SOIL PREPARATION

CHAPTER 2

have low porosity and permeability (Figure 2.9). Grey colours, an indication of wetness, are consequently found in saprolite, G horizons and non-diagnostic gleyed loam or clay below non-hydromorphic diagnostic B horizons. Disadvantages that are associated with waterlogging include the following: i) Waterlogging limits the size of the root system and, surprisingly, water stress can be experienced during drought periods. ii) Wet soils are seriously compacted by tractor and implement traffic. iii) Tractors and implements get stuck in waterlogged soils and it is consequent- ly not possible to spray vineyards or till the soil on time. iv) Root diseases flourish under wet conditions. v) Due to the slow N-mineralisation under wet conditions, more N-fertiliser must be applied to wet soils than on well-drained soils to get the same plant response. vi) Toxic concentrations of iron, manganese, sulphides, nitrates, ethylene and organic acids are formed. vii) In warm dry climates, soils containing a water table can become saline due to the capillary rise of water and salt to the soil surface.

FIGURE 2.9: A wet Katspruit soil that is unsuitable for sustainable grape production and cannot be drained due to slow permeability. Ridging can be considered to improve the soil (Photo: ARC Infruitec-Nietvoorbij).

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