Browsing by Author "Spoor, Gordon"
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Item Open Access The development of techniques of assessing soil compactability(1993-06) Earl, Richard; Spoor, GordonThe recent decline in farming profits has prompted an urgent need to increase efficiency, either by increasing outputs or reducing the cost of inputs. Soil compaction can influence adversely all stages of crop development, and hence yield, and is expensive to ameliorate in terms of time taken and power required. Minimum cultivation or direct drill crop establishment systems can reduce inputs, however, they are very susceptible to compaction from the previous season. There is a need to develop a greater understanding of the compactive nature of soil, and hence trafficability and workability, in relation to the selection of appropriate machinery to carry out agricultural operations. A study of research on soil compaction revealed that the majority of work to date has been carried out using disturbed soil samples in laboratory situations. The aim of this project is to develop techniques and models, based on field data, for assessing the susceptibility of soils to compaction by agricultural machinery. Work, conducted during this study, was carried out in the field in a range of soils, crops and climatic conditions. The study was approached by dividing the project into two sections:- (1) Prediction of trafficability and workability on a go/no-go basis. Soil water suction (h), soil moisture deficit (SMD) and cone penetration resistance were monitored at six field sites, under grass and an arable crop, covering a range of agricultural situations commonly found in central and eastern England. Strong correlations were found to occur between both h and SMD and:- (a) a qualitative assessment of soil condition, and (b) cone penetration resistance. These data formed the basis of models for predicting trafficability and workability at a given site on a particular day, and at any 5km square in England and Wales as an aid to business planning. (2) Assessment of the compactive nature of soil during loading. A methodology was developed which provides a measure of the susceptibility of soil to damage if land is trafficked when in an unsuitable condition. It is based on results of plate sinkage tests, in conjunction with those from confined compression tests, performed in the field using tractor-mounted equipment. Soil behaviour during compression was found to be governed by three phases:- (a) compaction with uniform lateral stress, (b) compaction with increasing lateral stress, and (c) displacement of soil laterally. Mathematical models are presented for predicting, for a given load and soil, the deformation phase and extent of disturbance likely to occur. The prediction models developed during this study provide a new approach to the selection of, and assessment of damage by, agricultural machinery.Item Open Access Feasibility of on-farm reduction of nitrate pollution in subsurface drainage water(1996-05-23) Hughes, Edmund John; Spoor, GordonNitrate polluted water from agricultural drainage systems is currently treated by the water industry for mains supply. Moves towards a polluter pays policy resulting from European Union legislation and consumer pressure will, however, have major implications for the agricultural industry. The aim of this study was to identify, investigate and evaluate on-farm strategies for reducing nitrate pollution in subsurface drainage water. The high peaked nitrate rich discharges of drainflows from agricultural catchments in late autumn present significant management problems. One possibility which was examined is for polluting drainflows to be identified, intercepted and diverted into a holding pond or reservoir. Once stored, possible effective handling strategies include: long term storage, dilution, recirculation of the polluted water back onto the .land, and anaerobic treatment. Anaerobic treatment is a method of reducing nitrate to harmless nitrogen gas, however, lower temperatures in late autumn would suppress microbial activity, and possibly treatment performance. Further detailed laboratory study was carried out to assess the potential of anaerobic treatment during winter. Initially, the hypothesis that the nitrate concentration of drainage water could be reduced when applied to soil was tested, leading to the conclusion that it was only possible when a readily utilisable carbon source was continuously present. Glucose was added to water with a nitrate concentration of 1 00mg/1 and applied to soil columns. Complete reduction of nitrate concentration was achieved at 10°C, demonstrating the feasibility of anaerobic treatment during winter. The study also confirmed the optimum application ratio of glucose-carbon to nitrate-nitrogen as 1.65 to 1, and the environmental threshold as a redox potential of 200m V. Attached growth water treatment systems which utilise soluble carbon sources are, however, unsustainable because clogging of the porous media by microbial biomass results in hydraulic failure. The hypothesis that organic materials be used both as carbon source and the microbial growth site was tested. Provisional examination of the biodegradability of several organic materials demonstrated that sugar beet could upon degradation be a source of readily utilisable carbon. Sugar beet was subsequently used in small-scale laboratory based nitrate reducing water treatment systems. An average treatment performance of 23 grams of nitrate-nitrogen reduced per cubic metre of bio-reactor per day was achieved by maintaining a near neutral pH environment with the addition of crushed limestone. Clogging was not experienced and therefore flow rate was both sustainable and controllable. An empirical based model was developed to predict the required flow rate of drainage water through the bio-reactor for a specified nitrate concentration reduction, ammonia concentration, and redox potential. Examination of drainflow data enabled polluting drainflow volumes and their associated average nitrate concentrations to be quantified, to form the basis of .a design specification for the proposed on-farm strategies. Designs for each strategy were made and limitations on use identified. Approximate costs were calculated and compared to the cost of on-farm anaerobic treatment utilising methanol as the carbon source. This demonstrated that treatment strategies offer a capital cost saving due to reduced design storage capacities, however, operating costs and the additional management expertise required make them less attractive to the farmer. Dilution has potential in areas where excess winter rainfall exceeds 200mm, however, the volume of water that can be diluted is limited. Recirculation requires further investigation, but has potential in areas of low excess winter rainfall and high soil moisture deficits, and where irrigation equipment is already available. Long term storage satisfies all the requirements for on-farm suitability, and would provide an additional environmental benefit of on-farm water conservation, at a cost 25% greater than that for off-farm water treatment alone.Item Open Access Interactions between tillage energy soil structural stability and organic matter(Cranfield University, 2003-11) Watts, Christopher W.; Godwin, R. J.; Spoor, Gordon; Whitmore, A.In agricultural production, disturbance of the soil by cultivation occurs regularly. Mechanical energy applied in this way can have a adverse effect on soil stability, a lowering of soil organic matter (S_OM), and a increase in CO2 emissions. These changes result in unwanted environmental consequences and compromise the ability of soil to maintain a competitive and sustainable agricultural industry. As agricultural systems evolve, it becomes important to develop a indication of their sustainability with regard to soil structure, well before any serious consequences become apparent. The am of this work was to quantify the effect of mechanical energy (in particular tillage) on soil structural stability and the loss of SOM. New laboratory techniques were devised in which mechanical energy was applied to a range of soils at different water contents with measurements made of stability and the mineralization of SOM. Techniques used for characterising stability involved measuring mechanically-dispersed clay, cm using a turbid metric technique and the proportion of water stable aggregates (>250 m). A re-examination of the statistical theory of brittle fracture showed that soil friability, F1, could be quantised using the coincident of Variation of tensile-strength of a population of similar sized aggregates. Specific energies associated with different cultivation practices, were simulated using a falling weight and results indicated that the sensitivity of soil to mechanical damage was essentially zero at soil water contents below the plastic limit (wpL). With increasing soil water content, sensitivity to destabilization increased sharply. The empirical model to characterise these phenomena was evaluated under field conditions where the energy consumption of different tillage implements, operating at different soil water contents, was measured directly. Good agreement between the level of destabilization measured in the field and those in the laboratory was obtained at similar specific energy values. C.W. Watts, 2003. Cranfield University, Silsoe. The field experiments also showed that increased levels of cm following tillage were responsible for stronger and less friable day aggregates. More experiments on a soil with SOC values ranging from all to 32 g/kg enabled the original model to be refined, linking cm, SOC and soil water content to disruptive energy. This led to the development of a index, S, which quantise the sensitivity of soil to destabilization by mechanical energy inputs and provides a method for identifying soils at risk. The effect of mechanical energy on the mineralization of SOC was measured using the falling-weight. Mineralization was characterised by measuring soil respiration using data-logging, conductinetric respirometers, built to monitor CO2 emissions following applications of mechanical energy. Changes in respiration were characterised by the respiration ratio, rr (defied a respiration following the application of energy divided by basal respiration). Higher values of, rr, were associated with greater energy levels, particularly on soils with lower SOC. Increased respiration was also measured following tillage in the field, particularly from soils following tillage at high energy levels where the effect lasted for several weeks. In this work three physically based measures of soil quality (S, F1 and rr) have been used to quantify the effects of tillage of different intensities on soil structural stability and the loss of organic matter. Parameters common to these measures of soil quality are SOC content, soil-water content and tillage intensity. Results of this work indicate that organic matter, physically protected by stable soil structures, can b exposed to mineralization when the structure in destabilized during tillage, particularly a the soil becomes wetter (w>w1ºL). The practical consequences of this work concluded that increasing the levels of SOC, cultivating the soil at water contents below the plastic limit and a reduced energy input, provide the best practical approach to maintaining soil physical quality. The new methodologies developed here have helped improve understanding of the effects of mechanical energy on soil structural condition. They provide a sound basis to answer a range of questions relating to soil physical quality and the consequences of different soil management practices for soil behaviour in the environment, thus enabling the boundaries between good and bad practices to b better defied.Item Open Access An investigation into wetland soil-implement mechanics(Cranfield University, 1990-06) Ahmad, Desa; Spoor, GordonAn investigation was initiated to obtain some understanding on the behaviour of soil at higher moisture content and to explore the potential of preparing paddy fields with reduced amounts of water. This investigation comprised of three separate studies. Based on existing information that water could be reduced when soil clods were initially formed prior to flooding, the effects of clod size, clod initial moisture content and confining states on the rate of water uptake were explored. The moisture gradients within clods wetted and dried for different period of times were also studied. The results of the clod wetting experiments show that· the rate of water uptake by capillarity was greatest when clods were initially very dry and smaller clods tended to absorb water faster than bigger clods when under confined conditions. Confining had no effect on infiltration when the initial condition was very wet. On drying, the smallest clod dried the fastest, reduced greater volume and increased its dry bulk density significantly. Larger clods required,longer drying period to arrive at a uniform moisture profile within as compared to smaller clods. Results from the wetting experiments were tested against the infiltration model of .Jarvis and Leeds-Harrison (1987) and a model developed based on linear flow of heat into a solid (Carslaw and Jaeger, 1959). A second project involved the study of soil deformation at high moisture contents in an attempt to produce clods with minimum draught force using simple relieved tines at various rake angles and depths in a soil tank. The principal. objective of the - ii - study was to utilise soil implement mechanics knowledge to improve the efficiency of soil preparation for wetland crops. Aspects like the nature of soil disturbance, extent of disturbance and draught requirement were investigated. The soil was in a plastic consistency prepared to three specified density states of 940, 1000 and 1250 kg/m3• The soil disturbance pattern was monitored using implanted coloured beads and glass sided tank studies. In addition, the extent and height of heave and surface disturbance were noted. Predictive models based upon Mohr-Coulomb soil mechanics theory were developed to predict the interaction between the soil and simple implements at three rake angles. These were based on the lateral failure theory of Godwin and Spoor (1977) and the two dimensional soil failure model of Hettiaratchi and Reece (1974). Results from the single tine study were tested against the models. A sliding resistance component and crescent effect were incorporated to improve the predictions for the 45° and 90° rake angle tines. The magnitude of each mode of failure is dependent upon the critical aspect ratio which varies with tine rake angles and soil conditions. The mode of failure is considered to be lateral when the tine aspect ratio is larger than the critical aspect ratio and an upward failure when the tine aspect ratio is lower than the critical aspect ratio. The predicted results are in close agreement with the results of the experimental studies. For the backward raked tine, a model was developed based on the formation of an elliptical wedge and bearing capacity type of failure ahead and below the wedge. This failure theory was based on the bearing capacity failure for deep footings. The model - iii - helped identify an additional parameter that influenced the draught force for a backward raked tine. This parameter is the sliding resistance component on both sides and beneath the elliptical soil wedge •. Results from multitine studies showed that draught force increased with tine spacinq but the increase was not significant. In the wet condition the tines merely cut slots and little or no interaction was noted. In an effort to find the optimum water level for soil puddlinq, a laboratory study was conducted to determine the influence of water-soil ratio on the ease of puddling air dry aqqreqates. Soil puddlinq was carried out usinq a·rotary stirrer simulatinq the rotary motion of a rotary cultivator commonly used in wetland preparation •. The results obtained showed that· the fastest dispersion of particles resultinq in a minimum wet bulk density of 1.23 Mg/m3, was achieved at a water-soil ratio of 1.2. (A supersaturated condition equivalent to a moisture content of 120% dry basis). Increasing the water-soil ratio above this value did not change the wet bulk density value for all stirring times.Item Open Access Reducing deep soil compaction through strain modification under different wheel arrangements(Cranfield University, 2002-02) Javadi, Arzhang; Spoor, GordonNew mechanisation methods associated with increasing loads have the potential to cause undesirable deep compaction, which is difficult, expensive and in some cases impossible to alleviate. Avoiding or reducing the risk of deep compaction seems to be the most straightforward solution to compaction management. Previous research indicates that some benefits can be achieved through interactions between cultivation tines or other implements, in terms of the magnitude of forces and the extent of soil deformation. Interaction within wheel arrangements could have benefits for reducing deep soil compaction. This study aimed to reduce the risk of deep soil deformation by locally modifying soil conditions through interactions in order to increase soil resistance and hence load support in the surface layers. To test the hypothesis, the research was based on soil mechanics theories and failure mechanisms related to bearing capacity in order to identify the major factors influencing load support and soil displacement. The nature of soil failure patterns, interaction behaviour, soil deformation and load/sinkage relationships were investigated under a wide range of dual and triple spaced footings/wheels configurations. Small-scale tests using rectangular plates were firstly conducted in a glass-sided tank. These initial tests were followed by larger-scale tests in a soil bin and in the field under different soil conditions using actual wheels, spaced and positioned as in the footing tests. The results indicate that it is possible to reduce soil displacement at depth by increasing load support in the soil surface layers through the interaction between spaced wheel arrangements. It was shown that different interaction modes occurred under dual configurations depending on the spacing between them. A locally compacted zone was created between the wheels under dense interaction conditions, increasing surface support. Surface support was increased further through a surcharging effect achieved by placing a third footing/wheel between and higher than the side wheels (triple arrangement). The central static interaction zone maximised the surface resistance locally under these configurations. Although single wide section wheels such as Terra tyres can tolerate higher loads at lower pressures, from a soil failure point of view, this is usually associated with large active and passive failure zones inducing deeper soil deformation. Triple spaced wheel arrangements with similar diameter wheels kept soil displacements shallower whilst carrying a similar load to a single very wide wheel with the same overall contact pressure. Reductions of up to 50% in the depth of soil displacement were achieved with the triple arrangements for the same load. These spaced arrangements can therefore be recommended as promising replacement for single wide wheel under heavy machinery application in practical situations. Benefits from the spaced arrangements are achieved in two ways: firstly by increasing surface support through creating locally compacted zones and secondly by reducing the size of active and passive failure zones causing shallower deformations. Stony soils provide more surface support than stoneless soils and also non-uniform soil with a denser layer at tillage depth can tolerate a greater load for a given sinkage compared with uniform homogenous soil. A mathematical model was developed to predict the vertical force under interacting shallow footings and showed an acceptable level of agreement with the experimental results. The model can be used to estimate the extent of the rupture distance of the side passive planes to assist in identifying appropriate spacings and interaction modes for spaced wheel arrangements.Item Open Access Soil Compactability(Cranfield University, 1985-08) Seig, D. A.; Spoor, GordonSubsoiling and deep loosening are widely used to alleviate soil compaction but little is known about the mechanics of the compaction process. Further information is required on the process that soil goes through during compaction, along with the effect on the amount of soil compaction of various tyre configurations. Such information will allow more confident recommendations to farmers on the suceptability of their soil to compaction. Experimental work was conducted where the soil deformtions of a light textured soil were monitored throughout the whole soil mass. The deformations in the soil were caused by a loaded pneumtic tyre on the surface. In the experimental work, both the process of soil compaction and the final state of the soil following the passage of a wheel were monitored. The experiments showed that soil compaction on light textured soils is caused by a punch failure of the soil, therefore most of the compaction is confined to the area directly below the wheel. The experimental monitoring of soil deformations was a slow and complex process, drawing firm conclusions from the work was further complicated by the interactions of the input variables, such as load and contact length. In order to monitor the effect of individual inputs on soil compaction a thre dimensional mathematical model of the process was developed from Theories of Elasticity and a confined compression soil test. The model predicted the subsurface deformations in the three principle directions due to surface loads. Once the model was modified to account for the support capability of the soil it proved it could, with resonable accuracy, predict the defomations and hence soil canpaction due to a tyre on the soil surface. The model was used to predict the effect of various tyre configurations on soil ccrnpaction. From a number of these runs it was possible to find the sensitivity of soil to compaction due to that input. The results showed that the sensitivity of soil to ccmpaction is not a linear relationship and significant reductions in the amount of soil, canpacted and the level of ihe compaction can be achieved by the right tyre configuration.Item Open Access Water management in deep peat soils in Malaysia(Cranfield University, 1992-03) Zakaria, Salmah.; Spoor, Gordon; Bakar, Zahari Abu; Welch, D. N.The study seeks to develop a field water management system for agriculture in peat soils in Malaysia, with an overall approach of integrating the engineering and agronomic aspects associated with crop production in deep peat areas. This includes the determination of soil physical parameters essential for field drainage design. The main experiments were carried out on a 10.9 hectare plot of land, initially drained 15 years earlier. The results were compared with data collected from a newly opened area and an area drained 40 years earlier. Cont/d.