Availability of linuron to plants in different soils

Total uptake of linuron by wheat seedlings in nutrient solutions was close to that expected from the product of the amounts of water transpired by the plants and the concentrations of herbicide in solution. Uptake from 19 different soils was less than the amount supplied by mass-flow when the concentrations of linuron in the soil solution were estimated from slurry adsorption measurements. Using a pressure-membrane technique, it was shown that the actual soil solution concentrations of linuron were less than those estimated, and following rewetting of pressure-membrane samples, the rate of redistribution of linuron between the adsorbed and solution phases was slow. The results suggest that under the conditions of the uptake experiments, the systems were not in equilibrium, and show that the rates of adsorption and desorption of linuron may be important in determining its availability to plants.     

Persistence of 2,4,5-T in a heavy clay soil

The persistence of the herbicide 2,4,5-T was studied at different controlled temperatures and moisture levels in Regina heavy clay. Degradation approximated to first-order kinetics and the half-life varied from about 4 days at 35°C and 34% soil moisture to about 60 days at 10°C and 20% soil moisture. The laboratory data were used in conjunction with the appropriate measurements of surface soil temperature and moisture content in the field to simulate the degradation pattern for the herbicide in five separate micro-plot experiments. Satisfactory agreement with the observed patterns of loss was obtained in two of the experiments but in the other three, the model over-estimated rates of loss. It is suggested that the reason for this was the difficulty of obtaining a correct measure of soil moisture content to use in the simulation program.     

Comparison of solvent systems for extracting herbicide residues from weathered field soils

The extraction from several field soils of the four herbicides benzoylprop-ethyl, nitrofen, profluralin, and tri-allate applied at least 6 months previously was compared using six solvent systems. The residues extracted were quantified using gas chromatographic techniques. Similar recoveries were achieved using 30% aqueous acetonitrile or acetonitrile + water + glacial acetic acid mixtures. The presence of the acetic acid was found to increase residues extracted only in the case of tri-allate. Methanol and 10% aqueous acetonitrile were slightly less efficient in recovering residues from the weathered field soils whereas acetone tended to be a poor solvent for the extraction of the chemicals studied.     

Sampling Shrimp Populations in Hatcheries

Abstract.– Shrimp populations were estimated with volumetric sampling techniques during different phases of hatchery operations. Factors considered which might effect precision of estimates included stage age, density and temperature. Estimates of nauplii were obtained with coefficient of variation values smaller than 3% when nauplii were concentrated in 20-L buckets and smaller than 8% when released in 13,000 L of water in larval rearing tanks. In both cases estimates were of sufficient precision to make management decisions for routine hatchery work. A technique was developed for estimating shrimp populations in larval rearing tanks with coefficient of variation values smaller than 15%. Volumetric sampling of postlarvae older than PL₄, in larval rearing tanks was highly variable due to the tendency of shrimp to congregate and attach to tank walls and bottoms. A direct relationship was observed between postlarval density and the precision of population estimates in harvest buckets. Water temperature and postlarval age did not affect precision at the densities and ages studied. These findings have important implications for commercial transactions. Industry standards utilizing coefficient of variation are recommended for larvae and postlarvae population estimates.     

The effects of IgG2 and of antigen concentration on prozoning in the complement fixation test for bovine brucellosis.

Addition of Brucella-specific IgG2 to solutions of Brucella-specific IgG1 initially induced prozoning and at higher concentrations prevented all reaction in the complement fixation test (CFT) for bovine brucellosis. Some infected cattle may be diagnosed as brucellosis-free due to a high ratio of specific IgG2 to IgG1. Increasing the concentration of antigen in the CFT reduced the tendency to prozone.