A FLOTATION METHOD FOR THE RAPID MEASUREMENT OF THE WET BULK DENSITY OF SOIL CLODS

A flotation method for the rapid measurement of the wet bulk density of soil clods is described in which the clods are sprayed with a waterproof coating of a resin and then immersed sequentially in liquids of different specific gravity. It is compared with the wax coating method for a selection of soil textures and moisture contents and shown to be ten times as rapid when used to measure wet bulk density with an accuracy of ± 0.05 g cm^-8. The flotation method was used to show that, for three contrasting soils, clod wet bulk density is independent of clod size.     

A survey of clover and Lotus rhizobia in Northern Ireland pasture soils

192 sites covering the main soil types in Northern Ireland were analysed for numbers and effectiveness of clover and Lotus rhizobia, and chemical properties. Peat sites were generally highly acid (pH <5.5) and mineral sites near neutral (pH 5.5–7.8). Clover rhizobia were generally absent from peat sites and present in mineral sites as large populations (> 10⁶ g^?1 dry soil). 79% of isolates were effective on T. repens var. Grasslands Huia. Lotus rhizobia were generally absent from peat sites, less often present than clover rhizobia in mineral sites, and as smaller populations. They were mainly effective on L. pedunculatus var. G4705 and were all of the slow-growing type belonging to the genus Bradyrhizobium. Numbers of clover rhizobia were significantly correlated with soil pH, exchangeable Ca, base saturation and Al saturation, but effectiveness of clover rhizobia and numbers of Lotus rhizobia were not correlated with any soil chemical property.     

Separation of complete and incomplete Rh antibodies by centrifugation

The ultrasonic dosages given in W. J. Fry et al., "Ultrasonic lesions in the mammalian central nervous system" [Science 122, 517 (1955)] should be corrected as follows: For the lesion illusrated in Fig. 1, the dosage was 40 atm acoustic pressure amplitude and 3.9(10(2)) cm/sec acoustic particle velocity amplitude. For the lesions illustrated in Figs. 2 and 3, the dosage was 41 atm acoustic pressure amplitude and 4.0(10(2)) cm/sec acoustic particle velocity amplitude.     

LIQUID LIMIT DETERMINATION OF ARABLE TOPSOILS USING A DROP-CONE PENETROMETER

The drop-cone method, in which a 30° cone of mass 80 g is allowed to sink into a soil sample at a selection of moisture contents, is described and examined as a possible alternative to the Casagrande device for liquid limit determination. The methods are compared for 13 arable topsoils. The drop-cone method, which uses apparatus that is readily available commercially, is shown to have advantages in ease of conduct of the test and in greatly improved reproducibility between operators.     

The soil solution chemistry of some Oxfordshire soils: temporal and spatial variability

The immiscible liquid displacement method was used to displace soil solutions from a variety of Oxfordshire soils. These included grassland, arable, and woodland soils. The results of detailed chemical analyses demonstrated that for most solutes there were significant seasonal differences as well as differences both within and between soil series. The variation over time intervals of a few days or weeks appeared to be relatively small in relation to sampling errors. Median concentrations (in mmol m⁻³) for soil solutions derived from 21 grassland sites and six arable sites sampled six or seven times throughout 1 year were: _pH 7.7, alkalinity 1810, Na 465, K 390, Mg 135, Ca 2120, Sr 1.9, Ba 0.16, Mn 0.52, Fe 3.4, Cu 0.25, TON 860, Cl 1590, S 327, P 64, Si 220, B 5.1, and DOC 4250. For many solutes, the individual soil solution concentrations spanned a range from approximately five-times less than these median values to approximately five-times more.     

THE PLASTIC LIMIT, AS DETERMINED BY THE DROP-CONE TEST, IN RELATION TO THE MECHANICAL BEHAVIOUR OF SOIL

The variation with water content is examined of soil cohesion, soil-metal friction, susceptibility to soil compaction, implement draught and the slope and intercept of the virgin compression line of critical state soil mechanics theory. For a given soil, all these relations are shown to exhibit turning points at a similar water content which corresponds to the cone penetrometer plastic limit, as determined with a drop-cone penetrometer, rather than the Casagrande plastic limit. The cone penetrometer plastic limit, which can also be more reliably determined than the Casagrande plastic limit, is the better indicator of soil behaviour in the field and of the water content at which the soil changes from the brittle to the plastic state.     

Soil structural quality, compaction and land management

Soil compaction is a concern worldwide, particularly where compactible soils are used for intensive agriculture in a wet climate. We have investigated the impact of compaction and the associated changes in soil structural qualities on crop production and environmental pollution. The overall objective was to develop soil management systems that provide suitable conditions for crop growth and minimize environmental damage. We ran large-scale field experiments studying the preservation of structural quality in arable and permanent grassland, using management systems such as the control or elimination of field traffic and the application of conservation tillage and zero tillage. We measured bulk density, shear strength, cone resistance, macroporosity, relative diffusivity, air permeability and water infiltrability to identify soil qualities that could be used for selecting suitable soil management. Along with crop yield, we measured environmental impacts, such as the emissions of nitrous oxide from the soil, which require the interaction of soil structure and water content near the soil surface. Soil structure influenced wetness, which affected trafficability, compaction and nitrogen retention. Measurement of properties that affect fluid storage and transport, such as macroporosity, provided soil quality indices that helped in recommending suitable soil management systems. Spatial variation of structure associated with wheel-track locations could be estimated rapidly using a cone penetrometer. Variation was particularly important in determining crop yield consistency. Crop productivity and soil structural qualities were preserved best when field traffic was eliminated. A reduced ground-pressure system successfully minimized compaction in grassland but was less effective in an arable rotation. Unless traffic is eliminated, good timing of operations is the most effective way to preserve soil structural quality.     

Contagious ecthyma in the live sheep export industry

Objective: To investigate control options for contagious ecthyma (scabby mouth) in Australian sheep exported live to the Middle East.
Design: Prevalence, vaccination and modelling studies.
Procedure: One hundred and forty weaner sheep (less than 1 year old) on each of 106 farms in Western Australia (WA) and 18 farm groups of adult wethers received at a WA commercial feedlot were examined for lesions of scabby mouth. Sheep on a total of 26 farms in 3 States were divided into treatment and control groups for the vaccination study. A simple deterministic compartmental model was developed to establish which parameters had the greater effect on disease prevalence.
Results: The proportion of farms with evidence of scabby mouth in weaner sheep was 23.6% and, on those farms with the disease, the overall prevalence was 6.1%. At the feedlot, 4 out of 18 farm groups had 5 or more sheep with lesions on arrival. The overall prevalence in the 4 diseased groups was 5.2%. Sheep vaccinated on farm before trucking to the feed-lot had a lower prevalence of scabby mouth at the end of simulated shipping than controls. The main determinant of scabby mouth prevalence was the proportion of sheep immune to the disease.
Conclusion: A program of vaccination for scabby mouth will reduce the prevalence of disease during live export. However, using current technology it is not possible to deliver shipments of sheep to the Middle East that are guaranteed completely free of scabby mouth.     

The effect on the contralateral stifle joint of sectioning of the cranial cruciate ligament in the dog

In three adult dogs the cranial cruciate ligament of the right stifle was sectioned. The animals were examined at regular intervals over the following twenty-nine months and the clinical findings noted. Fluorochrome bone markers were injected at intervals of approximately six months. Following injection of barium sulphate and Berlin blue after euthanasia, the joint tissues of both stifles were examined for evidence of degenerative changes. The right stifles showed typical changes of osteoarthritis, while the left stifles revealed no abnormality.