The supply and absorption of the substances required during the growth of the crop is called nutrition. On the basis of studying the law of plant nutrition, people use fertilization to improve the environmental conditions of plant growth and improve production efficiency. Plant nutrition is the theoretical basis for fertilization. Rational fertilization should be considered in accordance with the principles of plant nutrition and the nutritional characteristics of crops, combined with climate, soil and other cultivation measures. Only fertilization under correct guidance can significantly increase yield, improve quality, and protect the environment. Conversely, blind fertilization often does not increase production, and wastes resources, causing losses and harm.
Essential nutrients for crops
Although most of the elements that make up the earth's crust can be found in different crops, not every element is necessary for the crop. In 1939, scientists proposed three criteria for determining essential nutrients for crops:
- This element is indispensable for the growth and development of all crops. Without this elemental crop, life history cannot be completed.
- In the absence of this element, the crop will exhibit a unique condition that will only disappear after the element has been replenished.
- This element must be directly involved in the metabolism or composition of the crop, acting directly on the crop rather than improving the indirect effects of the crop's growing environment. According to the above criteria, 16 species of mineral elements necessary for crops have been identified.
Crop essential nutrient grouping
According to the crop's need for these nutrients, they are divided into two categories.
- A large number of elements, crops require a large amount of such elements. They account for about a few thousandths to a few tens of thousands of objects, including carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, and the like. Among them, carbon, hydrogen and oxygen come from air and water, but the effective supply of nitrogen: phosphorus and potassium in the soil is small, and the demand for crops is large. Therefore, these three nutrients are often lacking in the soil, and it is necessary to satisfy the crop by fertilization. Demand, so called nitrogen, phosphorus, potassium as the "three elements of fertilizer." Calcium, magnesium, and sulfur are sometimes further classified into medium-sized nutrients.
- Trace elements and trace elements account for about a few thousandths to a few hundred thousandths of the dry weight of crops. They are iron, boron, manganese, zinc, copper, molybdenum, chlorine and the like. Crops require very little of these elements, but when they are lacking, the crops cannot grow normally. For example, when the corn is deficient in zinc, it exhibits “white seedling diseaseâ€. When it is severe, the tassels are not stalked; when the rape is deficient in boron, the seedlings die, and the lighter presents “flowersâ€. It is not true; but if the trace elements are applied excessively, it will be harmful to the crops and even cause death.
General function of essential nutrients for crops
The nutrient effects of 16 essential nutrients in crops have their own characteristics. They are divided into four groups according to their biochemical and physiological functions in plants:
- The first group includes carbon, hydrogen, oxygen, nitrogen, and sulfur. They are the main constituents of organic matter and an essential element of the atomic group in the enzymatic reaction. Carbon, hydrogen, oxygen, etc. are assimilated to form organic matter in photosynthesis, and the process of nitrogen and sulfur assimilation is also the basic process of metabolism.
- The second group includes phosphorus, boron, and silicon. They are absorbed by plants in the form of inorganic ions or acid molecules, and can be esterified with a hydroxy compound of a plant to form a phosphonate, a borate or the like. Phosphonates are involved in energy conversion.
- The third group includes potassium, sodium, calcium, magnesium, manganese and chlorine. They are absorbed by plants in ionic form and are present in the sap of the cells in ionic form or adsorbed on non-diffusing organic ions. The main functions are: regulating cell osmotic pressure, activating enzymes, or becoming a coenzyme of enzymes to maintain the stability and selectivity of biofilms.
- The fourth group includes iron, copper, zinc and molybdenum. They are mainly present in the ligand in the form of a ligand, which constitutes a prosthetic group of the enzyme. In addition to molybdenum, it is often absorbed in the form of a chelate or a chromium compound. They pass electrons through changes in atomic valence.
The specificity and comprehensive function of crop nutrient function
The nutrients required for crops form complex interrelationships between crops, and these interrelationships are mainly expressed in equally important and irreplaceable relationships. The nutrients necessary for crops are equally important in crops regardless of the quantity, which is irreplaceable. This is called “the same important rate and irreplaceable rate of nutrient elementsâ€. Although the various nutrients in the crops are disparate in summer, they all bear some important and specific effects. Because of their role, specificity, the special role of each essential nutrient element is not replaced by any other nutrient element.
As science develops, people recognize the effects of interactions between certain nutrients. Often, without increasing the amount of fertilizer applied, as long as the fit is appropriate, there will be obvious effects. While emphasizing the unique and specific role of various nutrients, it does not exclude the combined effects of various nutrients. In fact, multiple nutrients work in synergistic conditions. .
Crop nutrient deficiency or excessive symptom recognition
In agricultural production, crops often affect the normal absorption of certain elements by crops due to soil factors and artificial over-application of chemical fertilizers, resulting in the lack or excess of nutrients. In cultivation, the cause of the disease can be determined according to the physiological abnormalities exhibited by the crop, and corrected in time to restore the normal growth of the crop. The symptom retrieval of various crop nutrient elements is shown in Table 1-1. '
- In the case of excessive nitrogen, when the nitrogen supply is too much, the chlorophyll is formed more and the leaves are dark green. The plants are long and greedy. Protein synthesis consumes a large amount of carbohydrates, and the cellulose, pectin and other substances that make up the cell wall are reduced, the cell wall is poorly developed, thinned, and easy to fall.
- Phosphorus hypertrophy, when the phosphorus supply is too much, because the plant's respiration is too strong, consume a lot of carbohydrates and energy, so that the cereal crops have no effective tillering, the heading is not neat, the empty mites increase; the leaves are thick and dense, the reproductive organs Premature development, stem and leaf growth is inhibited, and vegetative bodies are small. Low Yield. Excessive absorption of phosphorus in rice leads to a decrease in silicon absorption, which causes rice to suffer from rice blast. Because water-soluble phosphate forms compounds with low solubility in trace elements such as iron, zinc and manganese in the soil, it reduces the effectiveness of these elements. Sex, which may induce the occurrence of zinc deficiency, iron deficiency and manganese deficiency in plants.
- Excessive potassium, when potassium is used in excessive amounts, due to ion imbalance, it will affect the absorption of other cations, especially magnesium and calcium, causing the lack of calcium and magnesium in crops.
This article URL: Introduction to crop nutrition common sense and fertilization principles
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