What is the principle of fertilization? What are the basic methods?

Part of plant components are obtained from air, part from water, part from soil minerals, and the insufficient part must be supplemented artificially. This is called fertilizer.

Fertilizers needed by plants can be divided into three types according to the number of elements needed: large amount fertilizer, medium amount fertilizer and trace amount fertilizer. From the experience of crop planting, it is known that the most restrictive elements for crop growth in general soil cultivation are nitrogen, phosphorus and potassium, which are usually called fertilizer.

Humans need to eat meat, vegetables and whole grains to grow normally, and plants also need food, but plants are inferior to humans, and their food is mainly inorganic minerals.

A plant grows from a small seed into a plant, and its constituent elements are obtained from soil and air. After drying the plants, analyze the constituent elements, as shown in Table 1.

Fertilizers needed by plants can be divided into three types according to the number of elements needed: macro-element fertilizers, medium-element fertilizers and trace-element fertilizers. Please refer to Table 2.

Table 2: Fertilizer Classification by Element Requirement

Basic principles of fertilization:

First, the minimum nutrition rate.

Although the amount of elements required for plant growth is different, in order to maintain normal growth, the amount of these elements must be balanced to a certain extent. As long as the proportion of one element is low, the growth of the whole plant is dominated by it, which is the nutritional law of the least plant growth. Therefore, there must be a concept of nutritional balance when fertilizing.

Second, the rate of diminishing returns.

According to the experience of crop cultivation, the most restrictive factors for crop growth in general soil cultivation are nitrogen, phosphorus and potassium, which are usually called fertilizer.

Assuming that nitrogen is the most scarce nutrient element in cultivated crops, the effect of fertilization to promote growth will be seen soon after nitrogen fertilizer is applied, but the plant growth will not increase at a fixed rate with the increase of nitrogen fertilizer, but will gradually decrease, and finally there will be no growth or even a decrease in yield when nitrogen fertilizer is applied again, which is the diminishing rate of fertilization returns. Therefore, when fertilizing, we should also have the benefit concept of fertilization and pay attention to correct fertilization. Excessive fertilization not only can't get the return of crop growth, but is in danger of obesity.

Third, the timing of fertilization should be coordinated with the stage of plant fertilizer demand.

The life process of plant development and growth can be roughly divided into three stages: vegetative growth stage, differentiation stage and reproductive growth stage, and the types and dosage of fertilizers required in each stage are different. To ensure the normal growth of plants, it is necessary to cooperate with the nutritional and physiological needs of plants and apply fertilizers in a timely and appropriate manner.

Relationship between plant growth and fertilizer

I. Nitrogen fertilizer (commonly known as foliar fertilizer)

Nitrogen fertilizer is an indispensable nutrient for the green part of leaves and stems of plants, especially for foliage plants and leafy vegetables, so it becomes foliar fertilizer.

● Types of nitrogen fertilizer

Nitrogen absorbed and utilized by plants are inorganic nitrate nitrogen (NO3-) and ammonium nitrogen (NH4++). As for organic nitrogen, such as urea, animal skin powder, bean cake and so on. It is also used as nitrogen fertilizer, but it can be absorbed and utilized by crops only after it is decomposed into nitrate nitrogen and ammonium nitrogen by bacteria in the soil. Therefore, the types and characteristics of nitrogen fertilizer are shown in Table 3.

Table 3: Types and characteristics of nitrogen elements

Whether nitrogen nutrition is suitable, insufficient or excessive in the process of plant growth can be judged by the chemical analysis value of plant nitrogen content, but it needs to be done by chemical analysis laboratory. General cultivation can judge the general situation of insufficient or excessive nitrogen fertilizer from the performance of plant growth, so the performance arrangement of insufficient or excessive nitrogen fertilizer affecting plant growth is shown in Table 4.

Table 4: Performance of insufficient or excessive nitrogen affecting plant growth

Second, phosphate fertilizer (commonly known as flower and fruit fertilizer)

Phosphorus is an essential element for the healthy growth of plants, well-developed roots, lush flowers and abundant fruits, so it is also called flower and fruit fertilizer.

● Types of phosphate fertilizer

Plants only absorb plasma phosphate, including H2PO4-,HPO42-and PO43-. The types of phosphate fertilizer are divided into inorganic phosphate fertilizer and organic phosphate fertilizer. Inorganic phosphate fertilizer can be divided into water-soluble phosphate fertilizer and ammonium citrate soluble phosphate fertilizer according to its dissolution characteristics. Organic phosphate includes organic phosphate such as rice bran and bean cake. The types and characteristics of phosphate fertilizer are shown in Table 5.

Table 5: Types and characteristics of phosphate fertilizer

Insufficient and excessive phosphate fertilizer is a common problem in plant growth. Phytochemical analysis is helpful to judge whether the phosphorus content is insufficient or excessive, and ordinary growers can judge from the surface of plant growth. The performance of insufficient or excessive phosphorus affecting plant growth is shown in Table 6.

Table 6: Performance of insufficient or excessive phosphorus affecting plant growth

Three, potash fertilizer (commonly known as root fertilizer)

Plants have a great demand for potassium, and plants need enough potassium for normal growth. Glucose synthesized by plant photosynthesis needs potassium to help transport and distribute to other sectors, or to synthesize starch or other carbohydrates.

In addition, potassium can promote the growth of root system, and the formation and development of root xylem are affected by potassium; Potassium can regulate water, maintain cell swelling pressure and increase the resistance of plants to low temperature environment; Potassium can also increase the resistance of plants to pests and diseases.

● Types of potash fertilizer

Plants only absorb potassium ions (K+), so water-soluble potassium nitrate, potassium sulfate and potassium chloride are the most commonly used potassium fertilizers, and water-insoluble potassium silicate also has commercial value. As for various plants, bean cakes and dried seaweed also contain water-soluble potassium, which is called organic potassium fertilizer according to its source. The types and characteristics of potash fertilizer are shown in Table 7.

Table 7: Types and characteristics of potash fertilizer

The potassium content of phytochemical analysis is helpful to judge whether the potassium content is insufficient or excessive, which can be judged by the performance of plant growth. The performance of insufficient or excessive potassium affecting plant growth is shown in Table 8.

Table 8: Performance of potassium deficiency affecting plant growth

Relationship between fertilizer absorption rate and plant growth and development

The absorption rate of fertilizer is closely related to the life process of plant development and growth, which can be divided into three stages: vegetative growth stage, differentiation stage and reproductive growth stage.

First, the vegetative growth period:

It is a growth stage of roots, stems and leaves of plants, during which plants develop from seeds to plants with lush leaves.

Second, the differentiation stage:

After the vegetative growth period, the leaves of plants flourish to a certain extent, that is, tissue differentiation begins, buds are bred, and flowers, fertilization and fruiting are prepared.

Third, the reproductive growth period:

It is the stage of flower growth, flowering, fertilization and fruiting.

Absorption rate of three elements in fertilizer

In the physiological process of plants from seed germination, rooting, lush foliage to flowering and fruiting, the amount of fertilizer needed to be absorbed and utilized at each stage is significantly different. If the total amount of nitrogen, phosphorus and potassium to be absorbed in the whole period is 100%, the percentage of each element absorbed in each growth stage is called fertilizer absorption rate.

During vegetative growth, plants need more nitrogen and potassium, but less phosphorus. In the differentiation stage, plants began to need more phosphorus, and the absorption reached a peak. At the same time, they still need to absorb more potassium, while the demand for nitrogen is gradually weakening. In the bud stage, flowering stage and fruiting stage of reproductive growth, the demand of plants for three elements is basically the same as that in the differentiation stage, and it is not until the plants enter the fruit maturity stage that they begin to reduce the demand for three elements.

Generally speaking, in the life of plants:

● Nitrogen demand: In the vegetative growth period, to grow roots, branches and leaves, a large amount of nitrogen is needed to synthesize protein to support the vigorous growth of roots, stems and leaves, so the nitrogen absorption rate reaches the peak during this period. After entering the differentiation stage until the fruiting stage, it is basically the transfer and redistribution of nitrogen in the plant, so the nitrogen absorption rate gradually decreases.

● Demand for phosphorus: Plants enter the differentiation stage from vegetative growth stage. In the process of flower bud differentiation, bud formation, flowering, fertilization and fruiting, cell division and differentiation to form new tissues need a lot of energy in plants, such as ATP and ADP, and phosphorus is also needed to synthesize genetic materials such as nucleic acid RNA and DNA. Therefore, the absorption rate of phosphorus reached its peak at flowering stage and entered fruiting stage, so phosphorus was no longer needed, and the absorption rate decreased rapidly.

● Demand for potassium: Because potassium is always distributed in cells and tissues in the form of potassium ion (K+) in plants, it does not directly participate in the composition of cells and organs such as roots, stems, leaves, flowers and fruits. Sugar produced by photosynthesis needs to be transported, distributed and converted into carbohydrates such as starch in plants, and nitrate is reduced and converted into protein, so the demand for potassium in plants is relatively average throughout their lives. Generally speaking, the demand trend of nitrogen is the same as the vegetative growth period. In the vigorous growth period of roots, stems and leaves, the absorption rate of potassium reached the peak, and decreased slightly in the germination and flowering stages, and then decreased gradually and obviously in the fruiting stage.

See figure 1 for the relationship between fertilizer absorption rate and plant growth stage.

Basic methods of applying three elements of fertilizer

It has been explained that the absorption rate of three elements in fertilizer varies with the demand of each growth stage, so the plan of topdressing and supplementing three elements should make the demand period and absorption rate of three elements match ideally.

In fact, the general fertilization method is to fertilize the soil. The three elements of the fertilizer are dissolved by water, enter the soil with the water, reach the active range of the root circle, and then are absorbed by the roots and enter the plants. Therefore, there is an intermediary effect of soil medium between fertilizer elements and plant roots.

The surface of soil particles is negatively charged. In order to neutralize electricity, many positively charged cations such as calcium, magnesium and iron are adsorbed on it. These ions can easily combine with phosphate anion of phosphate fertilizer to produce low water solubility calcium phosphate, magnesium phosphate and iron phosphate. Therefore, the fluidity of phosphate fertilizer in soil is poor, that is, it is not easy to move long distances with soil moisture and distribute to the whole rhizosphere. Therefore, phosphate fertilizer is usually used as base fertilizer in systems with soil as cultivation medium.

As for nitrogen fertilizer and potassium fertilizer, they are easily soluble in water and move to the root zone with soil moisture, so they can be applied in stages and parts. Usually, two-thirds of the nitrogen and potassium fertilizers needed for the whole plant growth cycle are mixed into the soil during the basal fertilizer period, and the remaining 1/3 is applied as topdressing during the vigorous plant growth period. Batch fertilization is obviously extensive and not the most suitable scheme for plant development. Therefore, the development of slow-release fertilizers and controlled-release fertilizers that meet the requirements of labor-saving, time-saving and absorption rate is still a subject that fertilizer industry needs to work hard.

If it is a hydroponic cultivation system, the roots of plants are in direct contact with fertilizer elements, and the fertilizer elements that plants need to absorb at various growth stages can match the supply and supply frequency of water-soluble fertilizers more accurately.