SOIL PREPARATION

be made for the safe discharge of water that accumulates and runs off the compacted contour roads. Several advantages result from using the terracing system shown in Figure 5.11 together with the stake vines. Less soil is wasted by the terraces themselves and consequently more vines can be planted per hectare. Naturally, the planting distance of 1.0 x 1.2 m also contributed to increase the number of vines. Secondly, vine rows follow the contour of the land which would not have been possible if a trellising system using wires for training of cordons were used. In such a case, straight rows and a different system of terraces would have been needed. Furthermore, the soil surface and therefore the topsoil have been left undisturbed across the entire vineyard. In contrast, grapevines planted on the same farm on old terraces which were constructed by moving topsoil laterally into lower parts, as well as vertically to create the terrace slopes, yielded uneven grapevine performance. Poor growth occurs in areas where the topsoil is partly or totally removed.

SUMMARY TERRACING

• Terracing of sloping land be- comes necessary when inclines become more than approximately 20 %. It is an expensive exercise that should be reserved for ta- ble grapes and high quality wine grapes. Terraces made in the ‘con- ventional’ way should be wide enough to accommodate at least two vine rows. A minimum plant- ing distance of 0.5 m from the shoulder of terraces is recom- mended to prevent drying out of the grapevine root system and to reduce reflection of sunlight on northern and western slopes.

• The width of a terrace is deter- mined by soil depth and the slope of the land. At a 20 % slope and a soil depth of more than one me- ter, terraces can be approximately 6 meters wide. For a similar depth, 4 m terraces can be constructed on 30-40 % slopes, but terrace width should decrease to 3 m on even steeper slopes. • Construction of terraces can be done by using the blade of a crawler tractor or by an excavator. Firstly, the position of the terraces must be pegged out, and ame- liorants e.g. lime and phosphate,

74 | SPECIAL SOIL PREPARATION STRUCTURES