During the plants’ vegetation period (ontogeny), nutrients are absorbed unevenly. A rational fertilization system should consider the life cycles of plants’ needs for nutrients and provide them promptly in the required quantity and ratio in the most digestible forms.
Insufficient supply of one or another element in some periods of life leads to a decrease in the harvest quantity and quality.
During the plants’ vegetation periods, they single out periods different in the nutrients’ absorption. These are: the critical period, when plants receive a small number of nutrients, but their lack impairs the growth and development, and the period of maximum absorption when plants absorb them in a larger amount.
For many plants the critical period (especially about phosphorus) is when the seeding appears. During this period, synthetic processes take place in plants intensively, but the root system is still weakly developed. Even if in the following growth stages phosphorus nutrition is sufficient, it will not make the situation any better — the yield won’t be high. Therefore, more phosphorus should be provided when feeding the plants, in comparison to nitrogen and potassium at the beginning of the growing season. For this purpose phosphorus fertilizers are applied in small doses to the rows during sowing. Some crops (for example, cereals, beets and potatoes) need all the main nutrients to be applied during sowing. These main nutrients are: nitrogen, phosphorus and potassium.
In cereals, the establishment and differentiation of reproductive organs begin in the period of 3–4 true leaves. Lack of nitrogen during this period leads to a decrease in the number of spikelets in a spike and a reduction in the yield. Therefore, this deficiency cannot be corrected by ordinary nitrogen feeding.
It’s also worth noting that the duration of the nutrition period, that is the time during which plants absorb nutrients from the environment, doesn’t always coincide with the vegetation period. At the initial stages of life, they use nutrients from germinating seeds or from tubers or roots. Many plants stop absorbing nutrients from the outside at the end of the vegetation period but continue to reuse those that have been absorbed earlier.
Agricultural crops differ significantly in terms of the feeding period duration. For example, beets, potatoes, corn, peas, lupins, clover, and other crops absorb nutrients throughout the vegetation period, while in barley, the feeding period takes place during the first 50–60 days, although the vegetation season lasts 80–90 days.
The intensity of the nutrients’ absorption by plants in different vegetation periods is not the same. Each crop has its own periods of intensive absorption. For example, herbs, beets, corn, and sunflowers are distinguished by a long period of nutrients’ absorption, which continues almost until the end of their growing season. All grain crops (except corn), as well as flax, early potatoes, and some vegetable crops, have a short period of main nutrients’ absorption.
For example, cabbage absorbs more nutrients during the head formation. During the second month of life, sugar beet absorbs 50 times more nitrogen, 15 times more phosphorus and 60 times more potassium than during the first month.
Flax is most sensitive to the rates of nitrogen nutrition from the fir-tree phase to budding and cereal crops — during the leaf apparatus formation and reproductive organs differentiation, that is, from the phase of emergence into the tube until the beginning of earing. Sugar beet needs increased potassium nutrition during the period of sugar accumulation.
Cucumber is picky about nitrogen nutrition during the leaf apparatus formation and about phosphorus nutrition before flowering. It needs an increased supply of nitrogen and potassium during the fruiting period.
The need of most plants for nitrogen before the beginning of fruiting decreases and the value of phosphorus and potassium in plant nutrition increases. In general, during fruiting, the absorption of nutrients decreases and at the end of the growing season, the vital activity of plants mainly occurs through the reuse of previously accumulated nutrients.
The peculiarities of the nutrients absorption at different phases of the vegetation period must be taken into account when developing a crop fertilization system, which usually includes three methods of fertilizers application at different time periods: main, row and top feeding. The main application of fertilizers before sowing should ensure the nutrition of plants throughout the vegetation period, therefore the full rate of organic and the larger part of mineral fertilizers are usually applied. The purpose of fertilizers application to the rows is to support the plants in the first 10–20 days after the seedlings’ emergence. For this purpose, easily soluble forms of phosphorous or complex fertilizers are used. During the period of maximum nutrients absorption by plants, root and foliar fertilization are carried out.
Nowadays growing vegetables and other agricultural crops in protected soil conditions has expanded. At the same time, it’s possible to increase the productivity of plants using periodic feeding. It’s known that plants have annual, seasonal and daily rhythms; in addition, pulsatile rhythms with periods from several hours to several seconds are observed. The periodic feeding method is especially promising for hydroponics and aeroponics, as it allows to significantly increase the productivity of crops without increasing the cost of mineral nutrition. What matters the most during growing plants in artificial conditions is the composition, concentration of the nutrient solution, and the mode of its application, which is to change during the growing season. Temporarily suspended income of the nutrients’ supply from the external environment during certain periods can cause intensive root development. By supplying water instead of a nutrient solution, the plants can be starved, that is, the process of fruiting will be stimulated and the effect of early maturing will be gained.
Well, after all the explanations, let’s talk about the critical periods of growth and development stages that are relative to the increase in plant consumption of nutrients:
- BBCH 00-09 (Emergence of plant seedlings). In this phase, we pay attention to the energy of germination and the appearance of friendly seedlings. As while growing the crops, the plant isn’t always provided with all nutrients, which then affects the quality of the seeds. When developing in the endosperm, there is not enough food for germination. Therefore, the seeds are tested for germination in laboratory conditions and the seed is treated with fertilizers to increase the energy of germination.
- BBCH 13-19 (Leaf development). Here we pay attention to the fact that most plants form the beginnings of reproductive organs and the number of flowers is determined during this phase.
- BBCH 31-39 (Stem extension). It’s also called the “great critical period”. The sensitivity of plants to the lack of nutrients, water and light increase sharply. Under unfavorable conditions, productive shoots are reduced. Due to the lack of nitrogen, phosphorus and potassium, the productivity of individual plants decreases. Fertilizer microelements participate in many biochemical reactions, they become part of enzymes, vitamins, hormones and other biologically active substances, which activate the growth of biomass and boost the efficiency of photosynthesis and resistance of plants to adverse environmental conditions.
- BBCH 51-59 (Buttonization). This phase is characterized by the development of flowers, the formation of high-quality receptacles of pistils and anthers. This will affect fertilization and the amount of ovary.
- BBCH 71-79 (Fruits and seeds formation). Qualitative indicators of the future harvest are being formed. Foliar treatments also extend the period of functioning of the photosynthetic apparatus and the leaves’ life-span as of the main assimilates’ donor. And this contributes to the absorption of more nutrients, improving the quality and increasing the weight of the grain.
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