Effect of exchangeable sodium percent on surface sealing
Abstract Laboratory studies were conducted to evaluate the effect of exchangeable sodium percent (ESP) on soil surface sealing and of surface sealing on infiltration and evaporation processes. Surface seals with hydraulic conductances 52.20 × 10 −3 , 49.20 × 10 −3 , 39.00 × 10 −3 , 33.00 × 10 −3 , and 17.91 × 10 −3 h −1 were attained on top of a sandy loam soil with ESP of 4 by placing a 5-mm layer of the same soil with ESP's 6, 10, 20, 30, and 60 respectively. Surface sealing increased with increasing ESP and appeared complete at ESP 30. Evaporation remained unaffected by the seals. Infiltration, however, was considerably reduced. Soil water profiles, which largely depended on the amount of infiltrated water, tended to become uniform. Equal moisture contents were also observed under evaporation.
Impact of Sodium and Potassium on Environmental Systems
Health effects associated with sodium-cycle water softening has led to the consideration of potassium-cycle ion exchange as an attractive alternative. Regulatory agencies, however, have expressed concern regarding the environmental impacts associated with discharge of potassium-laden brine. To assist in providing guidance regarding the relative environmental impacts deriving from discharge of sodiumand potassium-cycle softener regeneration brine, this article summarizes available literature exploring systems potentially impacted by brine discharge. The literature indicates that replacing sodium chloride with potassium chloride as a water softener régénérant appears to result in a more environmentally benign scenario and may, in certain circumstances, be environmentally beneficial. Some areas where potassium chloride may be advantageous are land application of sewage sludge, viral inactivation, mobility in soil, effects on soil properties and impacts on plant life. There are no significant differences between sodium chloride and potassium chloride in effect on engineered physicochemical processes of in aquatic life systems. The impact of sodium may be detrimental to the environment because the uptake of phosphorus by algae was reportedly enhanced by sodium. Potassium, on the other hand, was not reported to enhance phosphorous uptake. Some questions remain about the impact of potassium and sodium on septic tank bacteria, biological waste treatment processes, and effects on natural flora. The literature reviewed on these topics was somewhat conflicting. Further efforts to assess the impact of potassium and sodium should be directed at resolving these literature discrepancies. •This study was supported, in part, under a grant from Kalium Canada Ltd., Regina, Saskatchewan.
Genotypic diversity in field isolates of Babesia bovis from cattle with babesiosis after vaccination.
OBJECTIVE
To determine whether particular genotypes of Babesia bovis were common to field isolates obtained from cattle properties in Queensland where the B bovis vaccine had apparently failed.


DESIGN
A comparative study of polymerase chain reaction genotypes in different populations of B bovis.


PROCEDURE
Two polymerase chain reaction assays were applied to analyse DNA extracts of B bovis vaccine (K, T and Dixie strains) and 27 field isolates from 24 properties where disease outbreaks had occurred despite the use of the vaccine. To evaluate the stability of the genotypes identified, 11 of the field isolates were inoculated into experimental cattle that had either been previously vaccinated with T strain or not vaccinated.


RESULTS
No particular genotype of B bovis was responsible for the problems observed in previously vaccinated herds. None of the isolates had genotypes identical to the vaccine strains used. No geographic trends among the genotypes were observed. Isolates that originated from the same property also had different genotypes. Blood passage of the 11 field isolates in either previously vaccinated or nonvaccinated cattle did not alter the original genotype.


CONCLUSION
No particular genotypes identified by the Bv80 and BvVA1 polymerase chain reaction assays could be associated with vaccine failures.