Foliar fertilization is the process of applying mineral nutrients, amino acids and other organic substances to the plant leaf, which, through total absorption (passive and active absorption), uses these elements throughout the plant, and is not limited to local leaf therapy. Foliar fertilization is not limited to the application of nutrient solutions only to the foliage of plants; the treatment can extend to new and adult branches, cuttings and trunks through spraying or brushing, which is called stem fertilization (MOCELLIN, 2004).

Foliar fertilizers can supply the lack of one or more micro and macronutrients (especially micronutrients) correcting deficiencies, strengthening weak or damaged crops, increasing the speed and quality of plant growth (MOCELLIN, 2004).

Some characteristics of foliar fertilization are listed below:

Figure 1- Foliar fertilization. Source: ILSA

Another commonly used application is the addition of nitrogen fertilizer to the herbicide application solution, aiming to provide the nutrient to the crop and improve the characteristics of the application solution (CARVALHO, 2009).

Absorption is the entry of an ion or molecule into the internal part of the plant. This process is facilitated when the plant has its stomata open, establishing a transpiration current that “drags” the nutrients sprayed on the surface of the leaf to its interior. Plants have a vast network of conductors, which consist of xylem and phloem. These conductive tissues begin in the roots and move up the stem to the branches and leaves. The suction that exists in the water-conducting cells begins in the process of water evaporation from the leaves. The loss of water from the leaf is comparable to the suction made by a straw. If the vacuum or suction is strong enough, the water will rise up the straw. (MOCELLIN, 2004).

Nutrient absorption by leaves is more effective when the nutrient solution is applied as a thin film, which is obtained through surfactant substances that reduce surface tension (TAIZ; ZEIGER, 2017). According to these authors, the movement of nutrients into the plant involves diffusion through the cuticle, absorption by leaf cells and absorption through the stomatal cleft (REIS, 2021).

For the leaf penetration of solutes (Figure 2), a series of processes must occur, such as adhesion to the leaf surface, which must be maintained for a sufficient time for the solute to penetrate the leaf and, from there, for diffusion to occur through the cuticle (REIS, 2021). Subsequently, there must be desorption from the cuticle to the conducting vessels (phloem) so that the nutrients are transported throughout the plant (KIRKWOOD, 1999). Faquin (2005) mentions that after crossing the cuticle, the solutions penetrate the apoplast and, subsequently, cross the plasma membrane, the second barrier, to then reach the symplast and be used or transported to other cells or organs.

Figure 2 – Stages of foliar fertilization. Source: ILSA.

Furthermore, for foliar fertilization to be successful, damage to the leaves must be avoided. An example would be the time of application, where spraying is applied on a hot day, excessive evaporation may occur and salts may accumulate on the leaf surface, causing burning or drying (TAIZ; ZEIGER, 2017). The main difficulty in applying macronutrients via foliar application is the high quantity required of these elements and the possibility of negative influence on the leaves, causing tissue dehydration (plasmolysis), commonly known as burning (CERETA; SILVA; PAVINATO, 2007).

According to Mocellim (2004), among the factors inherent to plants that can influence foliar absorption are structural characteristics (such as number of stomata); chemical composition (thickness of waxes and cutins) and age of leaves (facilitated in younger leaves). Regarding external factors, there is light, as it influences ionic absorption and stomatal opening; ambient temperature, as high temperatures promote the evaporation of water from the solution and can cause losses or burns in the leaves; atmospheric humidity, which keeps the cuticle hydrated and promotes better coverage surface on the leaf; application methods and occurrence of strong winds, which can cause drift and losses of the applied foliar fertilizer (REIS, 2021).

Thus, foliar application is a procedure used to satisfy the nutrient needs of plants, increase yields and improve production quality, since it is also possible to use modern organic substances that stimulate plant metabolism, help to overcome abiotic stresses and improve the efficiency of fertilizers used in the production system.

These same authors report that among the frequently mentioned advantages of foliar fertilization, the following stand out:

• In situations where suspected nutritional deficiencies are easily diagnosed, the response to the applied nutrient is almost immediate and, consequently, deficiencies can be corrected during the growth cycle.
• The technique has demonstrated positive efficiency when absorption conditions by the root system are adverse, such as: drought conditions, waterlogged soil or extreme soil temperatures.
• In foliar fertilization, it is easier to obtain a uniform distribution of nutrients compared to the application of granulated products or physical mixtures, via the soil.
• Foliar application is more efficient in the later stages of growth, when there is preferential assimilation for fruit production compared to root application, which is limited in time and form.
• Considering the lower absorption capacity of leaves in relation to roots, the doses applied in foliar fertilization are much lower than those used in soil applications.

Nachtigall and Nava (2010) highlight the disadvantages of foliar fertilization:

• In situations where excessive concentrations or poorly formulated products are used, leaf or shoot burns may occur.
• Applications must be carried out in conjunction with other spraying to avoid incurring higher costs.
• Foliar fertilization has a low residual effect, especially for non-mobile micronutrients, such as boron, which leads to the need for more than one application. These frequent applications in perennial crops can lead to an accumulation of the nutrient in the soil, which should be considered when applying annually via the soil.

In a study carried out by Oliveira (2021), it was shown that foliar fertilization with molybdenum was able to improve the physiology and productivity of soybean and corn crops. This was possible due to the improvement in the activity of the enzyme Nitrate Reductase, which in turn promoted an increase in foliar nitrogen levels and protein synthesis. In addition, there was an improvement in photosynthetic parameters, indicating that foliar fertilization with molybdenum is a viable strategy not only for improving the nutritional status of the plant, but also a technique that stimulates carbon metabolism.

In view of this, foliar fertilization is an efficient and quickly applied management practice and aims to complement soil fertilization and improve crop performance in the field (FERNÁNDEZ et al., 2015). The adequate supply of nutrients can favor plant growth and development, in addition to improving the synthesis of photoassimilates and, consequently, enhancing grain filling and crop productivity (FAGERIA et al., 2009; NAVA et al., 2011; OLIVEIRA et al., 2019).

ILSA Foliar Fertilizers

As we saw in the text, foliar fertilization has the purpose of complementing soil fertilization and providing nutrients quickly and in specific situations, in order to avoid possible deficiencies. ILSA's foliar fertilizers combine the organic matrix GELAMIN^® with mineral sources of macro and micronutrients. We saw in the text that one of the disadvantages of applying foliar fertilizers is the use of poorly formulated products that can cause damage to the leaves and not supply the nutrients adequately to the plants. In order to achieve excellence in the formulation of its fertilizers, ILSA chooses to use formulation processes that maintain the characteristics of the active and highly available nutrients.

The GELAMIN matrix^® is obtained by the process of enzymatic hydrolysis, where the long polypeptide chains of proteins are cut by the action of water and selected stereoselective enzymes, without the addition of chemical substances that could reduce the quality of the products. FCEH technology^® from ILSA allows obtaining homogeneous, stable fertilizers with high miscibility, increasing the efficiency of foliar absorption of nutrients by plants.

In its portfolio, ILSA has a complete line of fertilizers to meet different needs and meet all situations that occur in crops.

References:

CARVALHO, SJP Weed desiccation with glyphosate herbicide associated with nitrogen fertilizers. DOCTORAL THESIS. “Luiz de Queiroz” College of Agriculture. Piracicaba-SP. 116p. 2009.

CERETTA, CA; SILVA, LS da; PAVINATO, A. Fertilization management. In: NOVAIS, RF et al. (Ed.). Soil fertility. Viçosa: SBCS, p. 851-872. 2007.

FAGERIA, NK; FILHO, MPB; MOREIRA, A.; GUIMARÃES, C.M. Foliar fertilization of crop plants, Journal of Plant Nutrition, v. 32, n. 6, p. 1044-1064, 2009.

FAQUIN, V. Mineral Nutrition of Plants. Federal University of Lavras – UFLA Foundation for Support of Teaching, Research and Extension – FAEPE Lavras – MG. 2005.

FERNÁNDEZ, V.; SOTIROPOULOS, T.; BROWN, P.; RODELLA, AA Foliar fertilization: scientific foundations and field techniques. 150p. 2015.

KIRKWOOD, RC Recent developments in our understanding of the plant cuticle as a barrier to the foliar uptake of pesticides. Pesticide Science, v.51, n. 1, p. 69-77, 1999.

MOCELLIN, Ricardo SP. Principles of foliar fertilization. Canoas: Omega Fertilizers Ltd., 2004.

NACHTIGALL, Gilmar R.; NAVA, Gilberto. Foliar fertilization: facts and myths. 2010.

NAVA, IA; GONÇALVES-JÚNIOR, AC; VALDIR, LGVL; NACKE, H.; SCHWANTES, D. Agroeconomic effect of formulated fertilizers containing zinc from different commercial brands on soybean cultivation in a Red Latosol. Scientia Agraria Paranaensis, v. 10, n. 3, p. 32-34, 2011.

OLIVEIRA, SM; JÚNIOR, CP; LAKE, BC; ALMEIDA, REM; TRIVELIN, PCO; FAVARINI, JL Grain yield, efficiency and the allocation of foliar N applied to soybean canopies. Scientia Agricola online, v. 76, no. 4, p. 305-310, 2019.

OLIVEIRA, Sirlene Lopes de. Foliar fertilization with molybdenum improves photosynthetic metabolism and increases soybean and corn productivity. Faculty of Agricultural Sciences, UNESP, Botucatu Campus. 2021.

REIS, Lucas Inocêncio Pinto dos. Foliar nitrogen fertilization on pasture production: literature review. Federal University of Tocantins. 2021.

TAIZ, L.; ZEIGER, E. Plant physiology. 6th ed. Porto Alegre: Artmed. 848p. 2017.

Authors

Agr Eng. Dr. Angélica Schmitz Heinzen

Agricultural Eng. Msc. Thiago Stella de Freitas