10-year interdisciplinary monitoring of organic stocklass, vegetable rotations at Warwick-HRI, Kirton, South Lincolnshire, UK

Interdisciplinary monitoring of an organic stockless farming system has been carried out over ten years on a fertile silty clay loam in the main vegetable production area of the UK. The results draw together economic outcomes with agronomy, soil science and agro-ecology. Organic management has been used at the Kirton research site since conversion of a 3.2 ha unit in 1997. There is great variability in crop yields and marketing results but overall a successful ongoing vegetable production system has been established. Soil fertility, weeds, pests and diseases have been managed successfully without imports of animal manures or green waste compost. Production costs are well controlled and marketable yields are good. However, because the site is a research farm, the actual marketing of produce was sometimes weak and caused a low farm net margin. The site contributes valuable information to the European network of long-term fi eld experiments in organic farming for this particular farming system

The role of regulatory mechanisms for control of plant diseases and food security — case studies from potato production in Britain

Being aware of the potentially devastating impacts of plant diseases on food security, governments have designed and employ plant health legislation to prevent or inhibit the worst impacts. The development of such policies in Britain, and latterly in Europe, can be closely linked to disease events that have occurred in the potato sector. We analyse early and current examples of policies governing potato diseases in Britain to identify the decision processes leading to the implementation of such phytosanitary policies and how they have evolved over time and in response to different disease threats. Reasons for developing and implementing phytosanitary policies include the desire to prevent pathogens being introduced (entering and establishing in a new area), the protection of export markets, and the lack of effective control measures. Circumstances in which regulatory policies would not be appropriate could include situations where a disease is already widely distributed, unacceptable costs, lack of exclusion measures, or difficulties of disease diagnosis. We conclude that in general, government policies have worked well in protecting British potato growing over the last one hundred years, despite of the failures of some of the policies discussed here. They have also contributed much to the development of plant health policies for other crops. Voluntary grower initiatives are a new mechanism complementing existing formal policies with an additional level of security that allows individual growers to take on additional responsibility rather than relying entirely on government legislation

Investigation of factors controlling the dynamics of beach surface moisture content

This dissertation investigates the factors that control beach surface moisture dynamics. The study consists of a suite of laboratory and field experiments to document, analyze, and model the role of the key input parameters (groundwater table fluctuations, capillary actions (i.e., moisture retention, hysteresis, and hydraulic conductivity), evaporation-condensation, and sediment size) on the spatio-temporal variability of beach surface moisture content. Results from the laboratory experiments demonstrated that the capillary processes of hysteresis and hydraulic conductivity heavily influence the spatial and temporal dynamics of beach moisture. Additionally, different sediment grain sizes produced marked differences in capillary processes within the sediment column, under the same hydrological conditions. Analysis of evaporation dynamics reveals that evaporation from the beach surface differs dramatically from that of a free water surface. Initially, evaporation of moisture occurs almost entirely at the surface layer and at a rate that approximates the potential evaporation rate. However, after this time period the rate of evaporation at the upper surface layer stabilizes and remains approximately constant and the sub-surface layer becomes the dominant source of moisture for evaporation. Field measurements of surface moisture content demonstrated that spatially the beach surface can be characterized by three moisture-content zones: a consistently dry back beach zone, a variable content zone, and finally a persistently wet fore beach zone. Temporally, moisture contents varied over both short-term (daily) and long-term (multi-day) sequences. Over the short-term, diurnal fluctuations in the groundwater table played a significant role in influencing surface moisture across the wet and variable-content zones, whereas evaporation and condensation processes were the dominant factors in the dry zone. Over the longer term, variations in the lunar spring/neap tidal range produced distinct changes in the range of moisture contents, as it regulated the amplitude of the beach groundwater table over multi-day time scales. Modeling of surface moisture content demonstrated that a hysteresis based modeling approach provides a quite accurate and thorough representation of field-measured beach surface moisture dynamics. Simulations revealed that the inclusion of evaporation only influences predicted surface moisture contents across the dry back beach, whereas simulations across the wet fore beach and moisture variable middle beach are virtually unchanged by the inclusion of evaporation

Investigation of utility of Delta-T Theta Probe for obtaining surficial moisture measurements on beaches

Recent studies have reported on the use of a new device to measure beach \u27surface\u27 moisture content, the Delta-T Theta Probe. However, the sensor length (6.0 cm) is too long for measurement of true surface moisture conditions. This study investigated the reliability of the Theta Probe as sensor length is reduced to lengths of 1.5, 1.0, and 0.5 cm. Field investigations were conducted at sites in Texas and North Carolina, in order to evaluate the influence of differing sediment sizes on probe output. It was found that calibration R^2 values remained high and only a minimal increase in standard error occurred as the length of the sensor rod array was shortened. However, the sensitivity of the Theta Probe response to changes in moisture content was influenced by the length of the sensor rod array, weakening as sensor length was reduced. Sediment size does not influence the calibration strength or accuracy of the Theta Probe, as the R^2 values and SE values are not significantly different at the 95% confidence interval between grain sizes. Comparison of multiple calibration repetitions and different probes showed that the Theta Probe is reliable and the probe units are interchangeable

Corrosion Study of AA2024-T3 by Scanning Kelvin Probe Force Microscopy and In Situ Atomic Force Microscopy Scratching

The localized corrosion of AA2024-T3, and the behavior of intermetallic particles in particular, were studied using different capabilities of the atomic force microscope (AFM). The role of intermetallic particles in determining the locations and rates of localized corrosion was determined using scanning Kelvin probe force microscopy in air after exposure to chloride solutions. Al-Cu-Mg particles, which have a noble Volta potential in air because of an altered surface film, are actively dissolved in chloride solution after a certain induction time. Al-Cu-(Fe, Mn) particles are heterogeneous in nature and exhibit nonuniform dissolution in chloride solution as well as trenching of the matrix around the particles. Light scratching of the surface by rastering with the AFM tip in contact mode in chloride solution results in accelerated dissolution of both pure Al and alloy 2024-T3. The abrasion associated with contact AFM in situ resulted in the immediate dissolution of the Al-Cu-Mg particles because of a destabilization of the surface film.This work was supported by the Air Force Office of Scientific Research under contact no. F49620-96-1-0479, Major H. De Long, Administrator. P. S. was partially supported by the Swiss National Foundation of Research