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/Ramseyvineyard 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 managementpractices, were included. One management practice consisted of cover crops which were sown annually. Full surfacepost-emergence chemical control was applied before bud break and again when the berries reached pea size (BB). Thesecond management practice consisted of cover crops which were sown biennially. Post-emergence chemical controlwas 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 controlapplied at the end of November (berries at pea size) was advanced to mid-October. Two treatments in which Avenasativa L. v. Saia (‘Saia’ oats) and Vicia dasycarpa Ten. (grazing vetch) were sown annually, controlled mechanically inthe work row and chemically in the vine row from bud break to harvest (MC), were also applied. These treatmentswere compared to a control, in which no cover crop was sown and MC was applied. A treatment in which no covercrop 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 ofthe 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 grapevinesin 1995/96 and significantly higher than that of the other treatments in the 150-300 mm soil layer. The TIN measuredin the AB treatments of grazing vetch and pink Seradella as measured after the grapevine harvest (1995/96), wassignificantly higher than that of the control, weedchem and cereal treatments in the 0-300 mm and 0-150 mm soillayers, 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 March2003. The TIN in the 150-300 mm soil layers of the AB treatments of pink Seradella and the two Medicago truncatulaGaertn. varieties, namely, Parabinga and Paraggio, was significantly higher than that of the control, weedchem andthe grain treatments. Potassium concentrations in the 0-150 mm soil layer of the two pink Seradella treatments, theAB treatment of rye, Medicago truncatula Gaertn. v. Paraggio and grazing vetch, as well as the 150-300 mm soil layerof grazing vetch (BB) and pink Seradella (BB), were significantly higher than that of the control, weedchem and ‘Saia’oats (MC) during March 1997

Cover crop management in a Sauvignon blanc/Ramsey vineyard in the semiarid Olifants River Valley, South Africa. 1. Effect of management practices on selected grass and broadleaf species

This trial was conducted over a period of ten years on a sandy soil in a Sauvignon blanc/Ramsey vineyard in Lutzville (31°35’S, 18°52’E), situated in the semi-arid Olifants River Valley of the Western Cape. Twenty-three treatments were applied. Eight cover crop species that received the same amount of fertilizer were controlled chemically at the end of August or at the end of November. Two treatments were also applied in which Avena sativa L. v. Saia (‘Saia’ oats) and Vicia dasycarpa Ten. (grazing vetch) were controlled mechanically during bud break.  In addition to these eighteen treatments, two fertiliser application rates were applied to ‘Saia’ oats and grazing vetch. A mechanically cultivated control in which no cover crop was sown was included in the trial. Secale cereale L v. Henog and Ornithopus sativus L. v. Emena produced, on average, the highest amount of dry matter at the end of August (3.29 t/ha and 3.06 t/ha, respectively) after receiving on average 278 mm of water, of which 172 mm was supplied by means of a micro-sprinkler irrigation system. The average dry matter produced by Medicago truncatula Gaertn. v. Paraggio and ‘Saia’ oats at the end of August was not significantly lower than that of the firstmentioned two species. Under conditions of this experiment, it seemed that P and K at a concentration of 10 mg/kg and 78 mg/kg, respectively, in the top 300 mm soil layer supplied the needs of grazing vetch. Saia oats performed poorly unless 30 kg P, 30 kg K and 42 kg N were applied during establishment and the early growing phase. All the species, except M. truncatula Gaertn v. Parabinga, produced additional fibre from September to the end of November following a dry winter (rain and irrigation totaling 201 mm), while none produced additional fibre if the water supply was luxurious up to the end of August (rain and irrigation totaling 364 mm). The cover crops did not produce enough seeds to re-establish successfully over a period of five years. It will, however, be possible to reduce the seeding density of grazing vetch (40% after two seasons) and the two M. truncatula varieties (20% after five seasons) if the species were left to ripen their seeds

Cover Crop Management in a Chardonnay/99 Richter Vineyard in the Coastal Wine Grape Region, South Africa. 1. Effect of Two Management Practices on Selected Grass and Broadleaf Species

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 Regionof the Western Cape. Sixteen treatments, consisting of three grain species and five N-fixing broadleaf species managed according to two cover crop management practices, were included. These treatments were compared to a control treatment, in which no cover crop was sown and the weeds were controlled mechanically in the work row and chemically in the vine row from the first week of September to the end of March (grapevine growing season).  A treatment in which no cover crop was sown and full surface post-emergence chemical control was applied during the grapevine growing season was also included. The different weed control actions were carried out during the first week of September and/or at the end of November, as well as mid October (1999/00 to 2002/03). Secale cereale L. v. Henog (rye), Avena sativa L. v. Overberg (‘Overberg’ oats), Avena strigosa L. v. Saia (‘Saia’ oats) and Vicia faba L. v. Fiord [only if sown annually and controlled chemically before bud break (BB)], showed the ability to produce,on average, significantly more dry matter during winter than the weeds in the region. The dry matter production of all the cover crops increased from the end of August to the end of November if left to complete their life cycles, with the exception of rye and ‘Overberg’ oats sown in early April. None of the cover crop species were able to reestablish successfully. Continuous effective suppression of winter growing weeds (less than 20% of the weed stand in the control) was achieved with ‘Overberg’ oats (BB) and ‘Saia’ oats (BB), while total suppression was achieved for six and five of the 10 years, respectively. Effective, long-term control of the summer growing weeds was obtained with rye (BB), ‘Overberg’ oats (BB) and ‘Saia’ oats (BB)

Effect of Seeding Date on the Performance of Grasses and Broadleaf Species Evaluated for Cover Crop Management in the Breede River Valley Wine Grape Region of South Africa

The trial was conducted over a period of two years on a medium-textured soil near Robertson (33°50’S, 19°54’E),situated in the Breede River Valley of the Western Cape. The effect of seeding date on the dry matter production(DMP) and weed control efficacy of eight grasses and sixteen N-fixing broadleaf species, as well as varieties of threeof these species, were determined. The decomposition rate of the surface mulches during summer (from the end ofAugust to the end of January) was measured to determine the persistence of the fibre of the different species.Seeding date had a significant effect on most of the species. Triticale v. Usgen 18 (triticale), Avena sativa L. v.Overberg (‘Overberg’ oats), Avena strigosa L. v. Saia (‘Saia’ oats) and Secale cereale L. v. Henog (rye) effectivelysuppressed the winter-growing weeds of the region and produced more than the five tons of dry matter per hectaredeemed necessary for effective cover crop management with a grass species. These species produced the highestamount of dry matter if sown in early April (mid-autumn). Vicia faba L. v. Fiord (faba bean) and Medicago truncatulav. Paraggio (‘Paraggio’ medic) controlled the winter-growing weeds acceptably, while producing more thanthe six tons of dry matter per hectare suggested to be necessary for the prevention of erosion in most vineyard soils.Vicia dasycarpa Ten. (grazing vetch) suppressed the winter-growing weeds acceptably. Although these legumes didnot produce more than the eight tons of dry matter per hectare deemed necessary for effective control of summergrowing weeds under intensive full-surface irrigation, they should still be considered for cover crop managementon soils with a low organic matter content in the region, because of their ability to supply nitrogen to the grapevines.A highly significant correlation was found between the decomposition rate of the surface mulch and the initialamount of dry matter present on the soil surface

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 WesternCape. Fourteen treatments, consisting of three grain species and four legumes, managed according to two cover cropmanagement practices, were included. One management practice consisted of cover crops which were sown annuallyand full surface, post-emergence chemical control which was applied before bud break and when the berries reachedpea size (BB). The second management practice consisted of cover crops which were sown biennially. Post-emergencechemical 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 controlapplied 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 andchemically in the vine row from bud break to harvest (MC), were also applied. These treatments were compared toa control, in which no cover crop was sown and MC was applied. A treatment in which no cover crop was sown andBB was applied (weedchem), was also included. During the third growing season of the vines (1994/95), the grapevineshoot mass of the BB treatments of grazing vetch and Medicago truncatula Gaertn. v. Paraggio (‘Paraggio’ medic) wassignificantly more than that of the AB and MC treatments, with the exception of Secale cereale L. v. Henog (AB) andgrazing vetch (MC). The first harvest (1994/95) from the grapevines in the BB treatments was significantly higher thanthat of weedchem and the MC treatments. The grape yield of the BB treatments, grazing vetch (AB) and Ornithopussativus L. v. Emena (pink Seradella) (AB) was significantly more than that of weedchem and the control during the1997/98 season. The NO3-N concentration in the leaf petioles in all the cover crop treatments was, with the exceptionof the AB treatments of rye, M. truncatula Gaertn. v. Parabinga (‘Parabinga’ medic) and grazing vetch, significantlyhigher than that in weedchem and the control, as measured during the 1994/95 season. The NO3-N concentration inthe leaf petioles of the BB and AB treatment of a species differed significantly. The N concentration in the juice of thecover 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 ofthe juice in the BB and AB treatments of grazing vetch and pink Seradella was significantly higher than that of theMC treatments, two rye treatments, weedchem and the AB treatments of the other cover crops. The concentrationof Ca in the juice of the cover crop treatments was, with the exception of the pink Seradella treatments, significantlyhigher than that of weedchem and the control. Wine quality did not differ between treatments

Effects of Liming to Near-neutral pH on Vitis vinifera L.

Wine grape vines are sensitive to soil pH and liming. The effects of pre-plant liming at rates sufficient to promoteaverage soil pH levels (1M KCl) of 5.05 (unlimed, treatment L0), 5.64 (L1) and 6.56 (L2) in two wine grape (scion)varieties and four rootstocks five years after planting were investigated over six seasons in a factorial field trial atStellenbosch. Yields tended to decrease in the sequence: L0 > L1 > L2, and were significantly (P = 0.05) lower in L2than in L0. Conversely, cane masses increased progressively with lime application rate, with L1 exceeding L0 by11.0% and L2 exceeding L1 by 13.0%. These increases were significant. Compared to L0, liming decreased the ratioof yield to cane mass by 13.6% in L1 and 28.8% in L2, but increased Ca:Mg ratios in the soil and petioles. Winequality was significantly better from L0 than L2. Petiole N concentrations were above normal in all treatments.Suppressed yields and wine quality in the limed treatments were attributed to a lime-induced imbalance betweenvegetative and reproductive growth, possibly exacerbated by increased Ca:Mg ratios and excess nitrogen

Effects of Rootstock on Grapevine Performance, Petiole and Must Composition, and Overall Wine Score of Vitis vinifera cv. Chardonnay and Pinot noir

Characteristics of Chardonnay and Pinot noir vines on Richter 99 (99R), Richter 110 (110R), Ruggeri 140 (140Ru)and SO4 rootstocks were assessed over six consecutive seasons in a factorial field trial on an Avalon soil in Stellenboschthat had been limed to pH 5.75 (1M KCl). Ruggeri 140 promoted the highest cane mass (vigour), highest petioleand must nitrogen (N), lowest ratio of yield to cane mass, and lowest overall wine quality. The lowest cane mass andhighest wine quality were produced by vines on 110R. Petiole N, phosphorus (P), calcium (Ca) and magnesium (Mg),and must N and Ca, were also lower for vines on 110R than for those on 140Ru

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 postemergencechemical 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-emergencechemical 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-oldgrapevines 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 significantdifferences 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 thatof 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 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 aChardonnay/99 Richter vineyard near Stellenbosch (33°55’S, 18°52’E), which is situated in the Coastal wine graperegion of the Western Cape, South Africa. Sixteen treatments, consisting of three cereals and five legumes, managedaccording 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 inthe vine row from bud break to harvest (approximately the first week of February). A treatment in which no covercrop was sown and full-surface post-emergence chemical weed control was applied from before bud break toharvest (BB) (weedchem) was also included. After five seasons, the soil organic matter (SOM) content in the 0 to300 mm soil layer increased in all the cover crop management treatments. In weedchem and in the control, SOMremained unchanged and decreased by 16% respectively. The SOM content in the 0 to 150 mm soil layer of thecover crop treatments was, with the exception of Vicia dasycarpa Ten. (grazing vetch), significantly higher than thatof the mechanically-cultivated control after a period of 10 years. The SOM content in the 0 to 300 mm soil layer ofSecale cereale L. v. Henog and the treatments in which the N-fixing cover crops were sown (with the exception ofgrazing vetch) was significantly higher than that of weedchem. The total inorganic N (TIN) concentration of the 0to 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 thanthat of the control, weedchem, and the treatments in which full-surface chemical control was applied after budbreak (AB). The TIN concentration of the 0 to 600 mm soil layer in the AB treatment of a species, measured afterharvest in 2002/03, tended to be higher than that of the BB treatment of that species. The applied treatments hadno significant effect on the exchangeable K, Ca and Mg

The Occurrence and Infectivity of Arbuscular Mycorrhizal Fungi in Inoculated and Uninoculated Rhizosphere Soils of Two-year-old Commercial Grapevines

Arbuscular mycorrhizal (AM) fungal populations present in the rhizosphere of vine roots in the vineyards of a commercial farm in the Stellenbosch Region were investigated using microscopic analyses. AM root colonisation levels of between 70% and 90% were found in both grapevine roots that were previously artificially inoculated with commercial AM inocula, and in uninoculated (control) grapevine roots. The AM fungal isolates in the rhizosphere soil, identified using morphological criteria, belonged to the genera Acaulospora, Gigaspora, Glomus, Sclerocystis and Scutellospora.  The majority of species found was not present in the commercial inocula and was either indigenous to the vineyard or originated from the nursery where the vines were obtained. Isolates of Glomus and Acaulospora appeared to be the most abundant. The AM fungal species occurred at a soil phosphorus (P) concentration of up to 80 mg/kg P and a soil pH (KCl) that ranged between 5.63 and 6.10. Total spore counts ranged between 1 000 and 3 779 spores/100 g dry soil. In accordance with literature, lower spore concentrations were recorded for the heavier soil types with no cover crop system, compared with the sandy soil type on which cover crops were sown annually