Foliar fertilization – Is it worth it?

Foliar feeding is not new, farmers use this method since the early 50’s on large scale to alleviate iron, copper, zinc and manganese deficiencies¹. The question is, is it worth applying for small scale farmers. There are pro’s and con’s in foliar feeding which will be discussed in this article. One thing growers must know, foliar feeding is not a magical application that will double your yields. There are very specific conditions when it is economically advantageous to apply foliar nutrition.

It is important to now that foliar fertilizers are very expensive, especially considering the amount you pay versus the yield increase you get to pay for the fertilizer. It is my opinion, and not the opinion of the fertilizer companies selling the fertilizer, that the yield increase will not pay for the cost of the foliar fertilizer under normal conditions. So right from the start I have exposed myself to my own bias, and with good reason (I think). There are very specific conditions that foliar feeding is crucial and the farmer will reap high rewards, but in 99% of the cases, fertilizer companies reap the highest rewards.

What a negative introduction to an article. I hope the controversy will entice you to read on.

Plants get all their nutrients from the soil, but there are some instances where a soil might be deficient in certain elements, or nutrients, which can easily be absorbed through the leaves.

Can leaves absorb fertilizers or nutrients

Plants can absorb the most essential elements through their leaves. That is why pollution can affect plant growth and humans after they ate the plants. Interestingly water and soluble salts are absorbed through the waxy outer layer of the leaf surface, the cuticle. Just because the cuticle is waxy, does not mean ions can pas it². Absorption takes place in three stages, (1) passive diffusion through the cuticle (2) absorption on the plasma membrane and (3) incorporation into the cytoplasm through a diffusion gradient.

Other places of nutrient penetration are the stomata, epidermis cells and leaf hairs. The fastest absorpsion is through the stomata but the most nutrients is absorbed through the epidermis³.

When can foliar feeding help the plant the most

Nutrient deficiencies during critical growth stages can harm a crop’s yield and quality. Foliar nutrition is an effective way to quickly reduce the harmful effect of these deficiencies. While soil-applied nutrients depend on various soil factors for availability, foliar nutrients are absorbed directly by leaf cells and quickly reach the cytoplasm. Factors like nutrient fixation in soil, leaching in sandy soils, extreme soil temperatures, and lack of moisture can reduce the effectiveness of soil applied fertilizers. During later growth stages, early developing fruits demand more nutrients, leaving roots with less energy for nutrient absorption. This can slow crop growth and lower yields. Applying foliar nutrition at these stages can help support the crop.

Below is a list of the most common liquid fertilizers used for foliar feeding.

• Nitrogen Urea (46% N), Di ammonium phosphate (18%N), calcium ammonium nitrate (26%N), ammonium nitrate (35%N) , ammonium
  sulfate (21%N), ammonium chloride (26%N).
• Phosphorus Di ammonium phosphate (46%P₂ O₅), single super phosphate (18-22% P₂ O ₅ )
• Potassium Muriate of potash (58%K₂ O), potassium nitrate (44% K₂ O),
• Calcium Calcium nitrate (19% Ca), mono calcium phosphate, calcium chloride, calcium ammonium nitrate.
• Magnesium Magnesium sulphate hydrate (epsomite) (9.6% Mg), magnesium sulphate
• Iron Ferrous sulphate (20% Fe), ferrous ammonium sulphate (20% Fe), FeEDTA (9-12% Fe)
• Manganese Manganese sulphate (26-28% Mn), manganese oxide (41-68% Mn), manganese chelate (12% Mn)
• Copper Copper sulphate (25% Cu), cupric oxide (75% Cu)
  cuprous oxide (89% Cu), copper chelate (13% Cu)
• Zinc Zinc sulphate (34. 46% Zn), Zinc oxide (77- 80% Zn)
• Boron Borax (11% B ), sodium pentaborate (18% B), solubor (20% B), boric acid (17% B)

Credit featured image: Photo by Aleksander Dumała:

1. H. J. MederskiGarth W. Volk. 1 January 1956. Ohio Agricultural Experiment Station
2. Franke W. Mechanisms of foliar penetration of solutions.Annu. Rev. Plant Physiol 1967;18:281-300.
3. Shabnam K, Kuruwanshi VB. Foliar nutrition of plants. Rashtriya Krishi 2015;10(1):54-55