Handbook for Irrigation of Wine Grapes in South Africa

Chapter 8

3. Number of fine roots, i.e. thinner than 2 mm diameter, are the most important part of the root system, since they are primarily responsible for nutrient and water absorption. Therefore, the higher the number of fine roots, the better they are for optimal grapevine functioning. The roots must also be distributed uniformly throughout the soil and not be concentrated in clusters or layers. It must be noted that all fine roots are considered to be feeder roots, no matter at what depth they occur in the soil profile. 4. Quality of the fine roots: If roots have a brown colour, it means that they are healthy. Black coloured or slimy roots are unhealthy, or have died back. Figure 8.1

Grapevine

Middle of work row

1

A

B

2

1

3

4 and

and 3

4

C

FIGURE 8.1. Diagram showing the criteria for evaluation of grapevine root systems, where  indicates lateral distribution,  depth distribution,  number of fine roots and  quality of the fine roots.

Figure 8.2 If root systems are not deep enough, it is almost impossible to enhance root depth in existing vineyards. However, where limited roots occur in the middle of the work row (Fig. 8.2A), the following corrective measures can be taken to improve root development. A ripper with a mechanical action that is driven via the power take-off of the tractor, e.g. a wiggle plough, can be used to loosen the soil between wheel tracks (Fig. 8.2B). If compacted soil on the wheel tracks restrict roots distribution into the work row, first loosen the soil between the wheel tracks. This must be followed by ripping on wheel tracks using a two-tine ripper. Loosening the soil in this sequence will minimise soil re-compaction on the wheel tracks. New roots will not only develop into the loosened soil, but numerous roots may form where thicker roots were cut during tillage. This stimulation of root growth is referred to as the “root pruning” effect (Fig. 8.3). Corrective measures should be carried out during the post-harvest period when wheel traffic is low. If waterlogging causes dead or unhealthy roots due to lateral subsurface water flow into the vineyard, cut-off drains must be installed.

IRRIGATION OF WINE GRAPES 237