Browsing by Author "Visser, J. H."
Now showing 1 - 9 of 9
Results Per Page
- ItemConstruction of behaviourally anchored rating scales (BARS) for the measurement of managerial performance(AOSIS OpenJournals, 1989-05) Spangenberg, H. H.; Esterhuyse, J. J.; Visser, J. H.; Briedenhann, J. E.; Calitz, C. J.BARS were initially developed as indices of behavioural change and to ensure greater comparability of ratings from different raters. In this study, BARS were developed for a major producer-wholesaler company in the liquor industry to serve as an independent criterion in the validation of the company's assessment center, to assess the impact of development activities on the skill levels of assessment centre participants and as a diagnostic tool in identifying performance deficiencies. A step-by-step account of the four stages in the development of BARS is presented, together with examples of actual scales for the final steps.
- ItemThe determination of the homogeneity of a vitis vinifera L. cv. Cape riesling vineyard(South African Society for Enology and Viticulture, 1983) De la Harpe, A. C.; Visser, J. H.The value of Principal Component and Stepwise Discriminant analyses in selecting uniform plants for experimental purposes is discussed. Twenty seven variables were taken into account to establish the homogeniety (uniform plants) of 297 Vitis vinifera L. cv. Cape Riesling vines. A detailed study of the relationship and interrelationship of these variables resulted in 208 vines being selected as a uniform population. This selection provides the researcher with the possibility of using single vines as experimental units. However, it must be pointed out that Principal Component and Stepwise Discriminant analyses can only be used as an aid to normal statistical evaluation of experimental results and not as substitute for statistical experimental design.
- ItemDistribution of 14c-photosynthetate in the shoot of vitis vinifera L. cv cabernet sauvignon I. the effect of leaf position and developmental stage of the vine(South African Society for Enology and Viticulture, 1988) Hunter, J. J.; Visser, J. H.The distribution of photosynthetates, originating in leaves of different parts of the shoot of Vi tis vinifera L. cv Cabernet Sauvignon at berry set, pea size, veraison and ripeness stages, was investigated. Specific photosynthetic activity of the "CO,-treated leaves gradually decreased during the season. Photosynthetates were hoarded in the leaves at berry set, but were increasingly diverted to the bunches after that. The apical leaves displayed the Itlghes.t.photosynthesis. The leaves opposite and below the bunches accumulated very little photosynthetafes, especially from veraison to ripeness. Redistribution of photosynthetates among the basal, middle and apical leaves was generally very restricted at all stages. Multidirectional distribution from the site of application of 14CO, occurred at berry set stage, while from pea size to ripeness photosynthetates were mainly translocated basipetally. Highest accumulation in the bunches occurred at veraison, while the basal leaves were primarily used to nourish the bunch.
- ItemDistribution of 14C-photosynthetate in the shoot of vitis vinifera L. cv cabernet sauvignon II. the effect of partial defoliation(South African Society for Enology and Viticulture, 1988) Hunter, J. J.; Visser, J. H.The effect of partial defoliation of Vitis vinifera L. cv Cabernet Sauvignon on the distribution of photosynthetates, originating in leaves in different positions on the shoot at berry set, pea size, veraison and ripeness stages, was investigated. Partial defoliation (33% and 66%) resulted in a higher apparent photosynthetic effectivity for all the remaining leaves on the shoot. The pattern of distribution of photosynthetates would seem to stay the same between the defoliation treatments. The control vines were found to carry excess foliage. Optimal photosynthetic activity of all the leaves on the vine was therefore not reached.
- ItemThe effect of partial defoliation on growth characteristics of vitis vinifera L. cv. cabemet sauvignon I. vegetative growth(South African Society for Enology and Viticulture, 1990) Hunter, J. J.; Visser, J. H.The effect of partial defoliation of the whole canopy on vegetative growth of Vitis vinifera L. cv. Cabernet Sauvignon was investigated. Vegetative growth of vines followed the well-known pattern for 0%, 33% and 66% defoliation, i.e. an increase until veraison followed by a decline. Partial defoliation conducted from different developmental stages had no significant effect on leaf area and main shoot length at subsequent developmental stages. The earlier defoliation was applied, the more lateral shoot length and the number of lateral shoots increased, resulting in higher total shoot lengths but no significant differences in cane mass. Partial defoliation from veraison had no effect on lateral growth. Canopy density and relative humidity decreased, while sunlight penetration and windspeed increased in the canopy with partial defoliation. The improved canopy light environment facilitates improved photosynthetic efficiency of leaves as well as development and composition of grapes.
- ItemThe effect of partial defoliation, leaf position and developmental stage of the vine on leaf chlorophyll concentration in relation to the photosynthetic activity and light intensity in the canopy of Vitis vinifera L. cv. Cabernet Sauvignon(South African Society for Enology and Viticulture, 1989) Hunter, J. J.; Visser, J. H.The effect of partial defoliation and leaf position on leaf chlorophyll concentration in relation to the photosynthetic activity and light intensity in the canopy of Vitis vinifera L. cv. Cabernet Sauvignon was investigated at berry set, pea size, veraison and ripeness stages. The leaves of the severely defoliated vines appeared to contain the highest chlorophyll concentration. In general, chlorophyll a decreased as the leaves were situated progressively deeper into the canopy. No consistent relationship between chlorophyll concentration, light intensity and photosynthetic activity could be found for the different leaf positions. However, to obtain leaves that photosynthesize optimally, the amount and time of leaf removal in the grapevine canopy must be carefully planned.
- ItemThe effect of partial defoliation, leaf position and developmental stage of the vine on the photosynthetic activity of vitis vinifera L. cv cabernet sauvignon(South African Society for Enology and Viticulture, 1988) Hunter, J. J.; Visser, J. H.The effect of partial defoliation, leaf position and developmental stage of the vine on the photosynthesis, stomatal resistance and transpiration of Vitis vinifera L. cv Cabernet Sauvignon was investigated. Partially defoliated vines displayed a higher rate of photosynthesis, generally increasing with degree of defoliation. The highest photosynthetic rates were found for the apical leaves, while those of the leaves opposite and below the bunches were restricted. Generally, rate of photosynthesis declined as the season progressed. The course of transpiration rate and stomata! resistance correlated with that of the rate of photosynthesis. However, transpiration and photosynthesis correlated poorly in the case of the apical leaves. In general, photon flux density and relative humidity at the leaf surface increased with an increase in defoliation percentage for all leaf positions. Leaf temperature was not significantly affected by partial defoliation. The results of the investigation suggested that excess vegetative growth is detrimental to interior-canopy microclimate as well as the photosynthetic rate of the entire vine. Partial defoliation seemed to provide a means to reduce some of the deleterious effects of vigorous growth.
- ItemGrowth characteristics of vitis vinifera L. cv. Cape Riesling(South African Society for Enology and Viticulture, 1985) De la Harpe, A. C.; Visser, J. H.The effect of topping on the growth behaviour of Vitis vinifera L. cv. Cape Riesling vineyard was investigated. Shoot and leaf growth of both topped and untopped vines, can be described as sigmoidal. Shoot (cm) and leaf growth (cm') of the topped vines were significantly more than that of the untopped vines and are attributed to lateral shoot growth. Topping had no effect on bunch development. The development of skin, pulp and seed of both topped and untopped vines expressed as a percentage dry mass per berry can be described by a hyperbolic function for the skin, linear for the pulp and parabolic for the seed.
- ItemValidation of an assessment centre against BARS : an experience with performance related criteria(AOSIS OpenJournals, 1989-05) Spangenberg, H. H.; Esterhuyse, J. J.; Visser, J. H.; Briedenhann, J. E.; Calitz, C. J.The objective of this study is to determine the validity of a middle management assessment centre. Behaviourally Anchored Rating Scales were developed specifically for this purpose. The results testify to the validity of this assessment centre and lend support to the argument that assessment centres do indeed predict performance criteria (viz a viz potential/advancement criteria). The validity coefficients for the various dimensions are indicated.