Nitrogen: Often called the element of life.
Nitrogen is an important element that constitutes living substances, and it is also an important element that affects the metabolic activities and growth results of citrus plants.
Nutritional effects of nitrogen
(1) Nitrogen is the main component element of protein: The average content of nitrogen in protein is 16%~18%. During the growth and development of crops, proteins must be involved in the growth and division of cells and the formation of new cells. When higher plants are deficient in nitrogen, the formation of new cells is blocked, resulting in slow plant growth and development, or even growth stagnation. Protein is also important because it is the form of life in organisms. If there was no nitrogen and no protein, there would be no life.
(2) Nitrogen is a component of nucleic acids and nucleoproteins: Nucleic acid is the basic substance for plant growth, development and life activities. Nucleic acid contains 15% to 16% nitrogen. Both ribonucleic acid and deoxyribonucleic acid contain nitrogen. Nucleic acids are usually combined with proteins in cells and exist in the form of nuclear proteins. Nucleic acids and nuclear proteins are abundantly present in cell nuclei and plant apical meristems, and play special roles in plant life and genetic variation. RNA is the template for protein synthesis, and DNA is the genetic material that determines the biological characteristics of crops. Both DNA and RNA are transmitters of genetic information. Therefore, crops cannot sustain life without nitrogen.
(3) Nitrogen is a component element of many enzymes: Enzymes are biological catalysts in biochemical and metabolic processes in plants. The main component of enzymes is protein. The direction and speed of many biochemical reactions in plants are controlled by enzyme systems. Usually, one or several corresponding enzymes must participate in each biochemical reaction in the metabolic process. Without the corresponding enzymes, it is difficult for the metabolic process to proceed smoothly. The enzyme itself is a protein. Therefore, nitrogen often indirectly affects the growth and development of plants through enzymes. Therefore, nitrogen supply status is related to the conversion process of various substances and energy in crops.
(4) Nitrogen is a component element of chlorophyll: Chlorophyll is the factory that produces "food" in crop leaves. It uses absorbed solar energy, carbon dioxide in the air and moisture in the soil to synthesize organic substances. The content of chlorophyll often directly affects the rate of photosynthesis and the formation of photosynthetic products. When green crops lack nitrogen, the chlorophyll content in the body decreases, the leaves turn yellow, the intensity of photosynthesis weakens, and the photosynthetic products decrease, thus significantly reducing crop yields. Therefore, it is unimaginable to not have nitrogen involved in the growth and development of green plants.
(5) Nitrogen is a component of certain vitamins and alkaloids: For example, vitamin B1, vitamin B2, vitamin B6 and alkaloids (nicotine, theophylline, etc.) all contain nitrogen. They are components of coenzymes and participate in the metabolism of crops.
(6) Nitrogen is a component of some plant hormones: Such as auxin and cytokinin, etc. contain nitrogen.
(7) Nitrogen can improve the nutritional value of crops: In particular, it can increase the protein content in seeds and improve the nutritional value of food.
The form of nitrogen
A large amount of nitrogen in the plant exists in organic form, and there is a small amount of ammonium nitrogen and nitrate nitrogen in the roots. There are three types of nitrogen in soil: organic nitrogen, inorganic nitrogen and organic-inorganic nitrogen. Organic nitrogen accounts for about 90% of the total nitrogen content in soil. Organic nitrogen mainly refers to the nitrogen contained in animal and plant residues in the soil. They generally apply organic fertilizers, such as straw fertilizer returned to the field, animal residues, artificially applied human and livestock manure, etc. The content of organic nitrogen in the soil is closely related to the amount of organic matter applied and the content of soil organic matter. They carry nitrogen in the form of organic matter in the soil. This nitrogen mainly exists in the form of various amino acids, amino sugars, purines, pyrimidines, vitamins, etc., and most of it exists in the soil in solid form. The release of organic nitrogen depends on the decomposition of organic matter in the soil. After the decomposition of organic matter, nitrogen ions are released and converted into inorganic nitrogen. Organic nitrogen has long-lasting effects. Organic nitrogen mainly exists in the remains of animals and plants. The inorganic nitrogen content of total soil nitrogen only accounts for about 5%, mainly ammonium and nitrate, nitrite, ammonia, nitrogen and nitrogen oxides. Most of the ammonium nitrogen and nitrate nitrogen are easily absorbed and utilized directly by citrus and are available nitrogen.
Nitrogen and citrus
Citrus shoots and flowers contain the most nitrogen, so shoot shoots and flower and fruit development consume more nitrogen in spring. Citrus plants can accumulate more nitrogen in autumn and winter for shoot shoots and flowering in the following spring. Generally, the nitrogen content increases with the development of the flower and reaches the highest level when it blooms. The female and stamens are the organs with the most nitrogen in the flower. On the contrary, the nitrogen content in leaves decreases with flower development, that is, nitrogen in leaves is lost to flowers and fruitlets in spring. Early-blooming flowers contain more nitrogen and have a higher fruit-setting rate than later-blooming flowers. Within a certain range, the number of flowers and fruits is directly proportional to the nitrogen content in the citrus tree or leaves. During this period, the fruit setting rate is also high if the nitrogen content in the leaves is high, that is, more nitrogen is consumed during the development and growth of new branches, leaves and flowers in spring. Citrus can still absorb a considerable amount of nitrogen when the soil temperature is 9°C, that is, citrus-producing areas with higher soil temperatures in winter can absorb nitrogen throughout the year. However, most of the nitrogen is absorbed during the high-temperature period from spring to autumn when growth and activity are strong. The flowering and fruiting period in spring is often the period when the largest amount of nitrogen is absorbed in the whole year, indicating that more nitrogen fertilizers need to be supplied during this period. But not too much, based on the nitrogen content of mature leaves during the flowering and fruiting stage.
Citrus has a large demand for nitrogen. If nitrogen is sufficient, the roots, branches and leaves will grow strong, the leaves will be dark green, the flowers and fruits will be normal, the yield will be high, and the quality will be good. Nitrogen is stored in tissues, especially in leaves. Even if the increase is small, nitrogen has a great impact on the growth of branches, leaves and fruits. When the amount of nitrogen applied does not exceed the limit, as the amount of nitrogen applied increases, the nitrogen content of leaves and fruit yield will also increase. Before and after the plant blooms, a large amount of nitrogen is transferred from the leaves to the flower buds to meet the needs of flowering. Nitrogen has the effect of stabilizing and strengthening fruits and promoting the differentiation of flower buds. If a large number of leaves fall in winter and early spring, it will cause a large loss of nitrogen, affect the tree vigor and the development of flowers and fruits, and cause a reduction in yield. When the nitrogen content is within a certain range, the number of flowers, fruit set and yield of the plant are directly proportional to the nitrogen content in the tree.
Symptoms of nitrogen deficiency and excess nitrogen
Nitrogen deficiency:
(1) The growth of the plant is weakened, the new shoots are abnormally sprouted, and the branches and leaves are sparse and short.
(2) The leaves are thin, uniformly chlorotic, yellow, and dull. This symptom can be distinguished from other deficiency diseases. In severe cases, the leaves of the entire plant will turn yellow uniformly and fall off prematurely.
(3) There are few flowers and small fruits, or even no fruits. The peels are pale and smooth, and they often mature early.
(4) When there is severe nitrogen deficiency, dead shoots will appear, tree vigor will decline, and the crown will be bare.
Nitrogen deficiency causes old leaves to turn yellow and fall off prematurely
Nitrogen excess:
(1) The peel thickens, the juice decreases, and the soluble solids decrease.
(2) If too much urea is used, citrus leaves will be damaged due to the biuret in the urea.
(3) If the nitrogen content is too high, the branches will become elongated, the flower buds will be reduced, and the flowers and fruits will drop seriously.
(4) High nitrogen levels will produce more green-skinned fruits, but fewer wrinkled-skinned fruits, and fruit coloring will be delayed.
High nitrogen content and leggy branches.
Reasons for nitrogen deficiency
(1) The nitrogen content in the soil of citrus orchards is insufficient. Such as sandy soil, which is prone to nitrogen loss, volatilization and leakage, resulting in low nitrogen content; or soil with little organic matter, low maturity, and strong leaching, such as newly reclaimed red and yellow loam soil that has not been improved and matured.
(2) Related to climatic conditions. For example, in rainy citrus-producing areas, nitrogen is easily lost; nitrogen deficiency may occur in soil waterlogging or drought.
(3) Applying too little nitrogen fertilizer or applying fertilizer on the ground causes nitrogen loss.
(4) The previous year's cultivation and management were not in place, which affected the tree's nutrient storage. The following year, when the shoots were cropping and flowering and bearing fruit, the fertilizers were not kept up and there was a lack of nitrogen.
(5) Applying large amounts of undecomposed organic fertilizers can cause nitrogen deficiency due to microbial activity competing for nitrogen sources.
Methods to correct nitrogen deficiency
(1) Increase the application of quick-acting nitrogen fertilizer at the roots and combine it with phosphorus and potassium fertilizers to avoid antagonism between elements when a large amount of nitrogen fertilizer is applied. Apply more organic fertilizer. In addition, strengthen water management to prevent the soil from being too dry or too wet, so as to avoid underdevelopment of the root system, affecting absorption and resulting in nitrogen deficiency.
(2) Spray high-nitrogen fertilizer on the leaves, once every 5-7 days, and spray 2-3 times in a row.
