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Foliar fertilization – does it make sense?

The uptake of nutrients from the soil is influenced by a number of factors. Some of the most common factors that can limit uptake or availability to plants are soil temperature, pH, fixation of nutrients, root problems or diseases, or even just physical deficiencies of nutrients.

The use of foliar products as a supplement in fertilizer programmes is widely known, and is usually implemented with great success. In addition to a supplement, foliar sprays are also used to manipulate certain physiological processes in the plant or crop. The efficacy of foliar application depends on a number of factors, including:

Crop – the crop itself, morphology of the leaf, growth stage, leaf arrangement, etc. Environment – temperature, wind, relative humidity, etc. Chemical – element and the form in which it appears, concentration, ionic charge, pH, etc. Physical – droplet size, particle size, wetters, etc.

Micronutrients are often applied as foliars feeds. The reason for this is that plants need relatively small doses of these elements and also because they are easily fixed in the soil. The benefit of foliar sprays is that they can be applied at the right growth stage and that plants usually react very quickly. 

The purpose of a fertilizer programme should always be to ensure that all the nutritional needs of the crop will be met in order to ensure optimal production. This is also the case with foliars. The spraying of products on leaves when it cannot be transported or translocated to where the plant needs it, should be avoided. It also does not make sense to apply foliar products if the plant doesn't need the nutrients, unless the purpose of the application is to manipulate a process in the plant. An example of this is to apply hormones to stimulate root development.

Omnia developed the PLUS range specifically to address micronutrient deficiencies by applying it with the fertilizer in the band. The formulation is adjusted regularly by the agronomic team and is based on soil, OmniSap® and leaf data from the different regions. Despite the yield increases achieved through these products, deficiencies still occur, which will have to be addressed. This can be seen in the example in Figure 1.

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Figure 1: The OmniSap® analysis on the left was done on maize not fertilized with the PLUS product, whereas the sample on the right was fertilized with the PLUS product.

Omnia also markets a wide range of speciality products formulated with diferent combinations and ratios of nutrients and hormones which can be applied to crops as foliar sprays.

During a recent trial on wheat in the Northern Cape, a number of foliar products were compared at a young growth stage. Figure 2 shows the effect of the different products on the yield of wheat.

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Figure 2: Yield reaction of wheat to foliar fertilizers

From this, it is clear that a number of treatments lead to yield differences. Regarding the quality of the wheat (protein content), there were smaller differences compared to the control (Figure 3).

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Figure 3: Influence of treatments on the protein content of wheat

Some of the treatments had little or no influence on yield, but did result in an increase in protein content. This confirms the fact that plant nutrition is a complex subject and that it is best to rather consult an agronomist before foliars are applied.

When specific nutrients are considered, it is important to take the target area where the nutrient is needed into consideration, as this will have an effect on the form of the nutrient, as well as the method of application. Table 1 shows the mobility of every nutrient in the phloem of plants.

Relatively mobileAverage mobilityLow mobility
Potassium Sodium Calcium
Nitrogen Iron Silicon
Sulphur Zinc Manganese
Magnesium Copper Boron (crop dependent)
Phosphorus Molybdenum  
Boron (crop dependent)    

Table 1: Mobility of nutrients in the phloem of plants (Epsteim and Bloom, 2005)

The form of the element is also important. There are different opinions regarding the use of chelates, oxides, sulphates, etc. and this sometimes causes confusion. The following guidelines should be kept in mind to ensure that the correct products are applied:

  • Iron – if the pH in the phloem varies between 7.8 and 8, the iron will be insoluble and wil therefore have to be applied in a complexed form.
  • Zinc – is more mobile than iron and translocation from necrotic leaves can occur.  During grain fill, considerable amounts of zinc are also translocated from other plant parts. It is a fact that only about 5 – 20% of the zinc applied to leaves is translocated. Except for the poor penetration of zinc, leaf tissue also fixes a lot of zinc entering the leaf. Sulphates and chelates show good reactions, and there have even been cases where good results were obtained using zinc oxide.
  • Manganese – even though manganese is mobile in the phloem, only small amounts can be translocated. Manganese sulphate and manganese EDTA are commonly used.
  • Boron – even though boron is taken up quite well through the cuticle and all membranes, it is not very mobile in the phloem of most plant species. Therefore, the best reaction from boron fertilization is when it is applied through the planter mix.
  • Copper – is very immobile and can also be easily fixed in the soil. Copper sulphate and copper EDTA are commonly used as foliars where deficiency occurs.
  • Molybdenum – is relatively immobile in plants, and since it is needed in such low quantities, a foliar spray is usually sufficient. Products such as sodium molybdate or MOLIBOR™ are generally used.

Products that are used to manipulate crops include ORGANOCELL™, KELP-P-MAX®, X-PLODE®, SUPRASET and OMNIBOOST®. The reasoning behind this is explained in Table 2.

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Table 2: Reasoning behind the use of certain products to manipulate crops

Foliar fertilization has the potential to be a useful management tool on the farm, if it is used economically, efficiently and sustainably. Omnia not only has the expertise, but also the resources, to ensure that every drop that lands on the leaf, will end up as profit in the farmer's pocket.

Sources / Bronne:

  • Epstein, E. en Bloom, A.J., 2005.  Mineral nutrition of plants:  Principles and perspectives, 380.
  • Fernandez, V., Sotiropoulos, T., Brown, P., 2013.  Foliar fertilization:  Scientific principles and field practices.  International Fertilizer Industry Association.  Paris, France.
  • Papadakis, I.E., Protopapadakis, E., Therios, I.N., Tsirakoglou, V., 2005.  Foliar treatment of Mn deficient 'Washington navel' orange trees with two Mn sources.  Scientia Horticulturae 106 :
    70 – 75.

By André Labuschagne and Kevin Fourie (Agronomists)