Fertigation Systems for Vineyards
Fertilizers for Fertigation
There are a number of fertilizers specifically developed for fertigation. Some of these fertilizers have characteristics that lend themselves to specific soil conditions, while others are suitable for a wide range of soils. For example, certain soils have an overabundance of sulfur, but require potassium, calcium, and/or magnesium. Whereas acidic soils require potassium, calcium, and magnesium but these soils precludes the use of acidifying fertilizers.
Nitrogen is the most fertigated element in vineyards due to high plant nutritional needs, to its great mobility in soil following chemical and biological transformation to nitrate (NO3¯), and because of the many soluble sources of nitrogen fertilizers available for fertigation.
Monoammonium phosphate, diammonium phosphate, monobasic potassium phosphate, ammonium polyphosphate, urea phosphate, and phosphoric acid represent several water-soluble fertilizers. Nevertheless, they can still have precipitation problems when injected into water with high calcium or magnesium concentrations. These precipitants are very stable and not easily dissolved. Phosphoric acid is sometimes injected into the fertigation system, not only for phosphorus, but also to lower the pH of the water, which can prevent the precipitation problems previously mentioned.
Most potassium fertilizers are water soluble, and injection of potassium through drip irrigation systems has been very successful. The problem most often associated with potassium injection is solid precipitants that form in the supply tank when potassium is mixed with other fertilizers. The potassium sources most often used in drip irrigation systems are potassium chloride (KCI) and potassium nitrate (KNO3). Potassium phosphates should not be injected into drip irrigation systems. The major potassium sources are presented below, along with information on their use in fertigation.
Sulfur (S), when needed, can also be provided as ammonium thiosulfate, ammonium sulfate or flowable S. It can be readily mixed with UAN and several other soluble fertilizer grades and injected. Magnesium sulfate (Epson salts) is often used to supply magnesium and sulfur.
Micronutrients can be applied readily through the drip system. Sulfates of copper, iron, manganese, and zinc dissolve readily in water, and move well through the drip system. However, they are easily oxidized or precipitated in soil, and their utilization is, therefore, not very efficient. Chelated fertilizers have been developed to increase micronutrient utilization efficiency. Chelated forms are more likely to be effective, and can be easily injected. Chelates are generally highly water-soluble and consequently will cause little clogging and precipitation.
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