The surgical correction of a deviated anterior maxilla in a horse

SUMMARY The surgical correction of facial deformities of the horse have rarely been undertaken. The surgical and medical management of submucous clefting of the anterior maxilla in a young colt is described.     

In-field calibration of a dielectric soil moisture meter designed for use in an access tube

Abstract. The in-field calibration of a dielectric probe to measure soil water content is described. The probe uses an access tube analogous to that of the neutron probe. The dielectric constant was measured at soil depths of 10, 20, 30, 40, 60 and 100 cm. Cores of soil were then taken from the face of pits dug 30 cm from the access tube and their soil water contents determined by oven drying. The dielectric constant values measured by the probe were calibrated against water contents from these cores. We found that sensor depth needed to be included to achieve a good calibration model that explained 72% of the variance. It is argued that depth needs to be included because of artefacts introduced during the installation of the access tube.     

Enhanced efficiency of electrostatically charged insecticide aerosols

The bioefficacy of a standard domestic aerosol insecticide has been compared with that of a similar spray in which the droplets were electrostatically charged. The aerosol was charged without the need for an external power supply, by enhancing natural charge separation processes that occur during atomisation. The charge-to-mass ratio achieved was 1.1 x 10(-4) C kg-1, compared with 2.2 x 10(-5) C kg-1 for the standard aerosol. Efficiency was assessed for insects in free flight. A direct space-spray application method was used to study the bioefficacy of these aerosols on houseflies, Musca domestica, and an indirect space-spray method on houseflies and mosquitoes, Culex quinquefasciatus. Two levels of concentration of active ingredients were compared. At low concentrations of 1.57 g kg-1 of bioallethrin and 0.29 g kg-1 of bioresmethrin, the charged aerosol achieved a significant reduction in KDT50 (time at which 50% of the flies were knocked down), compared with the standard aerosol. In the direct spray application to houseflies, the KDT50 was reduced by 50%, while in the indirect spray the KDT50 was reduced by 40%. In the indirect spray of mosquitoes, the KDT50 was reduced by 22%. With higher active ingredient concentrations of 2.09 g kg-1 for bioallethrin and 0.39 g kg-1 for bioresmethrin, the charged aerosol also demonstrated faster knockdown than the standard, but the improvement was less marked. In the direct spray application to houseflies, the KDT50 was reduced by 21% compared with the standard aerosol, while in the indirect spray the KDT50 was reduced by 16%. In the indirect spray of mosquitoes, the KDT50 was reduced by 24%. The percentage mortality after 24 h was also increased with the charged aerosol. Charge carried by the droplets results in increased interception of the insecticide, as the droplets are attracted to the insects in flight and space charge effects within the aerosol could cause improved dispersion in the test chamber.     

Adverse effects of simulated harvesting of short-rotation willow and poplar coppice on vertical pressures and rut depths

Little is known of the effects of mechanized harvesting on ground conditions during the harvesting of short-rotation coppice. An investigation was therefore carried out in which different vehicles were used to simulate the effects of wheeling from heavy and light harvesters and crop removal equipment. The experiments were carried out on sites containing Bowles hybrid willow (Salix viminalis) and poplars (Populas rap) and on clay and sandy loam soils. The effect of different vehicles was assessed in terms of rut damage and direct measurements of soil stress using buried sensors. Maximum stresses measured 0.3 m below tractor wheels ranged from 50 to 200 kPa, but the greatest stresses, 350 kPa, were recorded under laden trailer wheels. Maximum stresses measured beneath crawler tracks were only 25 kPa. Similarly, substantial ruts were caused by vehicles simulating wheeled harvesters, the deepest ruts were caused by laden trailers but crawler tracks created least disturbance. Wheeling was carried out at soil water contents above the plastic limit and the deepest ruts were created on clay rather than sandy loam soil. The effects of the stresses generated in the soil could impede future root growth, and the deeper ruts formed could damage existing root systems of coppice.     

Measurement of the size distribution of water-filled pores at different matric potentials by stray field nuclear magnetic resonance

The water retention characteristic provides the traditional data set for the derivation of a soil's pore‐size distribution. However, the technique employed to achieve this requires that assumptions be made about the way pores interconnect. We explore an alternative approach based on stray field nuclear magnetic resonance (STRAFI‐NMR) to probe the water‐filled pores of both saturated and unsaturated soils, which does not require information relating to pore connectivity. We report the relative size distributions of water‐occupied pores in saturated and unsaturated samples of two sets of glass beads of known particle size, two sands, and three soils (a silty loam, a sandy loam and a loamy sand), using measurements of the NMR T₁ proton relaxation time of water. The T₁ values are linearly related to pore size and consequently measured T₁ distributions provide a measure of the pore‐size distribution. For both the sands and the glass beads at saturation the T₁ distributions are unimodal, and the samples with small particle sizes show a shift to small T₁ values indicating smaller voids relative to the samples with larger particles. Different matric potentials were used to reveal how the water‐occupied pore‐size distribution changes during drainage. These changes are inconsistent with, and demonstrate the inadequacies of, the commonly employed parallel‐capillary tube model of a soil pore space. We find that not all pores of the same size drain at the same matric potential. Further, we observe that the T₁ distribution is shifted to smaller values beyond the distribution at saturation. This shift is explained by a change in the weighted average of the relaxation rates as the proportion of water in the centre of water‐filled pores decreases. This is evidence for the presence of pendular structures resulting from incomplete drainage of pores. For the soils the results are similar except that at saturation the T₁ distributions are bimodal or asymmetrical, indicative of inter‐aggregate and intra‐aggregate pore spaces. We conclude that the NMR method provides a characterization of the water‐filled pore space which complements that derived from the water retention characteristic and which can provide insight into the way pore connectivity impacts on drainage.     

Simulation of solute leaching in soils of differing permeabilities

Abstract. The model described divides the soil into layers and considers two categories of water, mobile and immobile, in each layer. It has two main parameters, one a measure of the soil's capacity to hold water and thence to retain solutes against leaching, and the other a measure of the ease with which water can pass through the soil and carry solutes with it. These are, in effect, capacity and rate parameters, and the model is unusual in having both. They can be estimated from the percentages of clay and other soil components. The rate parameter varied appreciably between plots in the field but in a consistent manner. The model has been validated against field experiments following the vertical movement of solute applied to the soil surface and allowed to leach, and the paper includes one such test.