In this paper there will be no attempt to give answers to immediate field problems. ,Rather it is hoped to indicate the lines of approach which are being used in studying the physiology of growth of our pasture species
Several species within the genus Serratia (Enterobacteriaceae) have potential for use, or are currently used, in the control of insect pests.However, as with most microbes, exposure to certain UV wavelengths can drastically reduce cell viability.In this study we investigated the effect of exposure to short (254 nm) UV radiation and natural sunlight on strains of Serratia.Exposure to 254 nm for 5-30 minutes killed most Serratia spp.; however, there were considerable strain differences with the LT 50 ranging from 2.9 to 13.7 minutes.Survival time increased to more than 2+ hours under sunlight exposure but was dependent the bacterial broth temperature.
Abstract An examination of factors which could influence the growth of Pithomyces chartarum and the development of facial eczema toxicity in pasture indicated that: 1. 1. Growth and sporulation on dead grass leaves and stems is most rapid under warm (70°F to 80°F) moist conditions. It is retarded by prolonged exposure to high levels of moisture around the dead herbage, and considerably accelerated on tissues with a high content of soluble organic material, e.g., freshly dead, well-nourished leaves.2. 2. The ability of spores to adhere to live leaves is directly related to the wettability of the leaf surfaces.3. 3. The wettability of the lower epidermis of ryegrass leaves is high. The upper epidermis of ryegrass leaves and both surfaces of the leaves of paspalum and cocksfoot are difficult to wet. The lower epidermis of white clover leaves is moderately wettable.4. 4. Spore germination is greatly stimulated by cell exudates from damaged areas on live leaves of ryegrass or paspalum provided the leaves are moist. Dilute juice pressed out from ryegrass leaves has a similar effect on spore germination.5. 5. As judged by nitrogen analyses, considerable quantities of soluble organic material are readily available at the surface of immature leaves of ryegrass if they are wetted after being grown under warm moist conditions. This is not the case with mature leaves.6. 6. Germination of spores followed immediately by a period of rapid mycelial growth in dilute ryegrass juice can lead to a significant rise in facial eczema toxicity within 15 hours.
It is accepted virtually to the stage of being axiomatic that our climate has been of key importance in allowing us to develop an efficient pastoral industry
Abstract A comparison of the effects on vegetative growth of 8 hr. and of 16 hr. of light per day at various temperatures was carried out with 9 species of pasture plants grown in New Zealand. The temperatures used were 45°F, 55°F, 65°F, 75°F, 85°F, and 95°F. The light intensity was constant at approximately 2,700 foot candles. Hence in these experiments an increase in photoperiod from 8 to 16 hr. of light was accompanied by a doubling in quantity of light per day. The influence of the various levels of temperature on the rates of growth and tillering of individual species was similar to that found earlier for plants grown with a 12 hr. photoperiod. However, optimum temperatures tended to be lower with 8 hr. than with 16 hr. of light, particularly for rates of tillering. At the lower temperatures the increase in photoperiod from 8 to 16 hr. generally gave only a small increase for rate of tillering and in some cases possibly decreased it; but it generally more than doubled daily growth on an individual tiller. Such effects were most apparent at 45°F, generally decreased at intermediate temperatures (55–75°F), and in some cases were reversed at 95°F.
Summary The influence of levels of temperature, soil moisture, soil nitrogen status, and of light intensity on the survival of New Zealand strains of ryegrass (Lolium spp.) was examined. It was found that not only was the survival of plants reduced bv soil moisture stress (pF 3.4–4.2 compared with pF 2.6–3.0) and high temperature (80°F compared with 65°F), but also that survival under the low moisture or high temperature condition was much less when there was a high level of nitrogen in the soil. The various effects were additive. In general the survival of plants of perennial ryegrass was significantly better than that of plants of short-rotation and Italian ryegrass. A reduction of light intensity to 20–25% of full daylight also adversely affected survival, particularly when it occurred in conjunction with high temperatures.
Continuous and simultaneous measurements of CO2 exchange and transpiration rates of whole soybean plants were made under contrasting, controlled environmental conditions for periods of up to 3 d. Daytime temperatures and vapour pressure deficits (VPD) were 27.5 °C/12 mb; 27.5 °C/5 mb; 22.5 °C/12 mb, and 22.5 °C/5 mb. Night temperatures were 5°C lower than day temperatures and night VPD was 2.7 mb and 3.5 mb at the higher and lower temperature respectively. The experimental conditions were virtually the same as those under which the plants had been grown. Transpiration rates were higher at the higher VPD but were also influenced by temperature. At 12 mb VPD the rates were 16 per cent lower at 22.5 °C than at 27.5 °C. Temperature had no effect on the transpiration rate at 5 mb VPD. Photosynthesis rates were lower at 5 mb VPD than at 12 mb VPD at both temperatures: the difference was substantially greater (c. 70 per cent) at 22.5 °C. Under all treatments meso-phyll resistance (r'm) appeared to have a major effect on the photosynthetic rate, and varied more than twofold between treatments. r'm was highest in plants grown at 22.5 °C/5 mb VPD and lowest at 27.5 °C/12 mb VPD.
Summary To obtain more definite information than that available to date on the weather conditions associated with outbreaks of facial eczema, the records from climatological stations in districts in which outbreaks of facial eczema frequently occur were examined. The data indicate that a season can be considered potentially dangerous either if the soil temperature at 8 inches, measured at 9 a.m., has reached an average of 62.5°F or over during November, or if the main body of moisture in the soil, as distinct from surface layers wetted by smaller rains, has reached a deficit of 1 ½ in. by the end of November. A more definite judgment can be made by the end of December. It appears there is a high probability of subsequent outbreaks if the 8 in. soil temperatures average over 65° F during December, and there is no "soaking" rain during December. By soaking rain is meant quantities of precipitation greater than that required to bring the soil up to field capacity. The data do not suggest that such rains automatically render a season safe, but that if soil temperatures are marginal, such rains, particularly if spread over several days, will reduce the probability of widespread outbreaks. The commencement of the first toxic period in a season, as judged by liver damage in lambs grazing in the field, appeared to be preceded either by two or more periods when falls of rain greater than just a few points are accompanied by or immediately followed by two or more successive nights with grass-minimum temperatures of 54°F or over, or alternatively by a single prolonged group of high grass-minimum temperatures with rain. Also, the rain that was judged to initiate the first toxic period was itself accompanied by or immediately followed by two or more successive nights when grass-minimum temperatures were 54°F or higher. It appeared that where a period of high grass-minimum temperatures was accompanied by particularly heavy or continued rain, its effectiveness in either inducing toxicity or preparing pasture for toxicity was reduced. Periods of high grass-minimum temperatures with rain arise from weather disturbances accompanied by inflows of warm moist air. Meteorological conditions which result in this situation are described. They can generally be foreseen a day or two ahead.
Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantations on the east coast of Vancouver Island, British Columbia, were examined to determine the effect of animal feeding upon height growth.Length of internodes and evidence of past leader damage were recorded and cumulative average height-age growth curves compared for undamaged trees and for trees suffering various intensities of damage.The average reduction in tree height attributable to animal feeding in heavily browsed plantations varied from one-half to two feet over a period of 8 to 10 years. It is unlikely that either tree volume or quality at rotation age would be seriously affected.Exposed trees were browsed more heavily than those protected by vegetation or logging slash.
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