Browsing by Author "Moffat, Emma Georgina"

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    Mulching and tillage with compost to improve poor performing grapevines
    (Stellenbosch : Stellenbosch University, 2017-12) Moffat, Emma Georgina; Myburgh, P. A.; Strever, A. E.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
    ENGLISH SUMMARY: The study explored two strategies for improvement of grapevine performance. The first aim was to assess varying levels of compost mulch thickness and the effects thereof on soil water content and grapevine performance as well as to determine whether mulching can be recommended as a watersaving practice under the given conditions. The second aim was to investigate the effect of incorporating organic matter during the root pruning action and with a furrow plough, on the soil environment and grapevine performance. Where spatial variability in sloped or terraced vineyards is a concern, application of compost as a mulch to the grapevine row is impractical. A clear understanding of whether or not incorporating compost proves to have substantial benefits to soil water infiltration and retention, as well as grapevine performance, would be of value to the wine industry. Two methods of organic matter incorporation were compared, namely the furrow plough and deep tillage or root pruning. In the first experiment, compost mulch was applied on the grapevine row at varying thicknesses in a Shiraz/101-14 Mgt vineyard near Stellenbosch. Results showed that the application of compost mulch to a thickness of 16 cm had no effect on soil water content to a depth of 90 cm compared to the bare soil. While greater fluctuations in soil water content occurred in the 0-30 cm layer, the treatments did not differ with respect to soil water content over the two seasons. However, water infiltration rate increased with mulch thickness, i.e. the highest infiltration rate was observed in the soils under the thicker mulches. Nevertheless, the thicker mulches, i.e. 8 cm and 16 cm, appeared to intercept rainfall when relatively small events occurred. Under the prevailing conditions, the mulch was not effective in maintaining a higher soil water content on the grapevine row compared to bare soil. Grapevine water constraints were also not affected by compost mulch, regardless of the thickness. However, vegetative growth and yield responded positively to mulch thickness over the two seasons. Since water constraints did not differ in response to mulch thickness, improved water uptake was not considered to have contributed to the improved growth and yield. Fine root development observed in the shallow soil layers under the mulches could have contributed to the growth response by allowing for improved nutrient absorption. The mulch had weathered substantially after two years, which was attributed to the maturity of the compost and the quantity of fine material. In the second experiment, compost was incorporated using a furrow plough during the root pruning action, and compared to a no-till and no compost control, as well as root pruning without compost. The treatments were applied in every, and in alternate rows in a terraced Pinotage/R110 vineyard near Stellenbosch. Compost incorporation by means of the furrow plough and root pruning, increased water infiltration rate compared to the control. Root pruning without compost also tended to increase infiltration rate. Higher infiltration rates are expected to reduce water loss by runoff and increase in the amount of water entering the soil. However, the tillage and compost treatments had no effect on the soil water content on the grapevine row. It would seem that there was limited lateral flow of water from the work row to the grapevine row. After two years, the furrow plough with compost and root pruning with and without compost reduced penetration resistance up to 15 cm and 45 cm, respectively. The lower penetration resistance in the soil where compost was incorporated using the furrow plough could be attributed to a slightly higher soil water content in that layer where the compost was concentrated. The penetration resistance in the soil of the control exceeded the 2000 kPa threshold for inhibited root growth at a depth of 12 cm. The soil loosening action of the root pruning with compost is expected to allow for improved root development to a greater depth than the furrow plough treatment. However, the furrow plough treatment may have encouraged root development between the tractor wheel tacks to a depth of 15 to 20 cm. Root pruning per se had no effect on the soil chemical status, but decreased compaction. Where compost was added, the soil pH increased, probably due to the high amount of calcium in the compost and the dissolution of organic acids present in the organic material. The compost also tended to increase magnesium, potassium and sodium as well as organic carbon and phosphorus in the soil, particularly in the shallow layers. The potassium and phosphorus could be a source of nutrients to the grapevines, while the organic carbon influences the accumulation of soil organic matter. Although the amount of sodium in the soil increased, the extractable sodium percentage was in fact reduced in the 0-15 cm soil layer, due to the high amount of calcium. The extractable sodium percentage was also well below the threshold where sodicity problems would be expected. Under the prevailing conditions, root pruning did not seem to have a positive effect on grapevine vegetative growth and yield. Rainfall during the study was appreciably lower than the long term mean, particularly in 2015. As a result of dry soil conditions the degree of root regeneration in the loosened soil and the subsequent grapevine responses may have been affected. In contrast, where compost was incorporated during the root pruning action, growth and yield increased over two consecutive seasons. Likewise, where compost was incorporated in furrows, it also had a positive effect on growth and yield. It appeared that root pruning in every row with compost did not provide significant additional benefits to growth and yield compared to the root pruning in alternate rows with compost. Apart from the slightly higher pH and lower colour in the wines of the compost treatments in the first year, juice and wine quality characteristics were not affected by any of the tillage or compost treatments. The higher potassium content in the soils measured two years after the compost was applied appeared to have had no effect on juice and wine quality. Cover crop growth also responded positively to the addition of compost. It is interesting to note that the enhanced cover crop performance did not appear to compete with the grapevines. Decomposition and mineralisation of the cover crop residue in the vineyard would be expected to further improve organic matter and nutrient accumulation in the soils where cover crop dry matter production was high.