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.
Fertilizers applied in irrigation water may be purchased dry or as liquids. 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. Suspension fertilizers contain undissolved constituents, whereas the constituents of solution fertilizers are completely dissolved. Dry or suspension fertilizers are mixed with enough irrigation water prior to application to ensure that the fertilizer material dissolves completely and forms a solution (no undissolved constituents).
Preparation of nutrient stock solutions from dry fertilizers may require considerable time and effort and can generate sediments and scums as waste products. Therefore, commercially prepared liquid fertilizer solutions (true solutions, not suspensions) that are completely water soluble are often used.
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.
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.
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 on 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. Consequently, it may not be possible to dissolve as much fertilizer as needed to achieve the desired concentration.
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.
To prevent emitter plugging, fertilizer must be injected upstream from the filter so all undissolved fertilizer material and precipitates will be contained by the filter. It is recommended that the fertigation run should be shorter than the normal irrigation run time, with the fertilizer applied towards the end of the run.
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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