Foliar Fertiliser Developed for Agriculture

Foliar nutrition is a highly effective method for supplying nutrients through the leaves, rather than the roots. Spraying water soluble fertilisers directly onto plant leaves can quickly resolve nutrient deficiencies and replenish crops.

First discovered in the 1870s, foliar nutrition has evolved over recent decades and is now recognised as an efficient, and highly effective method, to supply plant nutrition.

To be successful, foliar nutrition relies not only on a supply of nutrients, but also on the correct interaction between those nutrients and the environment, and physiology of the plants.

Nutrient Source Matters

There are three sources of nutrients for foliar nutrition: inorganic, organic complex, and synthetic chelate. Each of these distinct nutrient sources has distinguishable characteristics, including solubility, molecular size, electrical charge, and deliquescence point. It is the combination of these characteristics which affects the nutrient’s absorption, translocation, and ultimately the efficiency of foliar nutrition.

Solubility and Absorption

For foliar absorption of nutrients to be successful, they must be dissolved, not just suspended in a liquid. Research comparing soluble ZnSO₄ with a zinc oxide in a nanoparticulate, low solubility form, has shown that even if the zinc oxide is at the nanometer scale (smaller than 100 nm), it is still absorbed at a lower level than the sources of higher solubility.

Foliar absorption of zinc from soluble sources can be up to 92 times greater than zinc in nanoparticulate oxide form.

Molecular Size affects Absorption

The different sizes of nutrition molecules influence the speed of absorption through the plant surface or cuticle. The cuticles’ pores can absorb particles up to 2.4 nm, while particles up to 43 nm can pass through the stomata. Research into fertiliser particle size found many have particles with an average size of more than 100 nm, indicating that foliar absorption of these nutrients is unlikely.

How Nutrient’s Electrical Charge Impacts Nutrient Absorption and Translocation

Plants’ leaf cuticles are negatively charged. This means that uncharged or positively charged nutrients will cross the cuticle and have a greater capacity to move within the leaf tissue. Chelated nutrients, with a neutralised electrical charge, have a greater chance of being absorbed and translocated to other plant organs, improving their efficiency.

The Point of Deliquescence

The definition of the point of deliquescence is the level of relative humidity at which a salt becomes a solute. When the air is more humid than this level, the salt compound dissolves and becomes available for absorption by the leaf. This level differs between the different nutrient sources, but it can also be manipulated with additives. For example, it is essential to use surfactants with chelated nutrients, as these drastically reduce the point of deliquescence, meaning that they will be easier to absorb even at relatively low humidity.

Cuticle penetration of different sources of Manganese and Zinc with and without surfactants.

Safety and Compatibility of Foliar Nutrients

The variation between different foliar nutrients does not just affect the ability for absorption and transport within the plants. Another significant consideration is compatibility with other products. For example, mixing nutrients with pesticides in the sprayer tank reduces farm operating costs by delivering both the foliar nutrients and pesticide in a single application. But in some cases, nutrients will reduce the efficiency of pesticide products, reducing efficiency from 70% down to 25%. In other cases, the products may destabilise, causing lumps to form in the solution that can clog the sprayer’s filtration system, compromising flow through the nozzles, reducing the efficiency of foliar nutrition while also shortening the useful life of the nozzles.