FERTILISER GUIDELINES FOR THE WINE INDUSTRY

FOLIAR NUTRITION Leaves are not really equipped to take up water and nutrients, but rather to pro tect the plant against water loss as well as fungus and other disease attacks. The cuticle on the outer walls is primarily tasked with the uptake of nutrients through the foliage. Elements in the ionic form can penetrate through cracks in the cuticle, as well as through stomates. Foliar nutrition is a useful aid to help the plant with assimilation of nutrients, especially trace elements, when the plant is stressed and roots not functioning effectively. Foliar nutrition should only be used supplementary as it can never replace surface-applicated fertiliser. Foliar nutrition sprays are most commonly used to correct micro-nutrient imbalances. Many micronutrients are readily fixed by most soils and thus become unavailable for the plant during soil fertilisation. A very small amount of microelement foliar nutrition is required to correct the deficiency. Foliar nutrition is a useful way to supplement nutrition in the following condi tions: • Drought and water-logged conditions • Compaction • High leaching conditions

• Injured or infected root systems • Cool periods and slow growth

• Peak requirements for quick response • Imbalances in the soil (high Mg, K, etc.)

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FACTORS IMPEDING FOLIAR ABSORBTION The age of the leaf seems to affect the cuticle thickness. Young leaves have been shown to absorb more. The environment also influences cuticle devel opment, since shade and humidity tend to favour thin cuticles. Finally, hairs on either side of the leaf can also act as barrier. They create hydrophobic surfaces that prevent water from fully contacting the cuticle. The amount of hair (degree of pubescence) of each particular variety should be taken into consideration when deciding on the use of a surfactant.

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