FERTILISER GUIDELINES FOR THE WINE INDUSTRY

ROLE OF SURFACTANTS

Surfactants are chemicals that lower surface tension, which is the force that prevents surfaces from being wetted. Surfactants act at two levels: • They increase the area of contact and retention time in the “nooks and crannies” of the foliage, and • they modify the external wax barrier, making it more permeable. There are two types of surfactants: ionic and non-ionic. In grapes, treatment with surfactants has been shown to make nutrients more available. Non-ionic surfactants work better than ionic ones because they: • are inert in the presence of salts, • they are compatible with most organic ions, and • they do not form insoluble salts in the presence of hard water. ROLE OF CHELATES The word chelate is derived from the Greek word for “claw”. In fertilisation technology it refers to inorganic nutrients that are enclosed by an organic molecule. Currently, micro-nutrients are divided into the following categories, namely: mineral oxides, mineral salts, and the following chelates: EDTA, DTPA, ED DHA, fulvic acids, amino acids and carbohydrates. TABLE 23: Time duration for the absorbtion of 50% of the elements applied as foliar nutrition.

6

Nitrates, sulphates, oxides

Synthetic chelates

Organic complexes

ELEMENT

Nitrogen (Urea)

1 to 6 hours

1 to 6 hours 7 to 11 days

12 minutes

Phosphate Potassium

15 days 4 days 6 days 5 hours

2 hours

2 days 3 days 1 hour

1 hour

Calcium

2 hours < 1 hour

Magnesium

85