Dependence of tensile strength of soil aggregates on soil constituents, density and load history

The compressive-tensile stress ratio at failure under unidirectional loading of air-dry samples of 10 soils was compared with their clay and CaCO₃ contents, and their surface areas. Deviations from the commonly assumed Griffith theory were found for two soils. No special relationships were found between soil constituents and associated compressive tensile stress ratio, even though this ratio tends to decrease slightly with increasing clay percentage.     

Lateral Thoracic Artery Axial Pattern Flap in Cats

Objective— To describe the location of the lateral thoracic artery (LTA), determine dimensions of an axial pattern flap based on this artery, and report use of this flap in 2 cats.
Study Design— Ex vivo study and case reports.
Animals— Cat cadavers (n=8); cats (n=2) with thoracic limb skin defects.
Methods— Dissection of the LTA was carried out on 1 side of each cadaver and the contralateral side was used for injection studies. In 4 specimens, the LTA was cannulated and injected with positive contrast material and the flap was raised and radiographed. In 4 specimens, the flap was injected with methylene blue. Adequacy of flap injection was subjectively evaluated and leakage of methylene blue from the cut edge was noted.
Results— The cutaneous location of the LTA caudal to the triceps muscle was confirmed. Mean flap size was 8.7 cm × 15.5 cm for a mature, averaged-sized cat. Perfusion of the entire flap was demonstrated and viability of the flap was confirmed in 2 clinical cases.
Conclusion— The LTA flap is useful for repair of skin defects of the brachium and antebrachium in cats.
Clinical Relevance— The LTA flap is an alternative technique for repair of skin defects involving the thoracic limb of cats.     

Nitrogen mineralization in the field at various soil depths

The accumulation of mineral nitrogen was measured in the field in five soil-layers between 0 and 120 cm, in two plots of a long-term experiment contrasting high and low fertilizer inputs. Soil temperature and moisture were also determined. The total quantity of mineral N that accumulated in the 0-120 cm soil layer during 11 weeks in the summer was 138 and 78 kg ha⁻¹, 25% and 45% of which were found below 60cm, in the high and the low fertility plots, respectively. Nitrogen mineralization in the field was predicted by a model which takes account of changes in temperature and moisture content of the soil. The potentially mineralizable N for this model was found from laboratory incubation experiments. The measured amount of mineralized N was 13 to 26% less than the predicted amount.     

Directional strength in aggregates as affected by aggregate volume and by a wet/dry cycle

Reduction of aggregate size in the upper, tilled soil layer as a result of one wet/dry cycle was observed for sandy soil and clay soils. Bulk density of aggregates tended to increase as their size diminished for the clay after the wet/dry cycle, whereas similar changes in bulk density for the loam were observed only for aggregates smaller than 5.6 cm. Slaking and water-drop impact seem to be the major factors in reducing the aggregate size of the sandy loam, while swelling and shrinkage affect clay aggregates of all size groups, but only aggregates smaller than 4.0 mm for the sandy loam. Tensile strength of the sandy loam aggregates was related to the axis along which the stresses were applied. A definite directional dependence of tensile strength was observed, e.g. the shorter the axis, the larger the tensile strength. The directional strength dependence was apparently not affected by one wet/dry cycle.     

Reduced CO2 release from decomposing wheat straw under N-limiting conditions: simulation of carbon turnover

The turnover of residue carbon in soil containing little available N can affect the management of crop residues. The effects of N deficiency on CO₂ release from decomposing wheat straw were measured in an incubation experiment and interpreted by computer simulation. Straw with a C:N ratio of 91, incubated for 460 days in sand that was inoculated with a soil suspension, released CO₂ much more slowly than when inorganic N was added to obtain a C:N ratio of 5. The evolution of CO₂ continued longer without added N, approaching the amount released in the high N treatment with time. The simulation model NCSOIL was modified to simulate reduced CO₂ release from decomposing residue when N limits microbial growth by (i) including the decomposers' biomass in the rate of residue decomposition in the form of a Monod-type equation, where the biomass reduced the rate when its concentration was small compared with a saturation constant, and (ii) including formation of a polysaccharide-like pool that received the decomposed C that could not be assimilated by the biomass because of insufficient N. The modified model simulated the reduced CO₂ production in the absence of sufficient N, as a result of a smaller microbial biomass that reduced the rate of residue decomposition, and the formation of polysaccharides as long as N limited synthesis of microbial biomass.