Winetech Technical Yearbook 2022

JANUARY/FEBRUARY

SOIL PREPARATION – THINK BEFORE YOU DO

BY JOHAN DE JAGER

WETNESS Wetness is associated with excessive water or waterlogged conditions in the subsoil, whether permanent or periodical. Soils can also easily become over-irrigated, and oxygen, essential for root respiration, is then displaced through the water, leading to inhibited water and nutrient uptake. Fluctuating water tables During the rainy season, the subhorizon is usually filled with free water. A soft plin thic B horizon (photo 1) has red/yellow/ grey/black mottles resulting from fluctu ating reduction/oxidation cycles. Perched water tables The subsoil regularly becomes waterlogged in the rainy season, which leads to poor root development. Although a typical G horizon (photo 2) has a blue-green or olive tint, indicative of the presence of iron in reductive conditions, grey colours are more typical, and mottles may also be visible. Root penetration is mainly

limited to the topsoil, leading to poor root development and potential root diseases. These problems can be addressed by in stalling drainage (photo 3) to rehabilitate the soil. Installation of correct drainage re quires specialised and expert advice from a specialist in the field. If the problem soils cannot be drained successfully, ridging (photo 4) is the only remaining option. Installation must preferably take place be fore soil preparation. The drainage depth must be sufficient (usually > 1 200 mm) to prevent damage to the drainage pipes during deep soil preparation. If drainage is only performed after soil preparation, compaction of the soil must be avoided as much as possible, and tractor traffic should be limited to the cultivation row and preferably at the drainage trench’s lower side. STRATIFICATION Soils with stratification characteristics fall under the cumulic soil group and are mostly associated with a Dundee soil form

GIVEN THE CURRENT ECONOMIC CLIMATE in the South African wine industry, no one can afford to make mistakes. The cost of establishing new vineyard blocks is cur rently approximately R300 000 per hect are, and soil preparation constitutes about 10 - 15% of this expense. Although the input costs for soil preparation comprise only a small part of the establishment cost, it can have enormous long-term financial consequences if not performed correctly. Before establishing or replanting a vine yard block, a soil investigation should first determine which limiting soil factors may occur in the specific soil to decide on suit able soil preparation actions and imple ments. Accurate data and decision-making are required to ensure that the correct soil preparation actions are performed and that the recommended depth is reached. Similar or general limitations are often observed in the various wine regions. This article will focus on soil limitations, including wetness, stratification and compaction.

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WINETECH TECHNICAL YEARBOOK 2022