SOIL PREPARATION

FIGURE 7.11: Result of soil loosening between rows with the soil mix implement; subsoil was brought to the surface causing poor water infiltration (Photos: J.E. Hoffman, Stellenbosch University). A field trial executed on soil that was classified as Tukulu and Oakleaf demonstrated that there are soils where the soil mixer may be effective (Hoffman et al ., 2016). This implement was compared to a delve plough and the aim was to loosen the soil down to a depth of 1 000 mm. The results of the trial were compared in 2010 , i.e. six years after execution in 2004. The delve plough and the soil mix implement both gave similar results in terms of bulk density, saturated and unsaturated hydraulic conductivity as well as shear strength, and this result was confirmed by the excellent root distribution on the respective treatment plots. The first abrupt decrease in root penetration occurred at 1.0 m in the rip/soil mix combination and at 1.1 m in the rip/delve plough treatment. The wiggle plough (Figure 7.12) was introduced to grape growers in South Africa in the late 1970s. This plough was equipped with two tines that moved backward and forward when connected to the power take-off of the tractor. This oscillating plough had two tines 50 cm apart and could reach a soil depth of 50-60 cm. The advantage of the wiggle plough over conventional one or two-tine rippers was that it required less power to draw it and consequently a smaller tractor (45 kW) that easily fits between vineyard rows. Furthermore, it gave a better (deeper and wider) loosening action. At the time it seemed to be an ideal implement to alleviate soil compaction in existing vineyards and also for conducting root pruning. The use of the wiggle plough has, however, been discontinued due to its severe shaking effect on both tractor and driver. Since then, a prototype oscillating two-tine ripper has been built and tested in Australia by the University of South Australia for alleviating soil compaction in vineyards (Shahgoli et al ., 2009). This ripper has, however, not been commercialised due to similar vibration problems to those experienced by operators of the wiggle plough (Saunders, 2018).

118 | CHOICE OF IMPLEMENT FOR SOIL PREPARATION