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Introducing loads onto the soil via pneumatic tyred equipment is the major cause of compaction of agricultural soils, which causes damage to the soil-water-air-plant system. The degree of soil compaction is largely influenced by the loads applied to the soil and resulting surface and subsurface pressure. Therefore, this study was conducted in order to determine an effective method to measure the pressure distribution under a selection of pneumatic agricultural tyres on a hard surface and in the soil profile. As a result of this, it has been possible to evaluate the influence of tyre inflation pressure, load, ply rating and tread pattern on the resulting pressure. Also, the carcass stiffness of the tyres studied was determined and alternative methods to predict the carcass stiffness were evaluated and an improved technique was developed. Cont/d.

Organically managed land has increased to 4 % of the total area of agricultural land in the UK. Changing land management can impact upon the rural environment (soils, hydrology and biodiversity) and rural community (socio-economics and culture). This thesis aims to compare the effects of organic farming practices on soil physical, chemical and hydrological properties in relation to conventional farming systems. The research combines data from three different scales: field measurements, plot measurements and catchment modelling. At the field scale: 16 pairs of farms (organic and conventional between 50 and 3000 m apart) located in England, over a range of soil textures: clayey, silty, medium and coarse were investigated. There were also two different land uses (grass and winter wheat). Data was obtained on soil properties including: shear strength, Atterberg limits, field capacity, aggregate stability, HOST values, infiltration rates and Soil Organic Carbon (SOC). The analysis of the data shows that, whilst it is possible to detect the effects of both soil texture and land use (grassland / arable) on a number of the soil properties; there is no evidence that organic farming improves soil properties or physical condition - equally there is no detrimental effect. This is in agreement with the results of a number of other European studies. There was evidence to show that infiltration rates are greater on organically managed grassland than conventional grassland; which agrees with the HOST analysis where fewer fields were degraded under organic management. Fewer traces of pesticides and herbicides were in the soil water from the organic fields compared with the conventionally managed fields; none were at a level which would contribute to agricultural pollution. Cont/D.

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.

Soil compaction is an inevitable consequence of mechanised farming systems whose machines are degrading soils to the extent that some are considered uneconomic to repair. A number of mitigating actions have been proposed but their ability to reduce or avoid damage has not been well tested. The aim of this research was to determine whether actions to reduce damage have been, or are likely to be effective and to assess whether the practice of controlled traffic farming (confining all field vehicles to the least possible area of permanent traffic lanes) has the potential to be a practical and cost effective means of avoidance. The literature confirmed that soil compaction from field vehicles had negative consequences for practically every aspect of crop production. It increases the energy needed to establish crops, compromises seedbed quality and crop yield, and leads to accelerated water run-off, erosion and soil loss. It is also implicated in enhanced emissions of nitrous oxide and reduced water and nutrient use efficiency. Replicated field trials showed that compaction is created by a combination of loading and contact pressure. Trafficking increased soil penetration resistance by 47% and bulk density by 15% while reducing wheat yield by up to 16%, soil porosity by 10% and infiltration by a factor of four. Low ground pressure systems were a reasonable means of compaction mitigation but were constrained due to their negative impact on topsoils and gradual degradation of subsoils whose repair by deep soil loosening is expensive and short lived. Controlled traffic farming (CTF) was found to be practical and had fundamental advantages in maintaining all aspects of good soil structure with lowered inputs of energy and time. On a farm in central England, machinery investment with CTF fell by over 20% and farm gross margin increased in the range 8-17%.