No description available.

No description available.

No description available.

A linear programming (LP) model is formulated to reflect economic, climatic conditions, and cultural practices followed in the pot flower industry of Quebec. The objective is to determine the optimal crop mix that maximizes net returns and optimizes space usage given production and marketing constraints. Decision variables are composed of nine major pot flower varieties with several pot sizes produced for different marketing periods during the year. Data are collected from producers in the Montreal area in 1990, and is supplemented by interviews with ornamental counsellors and citations of governmental publications. / Results have shown that the use of LP as a design tool can be of benefit to ornamental producers and managers in decision making. Increasing the amount and quality of available information to producers can lead to improved decisions that increase production efficiency and space productivity, and thus lead to a more competitive industry.

Three drainage experiments were conducted on a newly developed organic soil where three cultural methods were superimposed. Measurements of carrot yields, subsidence, water table fluctuations, subsurface drain performance, hydraulic conductivity and soil bulk density were made. Rotovating the soil produced higher carrot yields than plowing or disking during the first year. The seven-year subsidence totalled 515 mm and depended mostly on organic soil depth. Hydraulic conductivity values did not change after five years of drainage. Bulk density of the top 0.20 m increased by 71% in 6 years, whereas the values down the profile increased between 3.3 and 16.2%. / The effect of two water table depths (WTD), 0.6 and 0.9 m, in an organic soil on soil water tension, subsidence swelling and carrot yields was studied in undisturbed cores in the greenhouse. Carrot yields were reduced by the 0.9 m WTD. Subsidence with the 0.9 m WTD was more than double that of the 0.6 m WTD. Raising the water table near the surface caused the soil to swell. / Hydraulic conductivity, bulk density, fiber content and drainable porosity were measured in undisturbed organic soil profiles. Values from all four properties decreased with increasing depth.

Earthworms have an important role in the decomposition of organic matter, mineralization of nutrients and physical mixing of soils. Despite a large number of laboratory and greenhouse-level studies investigating how earthworms modify soil properties and promote soil fertility, we lack reliable methods to scale-up and quantify earthworm contributions to nutrient cycling at the agroecosystem level. The objective of this thesis is to determine the influence of earthworm communities on nitrogen (N) transformations in soils and to quantify their contribution to nitrogen flux through soils for soybean and maize cropping systems of Quebec. Laboratory growth rates were used to predict how earthworm growth responded to seasonal fluctuations in soil temperature and moisture. The relationships between earthworm populations, soil-N pools and annual crop production were evaluated in a field experiment. When favourable conditions occurred in 2004 (temperatures <20°C, and rainfall at least once a week), a positive relationship was found between earthworm numbers and the plant available-N, including soil mineral-N, microbial biomass-N and total-N removed in soybean grain. In 2005, soil conditions were unfavourable (temperatures > 20°C and little or no rainfall) to earthworm survival and growth, and no relationship was found between earthworm populations, soil N pools and corn production. These data permitted me to make assumptions about earthworm activity and life histories under field conditions, which were used to estimate N flux through earthworm communities with two models. The models were tested for their sensitivity to varying parameter values within the range reported in the scientific literature. During a crop growing period with favourable climate conditions, a large earthworm population (100 g fresh weight biomass m-2 or greater) is predicted to cycle as much as 120 kg N ha-1. Model predictions were very sensitive to input parameters and did not correspond to the partial N budget calculated at the site. Accurate predictions of N mineralization by earthworms require more species- and site-specific parameter values. Further investigation using stable 15N isotopes as tracers would help us to follow the N transformations and evaluate the N flux mediated by earthworms at the field scale.

No description available.

No description available.

The economy of Quebec suffered for many years of persistent unemployment and skilled labour shortages that the market could not eliminate, neither government intervention as the number of youths enrolled in vocational programs at high school and college dropped of 50% in one decade. / Could we adjust vocational training so that it responds efficiently and usefully to the needs for skilled labour? This can hardly be achieved as the role of the educational system in that respect is not well defined, programming is inadequate, training for youths is not a priority, and its resources are as scarce as the information available to evaluate its profitability or to choose the most efficient set of programs. / To attain this conclusion, we reviewed surveys on training in firms to estimate if it takes advantage of all available social benefits. Their results did not allow such finding but revealed that Quebec firms train less than elsewhere in Canada, that training is the prerogative of firms experiencing hiring problems and targets mainly a skilled, educated and well paid labour force. Therefore, the intervention of the government lies within a distribution of responsibilities where vocational training supplies skilled labour to which those firms with more specific needs will add complementary skills. / Years ago, the vocational training system was well fulfilling this task as training institutions were one source of skilled labour favoured by Quebec firms. This has since changed. Our original analysis of the efficiency of vocational programs confirmed their inadequacy to the needs, especially at high school level, as most skills taught target occupations affected by chronic labour surpluses. (Abstract shortened by UMI.)

Objective. To describe the factors predictive of hepatitis A disease severity. / Design and setting. Cross-sectional study of hepatitis A cases during the recent HAV outbreak in the Montreal gay community. / Subjects. All 631 hepatitis A cases documented in the Montreal-Centre region between November 1994 and December 1996. / Outcome measures. Hepatitis A severity was operationalized as (1) the need for hospitalization and (2) a symptom severity index (vomiting, dark urine and abdominal pain). / Results. Subjects were predominantly male (84%). Homosexual behaviour was reported in 68% of cases. Prevalence of a high severity index was 8%, and 12% of cases required hospitalization. Non parenteral drug use was the only factor predictive of both hospitalization status and severity index. Our data could not establish homosexual behaviour as a determinant of disease severity. / Conclusion. Non parenteral drug users are at increased risk of suffering from a severe disease when infected with the hepatitis A virus. In addition to the current recommendation for routine vaccination of travelers and of homosexual men, drug users could benefit from immunization against this virus.