G. A. Agenbag

Effect of seeding date on the performance of grasses and broadleaf species evaluated for cover crop management in two wine grape regions of South Africa.

A selection of species suitable for cover crop management in the different wine grape regions is required to enable more producers to apply this environment friendly practice in a sustainable manner as part of an integrated production strategy. The effect of seeding date on the dry matter production (DMP) and weed control efficacy of seven grasses and sixteen N-fixing broadleaf species, as well as varieties of three of these species, was determined. The decomposition rate of the mulches was measured to determine the mulch persistence of the different species. In the cooler climate of Stellenbosch (Coastal region) the Medicago species, subterranean clovers, pink Seradella (Omithopus sativa L. v. Emena) and three Vicia species did not compete effectively with the winter weeds if the weekly precipitation from mid-March to mid-May (autumn) exceeded 18 mm. The two oats varieties, as well as rye (Secale cereale L.) and triticale (Triticale v. Usgen 18), however, produced more than the five tons of dry matter deemed necessary for effective cover crop management if the precipitation exceeded 18 mm per week. The DMP of all the above-mentioned species was consistent between years at the warmer and arid Lutzville (Olifants River Valley) and indicated that these species could be considered for cover crop management in this region as well, if full surface irrigation of 18 mm per week could be applied for the first 10 weeks after sowing, followed by a fortnightly irrigation of 18 mm. Seeding date had a significant effect on DMP in the Stellenbosch region and showed similar trends in Lutzville. The study showed a highly significant correlation (r = 0.85, P < 0.0001) between the decomposition rate of the mulches and the initial amount of dry. matter present on the soil surface.

Multivariate assessment of environmental effects on hard red winter wheat. I. Principal-components analysis of yield and bread-making characteristics

The attributes of yield and bread-making quality of winter wheats produced in the Free State are subject to environmental effects. The result is a supply to the baking industry of flour of inconsistent quality, which in turn is detrimental to the market value of wheat. Various genetic and environmental factors may affect bread-making quality. In the first part of this study we demonstrated the magnitude of environmental and genetic factors, and used principal-components analysis to examine the underlying source of variability in the bread-making quality of winter wheat cultivars. Yield and protein concentration responded to environmental influences, whereas the dough-mixing requirement was primarily inherently determined. Variation in protein concentration accounted for variation in the mixing requirement of one cultivar and the SDS sedimentation volume of most cultivars.

Cover crop management in a chardonnay/99 Richter Vineyard in the Coastal Region, South Africa. 3. effect of different cover crops and cover crop management practices on organic matter and macro-nutrient content of a medium-textured soil

The trial was conducted over a period of 10 years (1993/94 to 2002/03) on a medium-textured soil in a Chardonnay/99 Richter vineyard near Stellenbosch (33°55’S, 18°52’E), which is situated in the Coastal wine grape region of the Western Cape, South Africa. Sixteen treatments, consisting of three cereals and five legumes, managed according to two cover crop management practices, were included. These treatments were compared to a control, in which no cover crop was sown and the weeds were controlled mechanically in the work row and chemically in the vine row from bud break to harvest (approximately the first week of February). A treatment in which no cover crop was sown and full-surface post-emergence chemical weed control was applied from before bud break to harvest (BB) (weedchem) was also included. After five seasons, the soil organic matter (SOM) content in the 0 to 300 mm soil layer increased in all the cover crop management treatments. In weedchem and in the control, SOM remained unchanged and decreased by 16% respectively. The SOM content in the 0 to 150 mm soil layer of the cover crop treatments was, with the exception of Vicia dasycarpa Ten. (grazing vetch), significantly higher than that of the mechanically-cultivated control after a period of 10 years. The SOM content in the 0 to 300 mm soil layer of Secale cereale L. v. Henog and the treatments in which the N-fixing cover crops were sown (with the exception of grazing vetch) was significantly higher than that of weedchem. The total inorganic N (TIN) concentration of the 0 to 150 mm soil layer in the BB treatments of the two Medicago species and Trifolium subterraneum L. v. Woogenellup, as measured for the 1996/97 season during full bloom of the grapevines, was significantly higher than that of the control, weedchem, and the treatments in which full-surface chemical control was applied after bud break (AB). The TIN concentration of the 0 to 600 mm soil layer in the AB treatment of a species, measured after harvest in 2002/03, tended to be higher than that of the BB treatment of that species. The applied treatments had no significant effect on the exchangeable K, Ca and Mg.

Cover crop management in a chardonnay/99 Richter Vineyard in the Coastal Region, South Africa. 2. effect of different cover crops and cover crop management practices on grapevine performance

The trial was conducted over a period of 10 years (1993/94 to 2002/03) on a medium textured soil in a Chardonnay/99 Richter vineyard near Stellenbosch (33°55’S, 18°52’E), situated in the Coastal Wine Grape Region of the Western Cape. Sixteen treatments, consisting of three grain species and five legumes, managed according to two cover crop management practices, were included. The one cover crop management practice consisted of cover crops being sown annually and full surface post-emergence chemical control being applied before bud break and when the berries reached pea size (BB). The other management practice consisted of cover crops being sown biennially and postemergence chemical control applied to the vine row before bud break and full surface when the berries reached pea size (AB). From 1999/2000 to 2002/03 the cover crops were sown annually, while the full surface post-emergence chemical control applied at the end of November was advanced to mid-October. These treatments were compared to a control, in which no cover crop was sown and the weeds were controlled mechanically in the work row and chemically in the vine row from bud break to harvest (approximately the first week of February). A treatment in which no cover crop was sown and full surface post-emergence chemical weed control was applied from before bud break to harvest (weedchem) was also included. During the 1994/95 season, the shoot mass of the two-year-old grapevines in the BB treatments was significantly higher than that of the control and the AB treatments. In the following season, the shoot mass and grape yield of the BB treatments was, with the exception of Vicia faba L. v. Fiord (faba bean) and Avena sativa L. v. Overberg, significantly higher than that of the control and weedchem. The grape yield of the control and AB treatments was significantly less than that of weedchem. Although significant differences in shoot mass (2000/01 and 2002/03) and grape yield (2002/03) were detected between treatments, no significant differences could be detected between the BB and AB treatments, with the exception of the shoot mass of Medicago scuttelata v. Kelson (‘Kelson’ medic). The mean petiole NO3-N concentration for the period 1994/95 to 1998/99 tended to be lower in the AB treatment of a cover crop species compared to that of the BB treatment of the same species. In the case of ‘Kelson’ medic (BB) the petiole NO3-N and juice N concentrations were significantly higher than that of the control and weedchem. The juice N concentration of the control and weedchem was significantly less than that of the faba bean treatments during 2000/01 and 2001/02, the Vicia dasycarpa Ten (grazing vetch) and ‘Kelson’ medic treatments during 2000/01, as well as that of Medicago truncatula Gaertn. (BB) and Trifolium subterraneum L. v. Woogenellup (BB) during the 2001/02 season. Wine quality did not differ between treatments.

Cover crop management in a Sauvignon Blanc-Ramsey vineyard in the semi-arid olifants River Valley, South Africa. 3. Effect of different cover crops and cover crop management practices on the Organic matter and macro-nutrient contents of a sandy soil

The trial was conducted over a period of ten years (1993/94 to 2002/03) on a sandy soil in a Sauvignon blanc/Ramsey vineyard near Lutzville (31o35’S, 18o52’E), situated in the semi-arid Olifants River Valley of the Western Cape. Fourteen treatments, consisting of three cereals and four legumes, managed according to two cover crop management practices, were included. One management practice consisted of cover crops which were sown annually. Full surface post-emergence chemical control was applied before bud break and again when the berries reached pea size (BB). The second management practice consisted of cover crops which were sown biennially. Post-emergence chemical control was applied to the vine row before bud break and full surface control was applied when the berries reached pea size (AB). From 1999/2000 to 2002/03 the cover crops were sown annually, while the full surface post-emergence control applied at the end of November (berries at pea size) was advanced to mid-October. Two treatments in which Avena sativa L. v. Saia (‘Saia’ oats) and Vicia dasycarpa Ten. (grazing vetch) were sown annually, controlled mechanically in the work row and chemically in the vine row from bud break to harvest (MC), were also applied. These treatments were compared to a control, in which no cover crop was sown and MC was applied. A treatment in which no cover crop was sown and BB was applied (weedchem), was also included. After five years (1997/98), the soil organic matter (SOM) in the 0-150 mm soil layer of the BB and AB treatments of grazing vetch was significantly higher than that of the control and weedchem. During March 2003, the SOM content in the 0-600 mm soil layer of grazing vetch (AB), as well as the 0-150 mm soil layer of Ornithopus sativus L. v. Emena (pink Seradella) (AB) and Secale cereale L. v. Henog (rye) (BB), was significantly higher than that of the control and weedchem. The total inorganic N concentration (TIN) of pink Seradella (BB) was the highest in the 0-150 mm soil layer during the full bloom stage of the grapevines in 1995/96 and significantly higher than that of the other treatments in the 150-300 mm soil layer. The TIN measured in the AB treatments of grazing vetch and pink Seradella as measured after the grapevine harvest (1995/96), was significantly higher than that of the control, weedchem and cereal treatments in the 0-300 mm and 0-150 mm soil layers, respectively. The TIN in the 0-150 mm soil layer of the legumes was, with the exception of pink Seradella (BB), significantly higher than that of the control, weedchem and the BB treatments of the cereals during March 2003. The TIN in the 150-300 mm soil layers of the AB treatments of pink Seradella and the two Medicago truncatula Gaertn. varieties, namely, Parabinga and Paraggio, was significantly higher than that of the control, weedchem and the grain treatments. Potassium concentrations in the 0-150 mm soil layer of the two pink Seradella treatments, the AB treatment of rye, Medicago truncatula Gaertn. v. Paraggio and grazing vetch, as well as the 150-300 mm soil layer of grazing vetch (BB) and pink Seradella (BB), were significantly higher than that of the control, weedchem and ‘Saia’ oats (MC) during March 1997.

The use of physiological parameters to identify drought tolerance in spring wheat cultivars

Wheat crops produced under dryland conditions in the winter rainfall region of South Africa often experience periods of water stress. It is, therefore, important to identify spring wheat cultivars that can withstand these conditions. The multitude of factors potentially involved in drought resistance make it unlikely that a single measurement will provide an all-encompassing test of drought tolerance. The aim of this study was to determine whether total ear water potential, relative water content (RWC), leaf diffusive resistance (LDR), transpiration rate and the accumulation of free proline could be used to distinguish between drought tolerant and drought sensitive spring wheat cultivars. The withholding of water and the use of polyethylene glycol (PEG) imposed stress at different physiological growth stages. It was shown in this study that these physiological parameters could be used to identify drought tolerance in spring wheat cultivars. Although genetic differences, as measured by the above-mentioned parameters, do exist between cultivars, the effect of water stress on plant growth and harvest data should also be taken into account in deciding whether these differences are of any commercial benefit.

Sources of variation for yield, protein content and hectolitre mass of spring wheat (Triticum aestivum L.) cultivars of the Western and Southern Cape

In the Western and Southern Cape the quality of wheat varies annually due to variable climatic conditions. This holds a commercial risk to the milling and baking industries in delivering the refined products to their respective clients. It is, therefore, important to classify cultivars and localities according to their ability to produce high quality bread wheat grain. In this study, similar production techniques were used to grow seven spring wheat cultivars at nine localities for the period 1992 to 1995. AMMI analyses were used to describe the effect of genotype, environment and their interaction on grain yield, kernel protein content and hectolitre mass. Environment was found to be by far the most important parameter of variance. No significant genotype × environment interaction was found for grain yield. Although cultivars differed in their yield potential, genotype as a main effect contributed only 1.3% to the variation in yield when compared to 90.7% for environment. Significant genotype × environme...

Cover Crop Management in a Sauvignon Blanc/Ramsey Vineyard in the Semi-Arid Olifants River Valley, South Africa. 2. Effect of Different Cover Crops and Cover Crop Management Practices on Grapevine Performance

The trial was conducted over a period of ten years (1993/94 to 2002/03) on a sandy soil in a Sauvignon blanc/ Ramsey vineyard near Lutzville (31o35’S, 18o52’E), situated in the semi-arid Olifants River Valley of the Western Cape. Fourteen treatments, consisting of three grain species and four legumes, managed according to two cover crop management practices, were included. One management practice consisted of cover crops which were sown annually and full surface, post-emergence chemical control which was applied before bud break and when the berries reached pea size (BB). The second management practice consisted of cover crops which were sown biennially. Post-emergence chemical control was applied to the vine row before bud break and full surface when the berries reached pea size (AB). From 1999/2000 to 2002/03 the cover crops were sown annually, while the full surface post-emergence control applied at the end of November was advanced to mid-October. Two treatments in which Avena sativa L. v. Saia (‘Saia’ oats) and Vicia dasycarpa Ten. (grazing vetch) were sown annually, controlled mechanically in the work row and chemically in the vine row from bud break to harvest (MC), were also applied. These treatments were compared to a control, in which no cover crop was sown and MC was applied. A treatment in which no cover crop was sown and BB was applied (weedchem), was also included. During the third growing season of the vines (1994/95), the grapevine shoot mass of the BB treatments of grazing vetch and Medicago truncatula Gaertn. v. Paraggio (‘Paraggio’ medic) was significantly more than that of the AB and MC treatments, with the exception of Secale cereale L. v. Henog (AB) and grazing vetch (MC). The first harvest (1994/95) from the grapevines in the BB treatments was significantly higher than that of weedchem and the MC treatments. The grape yield of the BB treatments, grazing vetch (AB) and Ornithopus sativus L. v. Emena (pink Seradella) (AB) was significantly more than that of weedchem and the control during the 1997/98 season. The NO3-N concentration in the leaf petioles in all the cover crop treatments was, with the exception of the AB treatments of rye, M. truncatula Gaertn. v. Parabinga (‘Parabinga’ medic) and grazing vetch, significantly higher than that in weedchem and the control, as measured during the 1994/95 season. The NO3-N concentration in the leaf petioles of the BB and AB treatment of a species differed significantly. The N concentration in the juice of the cover crop treatments during the 1995/96 season was, with the exception of ‘Saia’ oats (MC) and ‘Parabinga’ medic (AB), significantly higher than that of weedchem and the control. During the 1998/99 season, the N concentration of the juice in the BB and AB treatments of grazing vetch and pink Seradella was significantly higher than that of the MC treatments, two rye treatments, weedchem and the AB treatments of the other cover crops. The concentration of Ca in the juice of the cover crop treatments was, with the exception of the pink Seradella treatments, significantly higher than that of weedchem and the control. Wine quality did not differ between treatments.

Anatomical and compositional changes during fruit development of ‘Galia’ melons

‘Galia’ melons were grown under controlled conditions and pruned to bear two fruits with 19 leaves per plant. Leaves and fruits were sampled and analysed at eight different stages. Pericarp cell division and enlargement occurred during the first week after anthesis but only cell enlargement was responsible for fruit growth thereafter. An increase in fruit-peel surface during the first 3 days after anthesis (DAA) was due mainly to epidermal cell division. During the following 11 days fruit-peel area increased due to increases in epidermal cell size. At 14 DAA no further epidermal cell enlargement occurred, probably due to an increase in cuticle thickness. After this stage fruit peel surface increased due to cracks in the epidermal layer which preceded and probably initiated lenticel development. In leaves adjacent to developing fruit, a reduction in starch occurred during the last week of fruit development, coinciding with sharp increases in glucose, fructose and sucrose levels and an increase in total fruit-flesh sucrose from 50.4 g to 111.6 g per fruit, illustrating the importance not to harvest prematurely.

Growth, yield and grain protein content of wheat (Triticum aestivum L.) in response to nitrogen fertiliser rates, crop rotation and soil tillage

Soil tillage affects both the profitability and sustainability of cropping systems. Minimum- and no-tillage systems are promoted because research has shown that these systems may reduce production costs and improve biological sustainability when compared to conventional systems, in which mouldboard and disc ploughs are used. However, responses to different tillage systems may differ for different crops as well as different soil and climatic conditions. This long-term study, conducted under a Mediterranean-type climate, showed that no-tillage systems can be used successfully to produce spring-type wheat crops in sustainable crop rotation systems under rain-fed conditions in the Swartland wheat-producing area of the Western Cape province of South Africa. Higher wheat yields when wheat is grown in a crop rotation system compared to a monoculture system can be ascribed to improved soil organic carbon and nitrogen (N) contents, which result in more plant-available mineral N and hence more vigorous crop growth. Grain yields of wheat responded positively to increased N application rates and the results suggest that application rates of more than 100 kg ha−1 should be considered where minimum and no-tillage are practised. Higher N application rates resulted in higher grain protein and hence improved bread-making quality of the wheat.