What types of foliar fertilizer formulas are there? What functions does each have?

Foliar fertilizer is a fertilizer intended for absorption through the leaves, applying the nutrients needed by crops directly to the leaf surface, and is called foliar fertilizer. Foliar fertilizer is a type of fertilizer in which nutrient elements are applied to the leaf surface of crops and exert their basic functions through absorption by the leaves. Plant leaves have upper and lower epidermal layers made up of epidermal cells. On the outer side of the epidermal cells there is a cuticle and wax, which can protect the mesophyll cells beneath the epidermal tissue in carrying out photosynthesis, respiration and other functions without being affected by changes in adverse external conditions. The leaf surface also has many tiny stomata, which perform the function of gas exchange.

Classification of foliar fertilizer products 

According to different classification standards, the foliar fertilizers commonly used at present can be divided into the following types.     

1. By product form: can be divided into two types, solid (powder, granules) and liquid (clear liquid, suspension). 

3. By composition: can be divided into macronutrient, secondary nutrient and micronutrient foliar fertilizers, and water-soluble foliar fertilizers containing amino acids, humic acid, alginic acid, sugar alcohols, etc.     

3. By function: can be divided into two major categories, nutritional type and functional type. Nutritional foliar fertilizer is formulated from one or more of the macro, secondary and micro nutrient elements, and its main role is to provide and supplement crop nutrition in a targeted way and improve crop growth; functional foliar fertilizer is made by mixing inorganic nutrient elements with plant growth regulators, amino acids, humic acid, alginic acid, sugar alcohols and other biologically active substances, or fungicides and certain other beneficial substances. Among these, the various biologically active substances have a stimulating effect on plant growth, pesticides and fungicides have the effect of preventing diseases and insect pests, and the beneficial substances also have a stimulating and improving effect on crop growth and development. Therefore, this type of foliar fertilizer combines the functionality of certain additives with the supplementation of inorganic nutrient elements, thereby achieving a mutually synergistic and promotive effect. 

Functions of foliar fertilizer

1. Macronutrient foliar fertilizer 

This type of foliar fertilizer contains one or more of the three elements nitrogen, phosphorus and potassium. Among these, nitrogen fertilizer generally uses amide nitrogen, ammonium nitrogen, nitrate nitrogen or amino acids and other organic nitrogen sources. The product raw materials generally selected are urea, ammonium nitrate, potassium nitrate, ammonium sulfate, ammonium chloride, nitric acid, amino acids, etc.; phosphorus sources mainly use orthophosphates, metaphosphates, polyphosphates, etc., and in production potassium dihydrogen phosphate, dipotassium hydrogen phosphate, ammonium phosphate (monoammonium phosphate, diammonium phosphate), phosphoric acid and certain metaphosphates and polyphosphates, etc. are generally selected; potassium fertilizer generally uses potassium nitrate, potassium dihydrogen phosphate, potassium sulfate, etc. as raw materials for foliar fertilizer products. 

2. Secondary nutrient foliar fertilizer 

Generally refers to foliar fertilizer containing components such as calcium, magnesium and silicon. Among these, calcium fertilizer mainly uses water-soluble inorganic calcium salts and chelated calcium, and the product raw materials can be calcium chloride, calcium nitrate, calcium ammonium nitrate, calcium acetate, and calcium chelated with EDTA, citric acid, amino acids, sugar alcohols and other organic substances; magnesium fertilizer mainly uses water-soluble inorganic magnesium salts, generally magnesium chloride and magnesium sulfate are selected; water-soluble silicon fertilizer mainly uses sodium silicate (mainly sodium metasilicate and sodium metasilicate pentahydrate) as the silicon source. Because it is alkaline and readily reacts with calcium, magnesium, zinc, iron and other ions to form flocculent precipitates, it is therefore generally used alone in foliar fertilizer. 

3. Micronutrient foliar fertilizer 

In China's agrochemical market there are generally two types, single-element type and compound-element type. Generally, readily soluble inorganic salts and chelated trace elements, etc. are selected as raw materials.

Functional foliar fertilizer 

1. Plant growth regulator type foliar fertilizer 

In addition to nutrient elements, this type of foliar fertilizer has substances added that regulate plant growth. Generally, growth-promoting regulator types such as gibberellin, triacontanol, sodium nitrophenolate, DA-6, naphthaleneacetic acid (sodium) are used as the main components, and the main role is to regulate the growth and development of crops, suitable for use in the early and middle stages of crop growth. 

With the development of the foliar fertilizer market, the application of plant growth regulators has achieved tremendous development. Because of characteristics such as obvious effects, quick results and low cost, they have attracted the attention of many manufacturers. However, we suggest that manufacturers, when applying regulators, should consider differences in crop, region, climate and farmland management, and not blindly add regulators, so as to achieve a genuine yield-increasing effect. It is even more important to choose products of guaranteed quality and prevent adverse effects on crops. 

At present, the regulators commonly used in production are the several types above. 

2. Foliar fertilizer containing natural active substances 

This type of foliar fertilizer generally contains fermentation or metabolic products extracted and processed from natural substances (such as seaweed, straw, animal hair, peat, weathered coal, etc.), producing substances such as amino acids, humic acid, nucleic acid, alginic acid and sugar alcohols. These substances have functions such as stimulating crop growth, promoting crop metabolism and improving the crop's own stress resistance. 

(1) Amino acid type foliar fertilizer 

Amino acids have two sources, plant and animal. Plant-source amino acids mainly include fermentation products of soybean, oilseed meal, etc., as well as by-products of soybean products and vermicelli; animal-source amino acids mainly include leather, hair, fishmeal and slaughterhouse by-products, etc. The processes for converting raw materials into amino acids also differ. The simplest is the acid hydrolysis process, commonly using a hydrochloric acid solution at a concentration of 4—6moI/L, hydrolyzing with the material in proportion for a certain time, then neutralizing with ammonia or other alkaline substances, and after adjusting the PH value it is the stock solution; the more complex one is the biological fermentation method, commonly using a composite microbial flora to ferment the material under certain conditions for 4—6 weeks, and after the fermentation liquid is refined, it is processed into water-soluble fertilizer containing amino acids. 

At present, the amino acid fertilizers sold on China's market are mostly compound amino acids obtained by acid hydrolysis of soybean meal, cottonseed meal or other ammonia-containing agricultural by-products, and are mainly pure plant proteins. Such amino acids have good nutritional effects, but relatively poor biological activity; whereas amino acids produced by biological fermentation mainly involve enzymatic hydrolysis and biodegradation of proteins, and fermentation produces some new active substances, such as nucleotide-like substances, indole acid, gibberellic acid, fulvic acid, etc., which have strong biological activity and can stimulate crop growth and development, increase enzyme activity and enhance disease resistance and stress resistance. They all have a certain effect on rooting, promoting growth, and protecting flowers and fruits. 

(2) Alginic acid type foliar fertilizer 

The active substances of seaweed fertilizer are extracted from natural seaweed. The main raw material is fresh seaweed, generally large economic algae, such as sargassum, sea bladder algae, kelp, etc. Its production processes include chemical extraction, fermentation, low-temperature physical extraction, etc. Generally speaking, seaweed extracts treated by physical methods have higher plant activity and are rich in vitamins, seaweed polysaccharides and various plant growth regulators, such as auxins, gibberellins, cytokinin-like substances, polyphenolic compounds and antibiotic substances, etc., which can stimulate the production of active factors in the crop and regulate the balance of endogenous hormones. 

At present, the development of seaweed agricultural products has gone through 3 stages: namely rotted seaweed——algae ash (powder)——seaweed extract liquid. The extraction process of seaweed extract is roughly as follows: by screening suitable fresh seaweed varieties, using mechanical methods, without contact with any chemical reagents, without undergoing high temperatures exceeding 45 ℃, without any dehydration and freezing, only through high-pressure foaming to break the cell walls and release the contents, and concentrating to form a seaweed essence concentrate, thereby greatly retaining the natural active ingredients of the seaweed.

In China, there is preparation of seaweed organic fertilizer through the fermentation method, with the process as follows:

① Fermentation: algae (containing an appropriate amount of water) + biological microbial strains, mixed evenly, placed in a fermentation tank for fermentation, with appropriate adjustment according to the tank temperature (including water, air, temperature, etc.);

② Extraction: to the fermented product, add an extraction agent, then add a certain amount of water and stir thoroughly and evenly.

③ Dehydration: dehydrate the extract, add nitrogen, phosphorus, potassium and trace elements to the liquid part, and after concentration it becomes liquid fertilizer; the solid part is dried, then crushed and granulated into organic fertilizer. 

There are three methods of using seaweed fertilizer in China: foliar spraying, soil application and seed soaking. Among these, foliar application is the most effective and broad-spectrum method of use. It can stimulate root development and the absorption of nutrients, and significantly improve the crop's resistance to disease, salinity and alkalinity, low temperature and other stresses.