Knowledge article

The (non)sense of foliar fertilisers

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Applying foliar fertiliser may appear to be a relatively new phenomenon, but did you know that we discovered the ability of plants to absorb water and nutrients through their leaves more than three centuries ago? And that foliar fertilisers have been applied in agriculture since the early 19th century?

Why use foliar fertilisers?

There are various reasons to treat agricultural and horticultural crops with foliar fertilisers, with the main ones being:

1. To quickly correct a nutrient deficiency during the cultivation cycle; foliar fertilisers usually have an effect within a week so that any yield and quality losses are minimised.
2. To satisfy the nutrient requirements if the possibility to uptake nutrients via the soil is limited; trace elements such as manganese are difficult to absorb with a soil pH higher than 6.2 (Soil & Fertilisation manual). An application of a foliar fertiliser can then provide the required manganese.
3. To protect and feed the crop in a single pass; in some cases, fertilisers can be combined with a crop protection treatment. Check beforehand if the desired tank mix can physically be mixed (miscibility).
4. Feeding the crop optimally within the restrictions of the legally permitted standards for maximum dose rates of nitrogen, phosphate and animal manure it is not always possible to fully satisfy the nutrient requirements of the crop. By supplementing the basic fertiliser dressing with an efficient foliar fertiliser, achieving a high output is still possible.

Important conditions

The effectiveness of foliar fertilisers varies widely relative to the species of plant and depends on a number of factors:

• Plant characteristics: each plant species has its own characteristics. Plants with water-repellent leaves (various brassicas) or a thick waxy layer absorb water and nutrients less easily (Fernandez, 2013). The growth stage of the plant is also important. Most plants absorb nutrients best during the exponential growth phase (Alexander, 1986).
• Weather conditions: Plants uptake fertiliser optimally if the liquid sprayed on the foliage does not dry out too quickly. The ideal time for treatment is in conditions with high relative humidity, a mild temperature, not too much sun and a low wind speed (WUR, 1994). Preferably spray the foliar fertiliser in the early morning or late evening.
• Quality of the foliar fertiliser: complexed foliar fertilisers have a greater stability in the solution and are therefore more easily absorbed than a fertiliser containing only the active nutrient (Alexander, 2016). So, in addition to the costs, also pay attention to how the product has been formulated.
• Application method: foliar fertilisers are often applied with an ordinary field sprayer. Spray nozzles that create a fine droplet ensure the best leaf coverage, but this type of nozzle does not always comply with drift reduction guidelines. Pay attention to this aspect when choosing the nozzle.

Risks

Spraying foliar fertilisers is not always without risks. Leaf burn is one of the most common consequences of incorrect spraying practice. Leaf burn is usually the result of a too high dose rate, or the foliar fertiliser drying too quickly on the leaves. The miscibility can also be an issue, not all foliar fertilisers can be combined with other substances. Check the instructions for use for information on the miscibility or consult your supplier.

Complexed foliar fertilisers

The Soiltech portfolio offers a wide range of liquid foliar fertilisers. The foliar fertilisers are organically complexed. This means that the active nutrient (e.g. manganese or copper) is bound to an organic molecule. An organically complexed fertiliser offers several advantages over a non- or chemically complexed fertiliser:

• The fertiliser is less aggressive and has a lower risk of burning the crop.
• The active nutrient is easily absorbable via the leaf.
• The fertiliser has greater stability and can be more easily combined with other substances in a tank mix.

Research

The R&D department at Soiltech has a professional greenhouse which is used to study the safety and efficiency of the foliar fertilisers An automated spraying installation enables highly accurate dose rates. Soiltech tests the safety of foliar fertilisers in the greenhouse on crops including radishes and beans, because these crops are sensitive to burning and scorching. Following extensive screening in the greenhouse, field trials are conducted on crops in practical situations.

Would you like more information about the combinability of Soiltech's (foliar) fertilisers, biostimulants and excipients? Click here!

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