In discussions about foliar feeding, the question often arises whether this cultivation measure makes sense. After all, the absorption of minerals is the work of the roots. That’s right, but the leaves also make a considerable contribution. This is confirmed by scientific research over and over again. The leaves of most plant species are very well equipped for the absorption of water, amino acids, other organic compounds and even whole minerals. In this article I will explain how this works.
In the course of their evolution, plants have developed multiple systems to survive and reproduce successfully under poor conditions. Food intake through the leaves is one of these indispensable backup systems.
A good example for the natural process of foliar feeding can be found in dark rainforests. In these forests with high rising trees, the understory of herbs and shrubs don’t get a lot of direct sunlight if any. As a result, photosynthesis is low and produces only a limited amount of simple sugars for growth, root growth and root exudates.
The roots receive part of these sugars. On their turn they exude most of these sugars into the surrounding soil as food for microorganisms. (Rhizosphere) In turn the microbes release the required minerals and organic particles for absorption by mycorrhiza and root hairs. (indeed, not only ions are transferred)
At low photosynthesis level, fewer but maybe even more important, simple sugars are released to the soil. This results in limited maintenance of the soil organisms followed by limited absorption of minerals.
Pathogens are easily attracted by “simple” sugars. The more complex the sugars from photosynthesis, the higher the disease resistance. Plants in dark forests would never be able to survive under low photosynthesis conditions without alternative ways to produce high quality sugars. Most plants developed a secondary absorbing system. They succeed by actively absorbing amino acids, minerals and even organic humus fractions through their leaves. This natural foliar feeding comes from the canopy layer of the forest, where fine (organic) dust particles, dead insects, bird droppings, algae and mosses gather. The nutrients that are released drop on the understory plants. Because most cultural crops originate from forests, they can usually process foliar feeding very well.
For decades, researchers and companies are looking for ways to grow plants to their genetic optimum. Most cultured plants that grow on conventional fertilizing systems and thus necessarily supported by fungicides and insecticides reach up to 60-75 % of their genetic growth potential. One of the limiting growth factors in organic farming is that fertilization needs of plants are often still based on the ideas that came with chemical fertilizers. Justus von Liebig’s “Law of the minimum” is only one example for this matter. Regular foliar feeding might be one way to achieve a healthier and resilient crop and even increased yield. Both in organic and conventional farming.
There are basically three ways in which minerals and amino acids can be absorbed through the leaf: through the leaf hairs (triads), through the wax layer on the leaf (cuticles) and by absorption and release via cells (endocytosis).
Most plant species have a few hundred times more stomata in the underside of leaves than on the upper surface. That’s a signal they’re not designed for water uptake. The stomata are well equipped for breathing and evaporation, but as water absorbing organs they are just as suitable for the plant as drinking through the lungs for human beings.
Triads are single-celled outgrowths of the epidermis. Positively charged minerals and amino acids are usually well absorbed through these bulges. The negative charged plants can also pull in positive charged foliar fertilizers in very small amount through their wax layer. Organic foliar fertilizers normally don’t pass through the cuticula (Wax layer) However, Many chemicals, especially fungicides, pass through the wax layer by dissolving this protective sheath. That is one of the reasons that chemical sprays need to be repeated almost weekly. Once the wax layer on the leaves is (partly) dissolved or shows holes, the leaves are practically defenseless and prone to attack of pathogens.
With endocytosis, minerals lying on the leaf are enclosed by epidermal cells and transported to so-called storage cells (sink cells), which absorb and store the minerals for later use. The figure below shows the first part of this process. The principle actually works the same as medicine patches on the human skin, which slowly release medication to the body through the skin.
Absorption of nutrients through leaf via endocytosis
For many decades, the 17 well-known macro and micro elements that plants need according to current fertilization theory have been used throughout the world. Supplemented with oxygen, water and CO2, counts up to 21 elements. Some old and more recent research supports the view that , plants absorb much more from the soil than only the minerals in Ion form as assumed until today by most researchers and agronomists. Lots of research also claims that humans and animals also need more elements than the common list to function in a healthy way. Supported with an increasing amount of literature we now know that humans and animals would need at least 30 and as much as 60 elements. To function healthy.
This includes quite a few rare earth elements. These are elements that occur in almost every soil type in very small quantities. Research on the use of very small amounts of elements like Lanthanum and Cerium shows quality and harvest improvement in several arable crops. The minerals required for growth should be placed in the group of essential minerals.
The rare earth elements that are not considered as useful (yet) but have shown to have an effect on health, flowering, fruiting, germination and so on should be categorized in a group of beneficial elements.
Well considered, it is now known that plants need more than 17 basic elements to express healthy growth. It is also plausible that, after many years of harvesting, rare earth elements are no longer present or insufficiently present in agricultural soils. This soil impoverishment can also help explain the declining nutritional value of agricultural and horticultural crops over the past 40 years.
Through this progressive insight, both researchers and farmers have begun to enrich old farmland with stone flour. (also called: rock dust or rock flour) This fresh ground product contains trace elements that are not found on any classic fertilizer analysis. In Netherlands, Germany, Switzerland USA and Austria in particular, there has already been a lot of positive experience with rock dust.
Much research is still needed to get all the facts out and to rule out uncertainties. Growers can wait for that, but they can also anticipate. This can be done by spreading rock dust or, even better, a combination of rock dust and beneficial soil bacteria. (TerraPulse from PHC.)
A faster way to experience that plants appreciate a wider range of minerals is foliar feeding. Good leaf fertilizers do not contain high amounts of nitrogen. Instead, they contain many types of amino acids with an18-20% presence in the product. They should have a number and a variety of elements that are only found in organic fertilizers. Plants very quickly show whether or not foliar feeding is functional. For growers, it is a quick and practical way to steer the plant growth as needed and to better guide the fruiting and ripening. Foliar feeding is a complete natural phenomenon, which has been around since plants grow on earth.
Plants under heath or drought stress close their stomata to reduce evaporation. This also reduces photosynthesis. At the same time the supply of water and nutrients is slowed or even stopped. The result is a severe reduction of growth potential. Providing extra water under these conditions will bring some relief when the temperature drops. Like stated before, a reduced photosynthesis produces fewer complex sugars, making the plant vulnerable to disease and insect attacks. The fast turnaround from this situation is to make sure that the plants increase their photosynthesis to enable them to produce complex sugars quickly.
This improved growing condition can be created by spraying 4-5 liters/hectare on 200- 400-liter of water with Organic plant based fertilizers (OPF from PHC) that contain high organic and amino acid content as foliar feed. Under no circumstances this will cause leaf burn. However, it is to be advised to give foliar feed early in the morning to enable the plants to make full use of the extra nutrients.
The plants will respond very quickly and thankfully to this treatment. They will show this by their reaction. An important side effect of foliar feeding is the production of high quality sugar complex that will feed the roots and the rhizosphere. This results in better maintenance of the mycorrhizal colonization of the roots and thus a higher water absorption capacity.
Foliar feeding of plants is much more important than suggested by many. In the near future, farmers will see the potential of foliar feeding with all natural plant based fertilizers.