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Title: Assessment of heavy farm traffic soil compaction using non-invasive and non-destructive techniques
Author: Shanahan, Peter William
Awarding Body: Lancaster University
Current Institution: Lancaster University
Date of Award: 2013
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Soil is a non-renewable natural resource at risk from degradation worldwide by human activities, mainly intensive agriculture. Soil erosion as a result of agriculture is a global problem, not only leading to loss of a growing medium, but increased pollution of fresh water systems. The soil losses from arable farmland by water erosion in excess of 1 ton ha-1 y(l has increased since the adoption of winter cereals in the UK, but exacerbated by soil compaction by heavy farm traffic. Heavy traffic impairs infiltration of rainfall, leading to infiltration excess overland flow, taking sediment and nutrients, namely phosphorus, off sloping arable fields. Tramlines, temporary lanes used for heavy farm traffic, effectively channel rainfall overland flow during the wet winters in the UK, focusing sediment and phosphorus transportation from arable land. This thesis covers the work carried out at Lancaster University from November 2009 to May 2012 in conjunction with a consortium of researchers and agricultural industry bodies, headed by ADAS UK Limited, to investigate cost-effective measures for reducing sediment and phosphorus losses from arable land. The full project: 'Reducing the risks associated with autumn wheeling of combinable crops to mitigate runoff and diffuse pollution: a field and catchment scale evaluation', was funded by the Sustainable Arable Link Project of the UK's Department for Environment, Food and Rural Affairs (DEFRA) through the Home Grown Cereals Authority. Field trials of low ground-pressure tyres compared to standard agricultural tyres, cropping within tramlines, and soil surface disruption were conducted over three growing seasons of winter wheat. The soil textures ranged from sandy loam to clays for three locations in England, and a sandy loam for one location in Scotland.1 This study focussed on investigating the physical parameters of the compaction caused by the heavy farm traffic and the effectiveness of low ground-pressure tyres in reducing soil compaction at the three field locations in England: Gatley in Herefordshire; Hattons in Staffordshire; and Loddington in Leicestershire. Tramlines, not monitored for overland runoff, but adjacent to those which were, was provided for this study. The soils of the tramlines, both wheeled and non-wheeled, were investigated with innovative approaches with radiographic, photographic and geophysical techniques to improve our understanding of physical changes to soil structure under heavy farm traffic. The aim of the study was to apply the above techniques as tools for assessing soil compaction and to help conclude with the project consortium that In November 2009, during the first trials of low ground-pressure tyres, soil was removed in intact cores from the sites. The cores were measured for saturated hydraulic conductivity by constant head method, bulk electrical conductivity, and bulk density using radiographic imaging. The results show that hydraulic conductivity measurements were inconclusive in revealing reduced compaction under low ground-pressure tyre treatments. The bulk electrical conductivity measurements provided key information on the electrical formation factor of the cores, a measure of the effective porosity conducting electrical current, revealing higher porosity of the soils treated with low ground-pressure tyres. The results of the radiography measurements provided grey-scale images, showing increased bulk density with darker shades. These shades were converted into a range of soil bulk densities for each soil texture. The results revealed that significant impacts to prevailing soil bulk density by the heavy traffic treatments was limited to 0.5-0.8 m from the surface, highlighting a zone of reduced porosity. The radiographs also provided fine spatial resolution of the change in soil bulk density with depth, difficult to achieve with traditional core techniques, revealing that under the low ground-pressure treatments significantly lower soil bulk densities can be maintained. In autumn 2010, during the second trial season of low-ground pressure tyres, the tramline wheelings were photographed and measured for electrical conductivity in-situ. The photographs were taken with a commercial digital SLR camera at three locations along the lengths of the tram line treatments. In pairs, overlapping by 60- 80%, the digital photographs showed a single tramline wheeling, with also ground referencing coordinates. These photographs formed the basis of photogrammetry, the measurement of photographs, and 3-D models of the tramline wheelings (digital terrain models) were generated with Erdas eATE imaging software. The results were of DTMs with a mean RMSE of 0.003 m in the horizontal and vertical plane, with the cleat depressions of the tyres and individual aggregates >0.005 m defined. As a tool to measure soil surface deformation, photogrammetry has increased precision over traditional pin-meter and chain techniques, though requires considerable skill and time to process the photographs.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available