Chapter 18

Fertigation Systems for Vineyards

Fertilizer Application Considerations

A large range of fertilizers, both solid and liquid, are suitable for fertigation depending on the physicochemical properties of the fertilizer solution. For large-scale vineyard operations, solid fertilizer sources are typically a less expensive alternative to the commonly used liquid fertilizers. The solubility of these fertilizers does vary greatly. When switching to a solid fertilizer source, problems can be avoided in the nurse tanks by ensuring that ample water is added to the stock solution.

Fertilizer Compatibility

Most soluble fertilizers suitable for liquid feeding are compatible at their dilute concentration. However, certain chemicals will react at higher concentrations to form insoluble precipitates. These precipitates can tie up the intended nutrients and clog the irrigation equipment. For example, mixing ammonium sulfate [(NH4)2SO4] and potassium chloride (KCl) in a tank reduces the solubility of the mixture due to the potassium sulfate (K2SO4) formation.

Fertilizer Formulations

Fertilizers applied in irrigation water may be purchased dry granular or as liquids. Preparation of nutrient stock solutions from dry fertilizers may require considerable time and effort and can generate sediments and scums as waste products.

Liquid Fertilizers

Liquid fertilizers are available as fertilizer solutions and suspensions, both of which may contain multi-nutrient or single nutrient materials. Solutions are defined as liquids that have all the plant nutrients in a solution while suspensions hold part of the plant nutrients suspended in the liquid by a suspending agent.

Granular Fertilizers

As mentioned, dry granular formulations must be mixed with water to form a stock solution. When mixing granular fertilizers it is better to start with about half the required amount of water in the tank. Then, while continuously stirring/agitating the water, begin adding fertilizer (in small increments) and water until the desired quantity of fertilizer is dissolved in the stock solution.

Fertilizer Solubility

Highly soluble fertilizers are required for fertigation systems in order to minimize potential plugging problems. Dry fertilizer materials differ widely in water solubility, with solubility depending on the physical properties of the fertilizer as well as the irrigation water temperature and pH. Solubility generally increases with temperature, but some fertilizers actually cool the solution such as urea, ammonium nitrate, calcium nitrate, and potassium nitrate when dissolving.

Effect of Temperature on the Solubility of Fertilizers

Generally, the water temperature, under field conditions, is higher than 68 degrees F (20°C). Therefore, it might seem logical to assume that at the time of preparing a liquid fertilizer, that the higher the water temperature, the greater the amount of fertilizer that can be dissolved. However, when making stock solutions that will not be injected soon after preparation, keep in mind that solubilities decrease when the solutions are cool.

Jar Test

Before adding fertilizer to the supply tank, test the compatibility of fertilizers using the “jar test.” Take a clean jar and fill it with water from the irrigation system water supply. Add a small amount of the chemical to be injected so that the concentration is slightly higher than anticipated for injection, than shake well.

Water Quality

For successful fertigation, careful attention must be given to water quality. The quality of water required depends on several factors, but foremost is the type of fertigation. Drip fertigation requires the highest quality water, i.e., free of suspended solids and microorganisms that plug small orifices in emitters. Only liquid solutions should be used for drip fertigation. As the orifice size increases (e.g., on sprinkler systems) suspensions can be tolerated.

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