredient (barban) interferes with respiratory processes of soil micro-organisms. Nitrification in soil was inhibited for at least 18 weeks following treatment with barban and Carbyne, during which time neither Nitrosomonas nor Nitrobacter could be detected. Periodic introduction of fresh soil failed to re-establish nitrification. Solvent caused only a temporary inhibition of nitrification during the first two weeks. Using a multipoint inoculation technique, physiological tests revealed that treatments had a selective action on soil bacteria. This upset the balance of populations in soil, which failed to return to the control state for a considerable period. Carbyne treatment reduced numbers and types of fungi in soil. Some of the microbial effects of barban (nitrification inhibition and phosphatase stimulation) were shown to be partly attributable to 3-chloroaniline, a metabolite of barban detected in soil treated with barban and Carbyne. However, the metabolite did not cause the effects to persist nor did it inhibit glucose utilization. The presence of barban, either alone or in combination with solvent as Carbyne, appeared essential for the full and prolonged expression of all the observed effects.

Volume change and shear strength characteristics of compacted soil sample o have been investigated in terms of effective stresses. The behaviour of the soil in a partly saturated state has been compared with its behaviour in a saturated state. If the principle of effective stress is to apply to both states the components of the effective stress equation governing the behaviour of the soils should be obtainable by a direct comparison of results. Experimental evidence is given which indicates that the parameter X implicit in the effective stress equation for the partly saturated state, cannot be readily obtained particularly for volt change. This has been attributed to the dominating influence of structural effects, Using experimental evidence and an idealized model it is anticipated that a realistic ©caparison of toot results can be made if the structural effects can be minimised. In order to achieve this the requirement of similar saturation history Load have to be satisfied. The effect of air on permeability and consolidation lo discussed briefly and supported by experimental results. Equations are presented which demonstrate the effect of departures from the simplifying assumptions of classical consolidation theory. The practical implications of test data are reviewed with particular reference to their application in the construction and operation of earth embankments. The interpretation o± field pore pressure measurements in also discussed.

Using the tracer caesium-137 (137Cs) and experimental approaches this study quantified soil redistribution induced spatial variation of nutrients and soil organic carbon (SOC), net C flux between soil and atmosphere and soil respiration rate at various landscapes positions (eroding to deposition) within agricultural fields from the foot hills of Indian Himalaya. The depth distributions of 137Cs and the spatial patterns of 137Cs inventories were consistent with previous applications of the approach in that low inventories were associated with low concentrations in the cultivation layer and high inventories were reflected in deeper 137Cs profiles indicative of accumulation of labelled soil. This supports the contention that 137Cs is a suitable tracer for use in this environment. The study found that soil redistribution within fields altered the spatial variation of nutrients and SOC; with significantly lower concentrations of nutrients in the most eroded part of fields (upslope) and significantly higher concentrations of nutrients and SOC in the depositional part of field (downslope). The spatial pattern of nutrients and SOC is reflected in differences in depth distributions between eroded and depositional areas. The 137Cs and SOC inventory and depth distribution data were used to derive retrospective assessments of net C exchange between soil and atmosphere. The C flux quantification model was used to estimate lateral and vertical soil and SOC redistribution under an assumption of equilibrium conditions and the net exchange of C between soil and atmosphere was derived from the difference between measured and ‘equilibrium’ SOC inventories. Fluxes were derived for each landscape position within the agricultural fields studies and calculated at field and site scale. High rates of soil loss were measured and the results showed that the majority of eroded sediment and SOC was exported from field with only a small fraction redeposited within the field. The effect of soil and SOC redistribution was to create disequilibrium in SOC dynamics at eroding and deposition positions and this supported the formation of a field scale C sink. The sink strength is highest in the most eroded parts of the fields due to dynamic replacement of eroded C. This is assumed to be due to the high rate of incorporation of SOC-poor subsoil, with a large C-unsaturated surface area, into the cultivation layer. The C sink is smaller that those reported from high nutrient-input mechanised farm lands. Irrespective of the fate of exported SOC, the SOC stocks in the fields appear to be in dynamic equilibrium and, therefore, there is no evidence of a C source to the atmosphere due to erosion. Also the rate of SOC export from the fields is very high, especially when compared with mechanised fields and, if it is assumed that some portion of exported C is stored in some part of low lying area, the C sink strength would be comparable to mechanised farm lands. The soil redistribution and C flux study confirmed the existence of spatial variation in C flux at various landscapes position and was consistent with an important role for vertical mixing of soil and SOC in determining net C exchange with the atmosphere. This informed the design of the final element of the research that examined soil respiration differences in soil from shallow and deep layers in eroding and aggrading landscapes position. Respiration was measured over a one year period in samples derived from separate depth layers and in mixtures of soil from different depths at each landscape position. No significant difference was found in C release rate (per unit mass of C) from topsoil of eroding and deposition position but the subsoil of eroding pits exhibited significantly higher C release than the subsoil from deposition positions. This result suggests that topsoil in both locations has almost equal and similar C origin. The relatively high rate of respiration in sub soils from eroding pits may be due to the presence of a larger proportion of SOC formed from recently incorporated plant material (crop roots) at these locations. In buried and deposition locations the reduced mineralisation is consistent with the proposition that burial of top soil can contribute to formation of a C sink. In the samples containing mixed topsoil and subsoil, evidence for priming was seen where the respiration rate in the mixed sample was significantly higher than the expected rate based on the respiration rate seen in the separate depth samples. No priming was evident in mixed soils from eroding locations, suggesting that mixing of subsoil and surface soil does not accelerate loss of old SOC from the subsoil. In contrast, significant priming action was evident in mixed soils from aggrading locations suggesting that buried SOC at depositional locations may be subject to accelerated respiration as long as it is exposed to fresh plant input (as found in surface soils). In conclusion, despite the low input and low productivity of the farmlands in the Indian Himalaya region studied here, there is consistent evidence that high rates of soil erosion and soil redistribution have induced spatial variation of nutrients and SOC, net C flux and soil respiration rates that combine to create a pattern of SOC stocks that are close to equilibrium and, if some of the exported C is sequestered, to create a net C sink. This result again confirms that erosion induced redistribution of C does not directly cause a net release of C to the atmosphere. The consistency of these results with previous studies suggests that there is both scope and need for soil erosion induced carbon fluxes to be incorporated into carbon budgets, research frameworks, land management and climate change mitigation strategies at policy-relevant scales.

The application of fertilisers has greatly increased agricultural yields. However, it has also had wide ranging consequences for ecosystem properties and processes, generating concern over the long-term sustainability of fertiliser management. Despite this, there is considerable uncertainty regarding the long-term impacts of fertilisation, especially on soil carbon, and this is largely due to the paucity of published findings from long-term experiments. In this project very long-term field experiments and a short-term microcosm trial were used to investigate the effects of fertilisation on agroecosystem properties with a particular focus on soil carbon dynamics. The effects of long-term fertiliser addition on key ecosystem properties in the Palace Leas Hay Meadow Experiment was determined and compared with those observed at other long-term and with short-term experiments. Farmyard manure addition was found to have many benefits over the use of inorganic fertilisers for improving agricultural production including higher nutrient availability, hay yields and the prevention of soil acidification. The magnitude of short- and long-term effects of fertilisation differed markedly, underlining the value of using long-term experiments to realise the true ecosystem response. The relative importance of three major classes of fertiliser-mediated mechanism was also evaluated using structural equation modelling and a complementary ley-arable rotation experiment. These studies found that soil C dynamics were altered by both direct (nutrient) and indirect (plant community- and soil pH-change) effects of fertilisation. Soil pH was the primary regulator of the microbial response to fertilisation, with soil acidification effects strongly negatively affecting microbial functioning when it reduced soil pH below 5. A microcosm study indicated that these effects of acidification on the microbial community cannot easily be reversed. As microorganisms regulate biogeochemical cycles which are critical for food production, fertiliser-induced acidification could therefore hinder long-term agricultural sustainability. Accordingly, soil pH in fertilised systems must be managed vigilantly.

No description available.

Reinforcement of soil by fibrous roots is crucial for preventing soil erosion and degradation,yet the underlying mechanisms are poorly understood. Without fully understanding root enmeshment within the soil matrix, and root biomechanical properties key for increasing soil shear strength, adoption in main stream civil engineering, understanding of natural systems and implications to agricultural soil management will be limited. Within this thesis theunderlying processes that drive root reinforcement of soils were assessed through a variety oflaboratory and field based experiments. This included recent advances in geotechnical engineering and model plant lines with specific root traits. Plant lines were barley (Hordeum vulgare) from a mapping population where differences in root hairs, tortuosity and lignin biosynthesis were previously identified by screening large numbers of mutants.The initial hypothesis was that root numbers and area would control shear reinforcement, this was tested by altering planting density in both glasshouse and field experiments using one barley variety. After 5 weeks in the field, planting density was related to both reinforcement and root area ratio (RAR), with a 6.7 ?1.40 kPa, or 190%, increase in shear strength between 0 and 950/m2. By 20 weeks in the field shear strength increased by only 29%. The glasshouse study showed an increase of 53%, with a positive correlation to planting density.Relationships between root number and shear strength were not explicit, however, highlighting further possible interactions between soil shear strength and root inclusions. Various underlying processes were then investigated. Barley mutants, with differences in root hairs and tortuosity, were compared to parent lines. Hairless mutants had different root tensile strength characteristics, but experimental difficulties (malfunctioning logging hardware) prohibited detection of impacts on shear strength. A refined study was then performed that also incorporated the influence of abiotic stress from compaction and waterlogging. Barley with down-regulated lignin biosynthesis (Bowman 140) had increased nodalroot tensile strength of 37% compared to the parent line (Bowman Line) under good growth conditions, but this changed to -31% for compacted and 26% for water-logged soil. In addition to abiotic stress, the age of the roots (measured as distance from root tip) type of root (seminal, nodal or lateral) had a large impact on biomechanical behaviour.

No description available.

No description available.

Three new large British centrifuges have been constructed in recent years for the purpose of testing soil models. A centrifugal model, in which the stresses are brought into similarity with those in a prototype by increasing the self-weight of the soil, can be used either as a means of providing data against which analyses may be checked or as an analogue to solve difficult boundary value problems for which no satisfactory analysis exists. Both uses contribute to the progress of soil mechanics as a science and to its application in engineering design. This thesis describes the use of one of the new centrifuges to investigate a design problem: the stability of floodbanks in the Thames estuary when they are subjected to abnormally high tidal conditions and associated uplift pressures in a permeable layer beneath the marsh on which they are built. The objective of the investigation was defined in general terms so as to allow the use of soils prepared in the laboratory in the first series of model tests, described here; a second series of model tests utilising prototype soil samples was envisaged but has not yet been carried out. Conventional laboratory tests were performed on the soils chosen fox the investigation in order to provide information which could be put to use in building the models and in analysing the results of the model tests. The interpretation of the laboratory tests proved more difficult than anticipated because of the need to define undrained strength relationships for two different clay soils taking into account, for one of them, experimental evidence of anisotropy. Whilst neither the soil conditions nor the loading conditions of the prototype could be closely simulated, it was deemed necessary to first bring the soils in the model into a state of equilibrium, by consolidating them in the centrifuge, and then to subject them to a rapid change of loading consisting of an increase of self-weight or an increase of uplift pressure or a combination of the two. Before the tests could be carried out, a means of controlling water movement in the model had to be developed. Substantial data of pore pressure and settlement during consolidation are presented which show that a state of equilibrium was indeed reached by the model soils. The rapid changes of loading generated two types of failure: failure of the embankment by slipping and failure of the marsh on the landward side of the embankment by bursting; these events occurred independently in the model so that the presence of even-very nigh uplift pressures did not influence the stability of the embankment. The results are expressed in the form of an interaction diagram. The tests have been interpreted by extending the model behaviour qualitatively to the prototype, which must be done with caution, and by comparing the embankment failures with the predictions of stability analyses previously used in design. Despite uncertainties, which are discussed, reasonable predictions. of model behaviour are obtained in the absence of high uplift pressures; in the presence of high uplift pressures previous design assumptions appear over-conservative but may not be should bursting of the marsh occur near the toe of the prototype embankment. In conclusion some statements relating to the stability of the prototype embankments are made, some limitations of centrifugal modelling are pointed out and some views concerning the role of the centrifuge in British design practice are expressed.

This thesis investigated the fate of organic contaminants (naphthalene, phenanthrene and azoxystrobin) in soils amended with biochar. This research considered both microbial biodegradability and chemical extractability. In order to assess the risk posed by organic contaminants in soils, knowledge of the bioavailable and bioaccessible fractions of the organic contaminants are of prime importance rather than the total concentrations. The bioavailable and bioaccessible fractions were defined and determined using respirometry assay and chemical extractions using methanol, calcium chloride (CaCl2) and hydroxypropyl-~ - cyclodextrin (HPCD). In different experiments, biochar was amended in soils at varying doses, particle size and types. The findings of this thesis illustrated that the rates and extents of mineralisation of 14C_PAHs and 14C-azoxystrobincan be controlled by application of biochar varying in dose and type. Furthermore, this study validated the HPCD extraction technique in predicting the bioaccessible fraction of PAHs and azoxystrobin in soil. Results indicated that the presence of biochar in soil reduced the bioaccessibility but did not alter the ability to estimate bioaccessible fractions. This was shown by linear correlations between extents of mineralisation and HPCD single extractions of PAHs in soils. Notably, the presence of biochar in the soils enhanced sorption of contaminants to reduce bioaccessibility but did not inhibit catabolic activities of indigenous microorganisms. The ability of biochar to control bioaccessibility of organic contaminants in soils could be related to difference in biochar intrinsic properties that were determined using nuclear magnetic resonance cryoporometry.