SOIL PREPARATION

CHAPTER 9

Further evidence of the harmful effect of tractor wheels is provided in Figure 9.4. Most of the re-compaction occurred within the first four months after the vineyard was planted. Consequently, wheel tractors should not be used on newly-prepared soil for at least one year after planting, i.e. until roots have exploited the entire available soil volume.

Soil Strength (kPa)

0

1000 2000 3000 4000 5000

0

-10

-20

-30

-40

Soil Depth (cm)

-50

Between tractor tracks after 4 months On tractor tracks after 4 months On tractor tracks after 4 years

-60

FIGURE 9.4: Re-compaction by tractor wheels on a Glenrosa soil after soil preparation (redrawn after Van Huyssteen, 1983).

Re-compaction in existing vineyards, especially under the tractor tracks between rows, can sometimes be so severe that it requires deep loosening of the soil. Tractor track compaction can cause a mechanical impedance that forms a barrier to lateral root growth (Schulte-Karring, 1976). This author introduced the wiggle plough to South Africa and demonstrated that this implement could effectively loosen the soil between the vine rows from track to track to a depth of 55 cm. Such an action will allow ramification of the existing roots which are cut and also allow new roots to grow through the cracks caused by the implement (Schulte-Karring, 1976). It should, however, be remembered that deep tillage between vine rows is a form of root pruning, the effect of which has not been well-researched in vineyards (see discussion in Chapter 4).

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