Technical Yearbook 2023

PHOTO 12. Clods have broken in the subsoil and roots grow around this area. This is a result of overly dry conditions during soil preparation.

PHOTO 11. Soil that has been rolled with a heavy-drag roller to break up clods after soil preparation. This can lead to severe recompaction and crust formation, and is thus an undesirable action. Surface compaction/crust formation Crust formation is a common yet subtle problem in vineyard soils and can occur due to physical and/or chemical causes. Crust formation is more common on bare soils than on soils with a cover crop, and the intensity thereof can vary depending on the parent material of the soil. The primary physical cause of this phenomenon is excessive or incorrect cultivation which destroys the soil structure. It results in densification of soil particles, reduced porosity and the formation of a crust on the surface which restricts movement of water and air to the deeper soil layers. Runoff of irrigation water subsequently occurs on the berm, which in turn leads to impaired water infiltration to the subsoil. Soil chemical factors also have a significant impact on the carbon content (organic material) and concentration of soluble salts (especially sodium and magnesium) in the topsoil. A decrease in carbon content and increase in the sodium and magnesium concentrations cause dispersion of clay particles, and to such an extent that the soil’s surface structure disintegrates, and clay seals the surface with a layer restricting water and air movement. The effective utilisation of rainfall and irrigation water to supplement the ground water, is thus negatively impacted. Furthermore, gas exchange and the balance of aerobic microbial activity (essential for healthy root growth) are also impeded. Cultivation to uplift crust formation will improve water infiltration, but it has to be performed at the right time and with the correct implement. To ensure a long-term benefit, the action has to be supported by chemical additions (gypsum/lime), the establishment of cover crops or laying out a mulch which will eliminate bare areas where crust formation can reoccur. Cover crop practices may vary depending on several factors and the correct practice choice and management actions are crucial. Gypsum (CaSO 4 ) can also be applied to inhibit crust formation (photos 13 and 14). The calcium cations displace sodium and magnesium on the clay particles and help the

soil to maintain its structure so that the clay particles don’t disperse and crusting of the soil is avoided. The amount of gypsum applied must be determined by a chemical soil analysis. Gypsum and laying a mulch or establishing a cover crop are a good combination to fight crust formation.

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14

PHOTOS 13 and 14. A soil crust is a microscopically fine layer of crust which seals the surface of the soil.

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TECHNICAL YEARBOOK 2023