Mulching and tillage with compost to improve poor performing grapevines

[摘要] ENGLISH SUMMARY: The study explored two strategies for improvement of grapevine performance. The first aim was toassess varying levels of compost mulch thickness and the effects thereof on soil water content andgrapevine performance as well as to determine whether mulching can be recommended as a watersavingpractice under the given conditions. The second aim was to investigate the effect ofincorporating organic matter during the root pruning action and with a furrow plough, on the soilenvironment and grapevine performance. Where spatial variability in sloped or terraced vineyards isa concern, application of compost as a mulch to the grapevine row is impractical. A clearunderstanding of whether or not incorporating compost proves to have substantial benefits to soilwater infiltration and retention, as well as grapevine performance, would be of value to the wineindustry. Two methods of organic matter incorporation were compared, namely the furrow ploughand deep tillage or root pruning.In the first experiment, compost mulch was applied on the grapevine row at varying thicknesses in aShiraz/101-14 Mgt vineyard near Stellenbosch. Results showed that the application of compostmulch to a thickness of 16 cm had no effect on soil water content to a depth of 90 cm compared tothe bare soil. While greater fluctuations in soil water content occurred in the 0-30 cm layer, thetreatments did not differ with respect to soil water content over the two seasons. However, waterinfiltration rate increased with mulch thickness, i.e. the highest infiltration rate was observed in thesoils under the thicker mulches. Nevertheless, the thicker mulches, i.e. 8 cm and 16 cm, appearedto intercept rainfall when relatively small events occurred. Under the prevailing conditions, the mulchwas not effective in maintaining a higher soil water content on the grapevine row compared to baresoil. Grapevine water constraints were also not affected by compost mulch, regardless of thethickness. However, vegetative growth and yield responded positively to mulch thickness over thetwo seasons. Since water constraints did not differ in response to mulch thickness, improved wateruptake was not considered to have contributed to the improved growth and yield. Fine rootdevelopment observed in the shallow soil layers under the mulches could have contributed to thegrowth response by allowing for improved nutrient absorption. The mulch had weatheredsubstantially after two years, which was attributed to the maturity of the compost and the quantity offine material.In the second experiment, compost was incorporated using a furrow plough during the root pruningaction, 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 vineyardnear 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 tendedto increase infiltration rate. Higher infiltration rates are expected to reduce water loss by runoff andincrease in the amount of water entering the soil. However, the tillage and compost treatments hadno effect on the soil water content on the grapevine row. It would seem that there was limited lateralflow of water from the work row to the grapevine row. After two years, the furrow plough with compostand 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 thefurrow plough could be attributed to a slightly higher soil water content in that layer where thecompost was concentrated. The penetration resistance in the soil of the control exceeded the 2000kPa threshold for inhibited root growth at a depth of 12 cm. The soil loosening action of the rootpruning with compost is expected to allow for improved root development to a greater depth than thefurrow plough treatment. However, the furrow plough treatment may have encouraged rootdevelopment 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 soilpH increased, probably due to the high amount of calcium in the compost and the dissolution oforganic 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 theshallow 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 ofsodium in the soil increased, the extractable sodium percentage was in fact reduced in the 0-15 cmsoil layer, due to the high amount of calcium. The extractable sodium percentage was also well belowthe threshold where sodicity problems would be expected.Under the prevailing conditions, root pruning did not seem to have a positive effect on grapevinevegetative growth and yield. Rainfall during the study was appreciably lower than the long termmean, particularly in 2015. As a result of dry soil conditions the degree of root regeneration in theloosened soil and the subsequent grapevine responses may have been affected. In contrast, wherecompost was incorporated during the root pruning action, growth and yield increased over twoconsecutive seasons. Likewise, where compost was incorporated in furrows, it also had a positiveeffect on growth and yield. It appeared that root pruning in every row with compost did not providesignificant additional benefits to growth and yield compared to the root pruning in alternate rows withcompost. Apart from the slightly higher pH and lower colour in the wines of the compost treatmentsin the first year, juice and wine quality characteristics were not affected by any of the tillage orcompost treatments. The higher potassium content in the soils measured two years after thecompost was applied appeared to have had no effect on juice and wine quality. Cover crop growthalso responded positively to the addition of compost. It is interesting to note that the enhanced covercrop performance did not appear to compete with the grapevines. Decomposition and mineralisationof the cover crop residue in the vineyard would be expected to further improve organic matter andnutrient accumulation in the soils where cover crop dry matter production was high.

[发布机构] Stellenbosch University