Browsing by Author "Weber, H. W."

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    Cardiomyopathy in crowded rabbits : a preliminary report
    (Health & Medical Publishing Group, 1973) Weber, H. W.; Van Der Walt, J. J.
    Rabbits were crowded 4 to a cage for 2 wk, then released for 1 wk, crowded again for 1 wk, and so on. Of 44 rabbits subjected to intermittent crowding only 9 survived longer than 10 mth, 20 died during the 1st month and 15 died between the 2nd and 9th mth of the experiment. Autopsy findings were indicative of heart failure. Light microscopical sections of the myocardium showed myocytolysis, interstitial edema, and an increased amount of acid mucopolysaccharides in rabbits surviving for 2 wk and more. Some rabbits surviving longer than 2 wk had in addition coagulative myocardial necrosis. The accumulations of acid mucopolysaccharides apparently were unrelated to necrotic foci. Longtime survivors frequently showed myocardial fibrosis and endocardial fibro elastosis, as well as basophilic degeneration of myocardial fibers. The lesions observed were similar to those described in idiopathic endomyocardiopathy in Southern Africa. Therefore, the rabbit may be of some value for research in cardiomyopathies.
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    The effect of conventional and minimum tillage practices on some soil properties in a dryland vineyard
    (South African Society for Enology and Viticulture, 1980) Van Huyssteen, L.; Weber, H. W.
    Preliminary results of a long-term viticultural tillage experiment comprising two groups of treatments, are reported. These groups are (i) a group of "minimum" tillage practices having received no mechanical soil tillage at all, and (ii) a group of "conventional" tillage treatments according to long-established local practices by disc-harrow. The "minimum" group consists of: (a) a permanent straw mulch cover, (b) chemical weed control, and ( c) a permanent cover of indigenous weeds frequently cut by a bush-cutter. The "conventional" group consists of: (a) deep and (b) shallow trench furrow systems, and (c) the locally customary "clean cultivation" system. A comprehensive investigation into the changes of sleeted soil properties after a period of eight years revealed significant differences between properties of the soil under minimum tillage (group (i)) and under clean cultivation (group (ii)). Soil parameters, such as pore volume distribution, compaction indices, activity of micro-organisms and availability of plant nutrients, were found to be more favourable in some minimum tillage treatments than on the conventionally tilled plots.
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    The effect of selected minimum and conventional tillage practices in vineyard cultivation on vine performance
    (South African Society for Enology and Viticulture, 1980) Van Huyssteen, L.; Weber, H. W.
    A long-term vineyard cultivation experiment, comprising six tillage treatments which represent a "conventional'' cultivation group as well as a group of "minimum" tillage practices, was started in 1968 at Nietvoorbij Experimental Farm of the OVRI, Stellenbosch. The first group included (i) the "shallow trench furrow", (ii) the "deep trench furrow", and (iii) the locally customary "clean cultivation" systems, and the second group comprised (i) a straw mulch cover on the soil surface, (ii) chemical weed elimination by herbicides, and (iii) a permanent "sward" of indigenous weeds. Distinct differences in vine performance between treatments were found. The general appearance, nutritional status and some important growth parameters of vines, as well as yield and quality of grapes, musts and wines from the straw mulch and herbicide treated (minimum) plots were markedly superior to the same properties of vines, grapes and wines from the conventionally tilled plots and the sward treatment, the latter due to competition of weeds for water and nutrients. However, a tentative economical analysis showed that the deep furrow trenching gave a sufficiently high yield to merit further consideration, although it could not reach the economical performance of the herbicide treatment.
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    The effect of various supplementary irrigation treatments on plant and soil moisture relationships in a vineyard (vitis vinif era var. chenin blanc)
    (South African Society for Enology and Viticulture, 1981) Van Zyl, J. L.; Weber, H. W.
    In a field plot trial with grape vines planted on a high potential soil, the soil moisture status on different irrigation treatment plots was compared with that of a dryland control. Soil moisture budgeting was based on physical soil properties and root distribution patterns before treatments commenced. A maximum concentration of roots occurred at the 300-450 mm depth zone, while approximately 90 per cent of the total number of roots was found above 900 mm. Tensiometric readings of soil moisture potential, supplemented by electrometric resistance readings from gypsum blocks, indicated complete depletion between veraison and harvesting of the total available moisture on dryland plots. Despite this severe moisture stress as illustrated by chrono-isopletes, a reasonably good grape yield was still produced by the dryland vines, indicating either exceptional drought resistance or the uptake of water from extraneous sources. Supplementary irrigations greatly improved soil moisture conditions during the important growth stages of (a) flowering and fruit set, (b) green berry stage and (c) veraison. Moisture depletion patterns changed markedly as the season progressed from November to January, and as naturally stored rain water became depleted. In contrast to the absorption pattern in November, the fastest rate of water loss occurred in the deepest root zones during January, because of unsaturated moisture flow into the dry partly decomposed parent material. The apparently unproductive subsoil might act as a large natural reservoir for superfluous winter rain, which in summer becomes available to the vines through unsaturated upward flow into the root zone. Determination of leaf water potential showed unexpectedly high values at night (minima of -283kPa) in plants growing in soil of which the major part was dried below wilting point. Vines were thus able to regain turgidity at night. Crop factors for use with the American Class A-pan for scheduling irrigations were calculated. Crop factors were low (November to February = 0,20-0,30), and again emphasised the ability of vines to use water frugally. Crop factors were strongly dependent upon soil moisture conditions. Empirical coefficients for use in the Blaney-Criddle formula are also presented.
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    Soil moisture conservation in dryland viticulture as affected by conventional and minimum tillage practices
    (South African Society for Enology and Viticulture, 1980) Van Huyssteen, L.; Weber, H. W.
    The effect of conventional clean cultivation, a straw mulch, chemical weed control and a grass sward on the soil moisture regime in a dryland vineyard was investigated. The results demonstrate that both a straw mulch and chemical weed control were very effective ju conserving winter-stored soil moisture until mid- or even late summer to support the vines during the almost rainless growing season. Further, it appeared that a mere loosening of the soil surface periodically by way of clean cultivation cannot conserve soil moisture effectively; it may, on the contrary, promote evaporation in the top-soil layers, especialzy when done after rain. On the other hand, an undisturbed soil surface, as in the case of chemical weed control, acts as a mulch in itself after the surface layer has dried out, thus reducing evaporation. Even under conditions of frequent rainfall, as during the first part of 1976/77 season, the straw mulch cover treatment was still superior to all other treatments in conserving soil moisture.