Compaction of a swelling clay soil by agricultural traffic; effects upon conditions for growth of winter cereals and evidence for some recovery of structure

A swelling stagnogley soil remained unwheeled or was uniformly wheeled by a combine harvester and a tractor in two successive autumns before direct drilling winter cereals. Combine wheeling of the soil at its wettest condition caused the largest loss of soil porosity. The autumn and spring of the second growing season for the winter cereals were wetter than long term average. The smaller porosity in the wheeled soil, created lower soil redox potential and smaller oxygen flux as well as greater soil strength and larger amounts of available water, but little difference in soil temperature. The crop in the wheeled soil had fewer plants, less root and a lighter yield than in the unwheeled soil. The wheeled soil recovered some porosity and lost strength after wetting and drying during the second growing season, whereas soil freezing had very little effect. This restructuring was sufficient to reverse some of the detrimental effects of compacting the soil.     

The effects of formalin, malachite green and suspended solids on the respiratory activity of rainbow trout, Salmo gairdneri Richardson

Abstract. The influence of formalin and malachite green on ventilation rate, cough rate and oxygen consumption rate of rainbow trout, Salmo gairdneri Richardson, was investigated. The effect of suspended silt on these parameters is also described. In all cases ventilation rate increased by up to 60%. Cough rate increased more dramatically by up to 300%. Some acclimation to the various treatments was observed. Rates of oxygen consumption increased markedly in all cases but particularly when the fish were exposed to silt, when an increase of 500 to 700% was noted. These data emphasize the need for stress-free husbandry when using prophylactics or disease treatments and demonstrate the high oxygen demand of fish in these conditions.     

The use of yttrium oxide and the effect of faecal collection timing for determining the apparent digestibility of minerals and trace elements in Atlantic salmon (Salmo salar, L.) feeds

The effectiveness of the external marker yttrium oxide (Y₂O₃) and sampling period for determining the apparent digestibility (AD) of minerals and trace elements within Atlantic salmon feeds were compared. Yttrium oxide was compared at inclusions of 0.01, 0.1, 1 and 10 g kg^?1 wet weight of the feeds. Samples were analysed for a range of mineral and trace elements via inductively coupled plasma optical emission spectroscopy after wet decomposition with concentrated nitric acid. Feed marked with 1 g kg^?1 provided the greatest recovery, and provided analytical values within an optimal range, and therefore, the effect of faecal sampling period on AD of mineral and trace element was then compared using the feed marked with 1 g kg^?1 Y₂O₃. Faeces were collected over three different time periods within a 24 h period: 4 × 6 h, 2 × 12 h and 1 × 24 h. Magnesium, manganese, phosphorus, iron and chromium displayed significant differences in AD relating to sampling period. An inclusion level of 1 g kg^?1 Y₂O₃ and faecal sampling over at least an 18 h period after feeding proved to be the most effective method of determining AD of mineral and trace element in Atlantic salmon feed.     

THE RESIDUA SYSTEM OF CHEMICAL WEATHERING: A MODEL FOR THE CHEMICAL BREAKDOWN OF SILICATE ROCKS AT THE SURFACE OF THE EARTH

The residua system of chemical weathering is here defined as the chemical sink towards which the bulk of earth's surface materials (i.e. the silicate rocks) trend during weathering. Chemically the system is defined in terms of four major components, SiO₂–Al₂O₃–Fe₂O₃–H₂O, evidence being derived from relative solubilities of components under earth-surface conditions; from experiments in which weathering environments have been simulated in the laboratory; and from field studies of rocks and their weathered mantle. The residua system can be used as a framework to construct mineral facies diagrams showing assemblages of the commonest earth-surface minerals that occur within it: quartz, gibbsite, goethite, kaolinite, halloysite. In a qualitative manner the facies diagrams can then be interpreted in terms of the partial pressure of water (PH₄O) and the temperature, T. The usefulness of this approach in systematizing studies of soil genesis is illustrated with reference to the weathering of granite.