putting the strainers into the ground far enough, which leads to them being pulled out; or (iii) soil not being strong enough to bear the load, which leads to strainers tilting or moving through the soil (see Fig. 6.26). A thorough analysis of predicted trellis loading and soil strength, before determining the type of end assembly to use, will prevent costly repairs and lost crop in the future.
and microorganism populations, and herbicide use is expensive and can have adverse impacts on the environment (Doran, 1980; Pankhurst et al., 1995;
Roper and Gupta, 1995).
Therefore, some form of planting in the vineyard system can have beneficial effects, such as reducing erosion, dust and undesirable weed development and increasing water infiltration rates, soil organic matter, quality of soil structure, populations of beneficial organisms and vineyard accessibility (for, e.g. workers, tractors and harvesters), especially in wet conditions (Hartwig and Ammon, 2002). Cover crops can also be useful as a tool to manage soil water availability and alter grapevine shoot growth. Disadvantages of cover crops include the need to prepare soil, buy seed, and plant and establish the cover crop. In dry areas, its use of soil moisture can be a drawback, as well as introducing competition for nutrients. A vegetative cover on the soil also lessens heat accumulation during the day and release during the night, which can increase Fig. 6.27. Cultivated vineyard rows, which leads to less competition for water and more nutrients for the vines.
the risk of spring frost damage (Dethier and Shaulis, 1964). Vine root development is altered and some plants can harbour pests such as rodents, diseases, insects and nematodes.
Careful selection of an appropriate cover crop is then warranted; there are many options available. Annual plants are usually shallower rooting and therefore less intrusive on the vines and, if left to seed, do not have to be re-sown.
Perennials have better staying power, but may be more expensive to establish.
A popular option for cover crops are grasses, such as brome, rye, blue and fescue or even a grain crop (see Fig. 6.28). The ability of a cover crop to die back in the summer is usually an advantage as, when conditions are at their driest, it is not competing with the vines for water and nutrients. Cover crops must also be able to survive in between the vine rows, where there is usually no supplemental water. In areas of low nitrogen, legumes may be used as a cover crop to help manage soil nitrogen availability. More recently, flowering plants have been used in vineyards as they attract beneficial insects, resulting in fewer pests (Landis et al., 2000; Nicholls et al., 2000).
In areas with excess available water in the soil, deep-rooted plants, such as chicory, can be planted to help draw water away from the vines (Caspari et al., 1997).
In some cases, a volunteer crop is allowed to become established as a cover crop, which has the benefit of being low cost and will be made up of those plants that are hardy enough to survive in between the rows. However, this volunteer crop may have undesirable characteristics, such as adding nitrogen to the soil, not dying out during the summer months or not achieving sufficient ground coverage to allow foot and vehicle traffic during the wet season.
Fig. 6.28. Oats sowed in alternate rows of a mature vineyard. These are grown to be incorporated later into the soil. In a young vineyard they can be grown to provide shelter from wind damage.
Additional costs are associated with cover crops, such as the need to mow (particularly in the spring in frost-prone areas, as a short grass cover crop has minimal impact on frost incidence) and to keep the cover crop from encroaching on the vines or growing at the wrong time (usually resulting in the need to use herbicides).
During the vine establishment phase it is not a good idea to keep cover crops in the vineyard, unless water and nutrients are not limiting. They should also not be used in areas of severe frost risk or where soil water is at a premium. However, once the vines are established, cover crops can be planted if appropriate (see Fig. 6.29).
Non-living cover crops also exist in the form of mulches, which can be organic or inorganic, and can result in improved weed control, water conservation, soil structure, water infiltration rates and root branching. However, they can also increase vine vegetative vigour, shelter rodents and increase costs (Penfold, 2004).
The use of mulches is often worthwhile during the establishment phase of vineyard development, as it can aid vine growth (see Table 6.2, Fig. 6.30) or in areas of low water availability.
Mulches are taking on other roles as well, in altering the light environment of the vines and fruit. Spreading of mussel shells under the vine rows (see Plate 31) was found to improve ‘Pinot noir’ wine quality, with minimal impact on other performance factors (Creasy et al., 2006). These preliminary results are very promising, and have the bonus of providing an end use for a waste product.
Fig. 6.29. Recently seeded grass in a 2-year-old vineyard.