Browsing by Author "Saayman, D."

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    The effect of fertilisation on the performance of Barlinka table grapes on sandy soil, Hex River Valley
    (South African Society for Enology and Viticulture, 1995) Saayman, D.; Lambrechts, J. J. N.
    The response of Barlinka table grapes on grayish, sandy soil to irrigation-applied N fertilisation levels, patterns of N application, crop load and stock P and K fertilisation, were evaluated over a 12-year period in the Hex River Valley. Under the conditions of the trial, an N level of about 100 kg ha-1 appeared to be optimum for shoot growth and grape quality. Bunch and crop mass benefited from increased N levels, apparently due to better berry set. Increased N levels also appeared to preserve greenness of bunch stems better during cold storage but N levels higher than 105-120 kg ha-' reduced colour and sugar content of berries. Applying 67% of total seasonal N during the pre-bloom to veraison period and the rest after harvest, as against a 50:50 distribution, had a slight, positive effect on shoot growth and bunch size, again apparently caused by better berry set. Indications of a small, positive response of shoot growth to stock P fertilisation were obtained. Potassium applied in this manner was found to be ineffective due to leaching and regular irrigation-applied K fertilisation had to be adopted. Increased crop load had a marked negative effect on shoot growth and grape quality, in the latter case comparable in magnitude to that of too high N levels. A balanced crop load of 22 bunches per vine with a shoot mass of 1,822 kg, was calculated for this trial, but a crop load of 18-19 bunches per vine appeared to be the maximum that still ensured the best quality.
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    The effect of irrigation system and crop load on the vigour of Barlinka table grapes on a sandy soil, Hex River Valley
    (South African Society for Enology and Viticulture, 1995) Saayman, D.; Lambrechts, J. J. N.
    The effect of drip and micro-sprinkler irrigation, as well as crop load, on the vigour of Barlinka table grapes was studied in a field trial in the Hex River Valley over a 12-year period. Regulating soil water by means of tensiometers alone proved to be ineffective in the case of drippers, causing reduced vigour compared to micro-sprinklers. This could be rectified by using a fixed 2-day schedule and evaporation data. Increased bunch numbers per vine were found to have a pronounced and consistently depressive effect on shoot mass. It was proposed that an approach be followed of deciding on an acceptable vigour and then allocating bunches accordingly, using a formula developed from data obtained in this experiment. Significant seasonal variation in vigour caused by crop load and indications of similar effects due to calculated water deficits, were obtained. Combining these two factors in a regression model, shoot mass data were recalculated, revealing no consistent effect of irrigation systems on shoot growth. Mean seasonal water requirements were found to be 569 mm for micro-sprinklers and 411 mm for drippers. The more than 25% saving with drippers was mainly due to a reduced wetted soil volume.
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    Nitrogen mineralisation in vineyard soils of the Western Cape as affected by soil management practices
    (South African Society for Enology and Viticulture, 1995) Raath, P. J.; Saayman, D.
    Soil management practices like ridging, liming and irrigation are expected to affect the ability of microorganisms to mineralise plant residues in the soil through their effects on water regime, temperature, pH, organic C and total N contents. Investigations into seasonal changes in the mineral N contents of typical vineyard soils, as affected by these practices, were initiated during 1991 in existing vineyard trials. Soil water, soil temperature and mineral N were measured at regular intervals over two growing seasons. Ridged soil showed higher N release than non-ridged soil during winter, resulting in higher mineral N content at budburst. The effect of liming on microbial activity probably abated after 5 years because no difference in mineral N contents were obtained between soils of different pH. Irrigation showed no effect on N release, probably because of treatment design. Decreases in mineral N content during the growing season in soils from all the trials could not always be attributed to uptake by grapevines or to decreases in potentially mineralisable N contents and microbial activity.
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    The possible cause of red leaf disease and its effect on barlinka table grapes
    (South African Society for Enology and Viticulture, 1993) Saayman, D.; Lambrechts, J. J. N.
    The so-called red leaf (RL) phenomenon of Barlinka table grapes was investigated in the Hex River Valley, De Doorns. The symptoms of RL were found to resemble those of grapevine leafroll (GLR) disease to a certain extent, but also differed markedly from GLR in that initial reddening occurs in veins of apical leaves, with the typical downward curling of affected leaves not a distinctive feature. Like GLR, RL induces uneven and retarded ripening, small and shot berries, without colour in extreme cases, making the grapes worthless for export. Vine vigour is also seriously reduced. The cause of RL was found not to be a Ca deficiency as previously postulated and generally accepted. Foliar and soil applied Ca proved ineffective. Reciprocal grafting of red leaf-affected and heat-treated plant material showed that RL is associated with plant-transmissible pathogens, probably similar or belonging to viruses associated with GLR.