Written by:

Sang Ravindran | Farm Business Consultant | 0436 687 530

Originally ‘created’ for the intensive horticulture industry, the foliar nutrition application is now a common practice and often used in different agricultural industries. The uptake of this technique (see what I did there?!) is popular as the uptake of nutrients through the plant’s foliage can be up to 10 to 20 times more efficient than what plants can take up through the root!

So how exactly does foliar uptake work? There are several ways for foliar substances to enter the cytoplasm of the leaf’s cell. It can either make its way past the cuticle (the waxy layer on the leaf which has 3 layers) or there are often small cracks in the cuticle (stoma and epidermis) that can also serve as an entryway. The important thing to note is that most of the stomata are located on the underside of the leaves which makes foliar spraying more efficient, and these ‘breathing holes’ allow CO2 to enter which then kickstarts photosynthesis to occur. Stomata also act as thermoregulators (allow the plant to transpire) and they actually close at night and at the hottest part of the day. This is another important factor to consider when it comes to the timing of the application, and it became quite critical. Early mornings/dusk are the ideal time for applications
as that’s when the stomata are more likely to be open when temperatures are lower, humidity is higher, and the temperature is <25C.

Figure 1: Leaf anatomy

The main purpose and intent of foliar spraying are to increase the baseline Brix readings over time. A well-designed foliar spray will spike the Brix levels and as the plant gains vitality over time, the spike in Brix is retained longer and over time it can retain a higher sustained Brix level.

Why is brix important? Brix levels play a big role and impact the plant’s ability to be disease and insect-resistant, more nutritionally dense (due to the lower water content), greater resistant to frost damage (Higher dissolved solid levels in plants also lead to lower freezing point, as higher sugars in the sap mean more antifreeze). It also usually means that soils are healthy in terms of biology (microorganisms) and geologically (minerals) as the uptake of calcium, phosphate, magnesium, boron, and sulfur are needed to rise Brix levels. I have done a previous landline article that takes a deep dive into Brix if you wanted to find out more.

Figure 2: Foliar spray application in action on the farm.

A few other reasons why foliar spraying may be of some interest to you.

• Improve crop quality and rapidly correct deficiencies! Through the use of a refractometer, you can measure your Brix levels (I’ve done a whole article on this if you wanted to read about how important and useful it is to have one on the farm) which determines quality, yield and can indicate what important minerals you may be missing in a very short amount of time.
• Provides nutrients in problematic soils where there is limited biology, which inhibits the uptake of soil nutrients to the plant. Examples of this are waterlogged or compacted soil and especially leaching-prone soils.
• Relieve crop stress from late frosts, water logging, increased pest/disease pressures, and drought.
• Increase yield by manipulating the metabolism of plants so that the vegetative phase can be swung into a reproductive phase when fruit or seeds are desired. Can be very valuable in the horticultural industry which could mean you are the first grower to start producing crops which could have advantages.
• To build nutrient-dense produce and high protein levels, especially in the pastures.
• Chlorophyll management – chloroplasts produce glucose which we know is the main food source for the plant. The plant makes glucose via photosynthesis and pumps half of that glucose produced down into the roots in the late afternoon, and 60% of that half is pumped into the surrounding soil to feed the beneficial organisms to create a beneficial relationship.

I’ll finish off with a quick summary of the importance of creating a ‘synergistic stack’ and things that are often included in creating an efficient foliar spray. As always, please do your own research and test the products on a small area of the crop first if you decide to create your own product. Synergistic stacks are a combination of products to help create a stronger response to the baseline plant Brix levels and overall plant health. It starts with addressing plant nutrition (some sort of fertiliser product) by supplying mineral nutrients to the plant, followed by a plant biostimulant such as seaweed, kelp, fish products etc, microbiological biostimulants (humic and fluvic acids, and fungal and bacterial inoculants (compost teas which can be made up of compost/humus/BAM products).

Figure 3: Simple tank set up on our farm experimenting in creating the ‘synergistic stack’.

If you wanted to learn more, the following list is some of the sources where foliar nutrition is discussed in more detailed and where I have collected some information: John Kempf, Jerry Brunetti, Graeme Sait and  research papers “Response of Wheat to a Multiple Species Microbial Inoculant Compared to Fertilizer Application” and “Soil microbial inoculants for sustainable agriculture: Limitations and opportunities”.