I. Apple tree nutrients and their physiological functions
a) Essential nutrients
The plant is a natural chemical plant. Since the birth of plant life, it has undergone complex and delicate chemical reactions at every moment in its body. Using the simplest inorganic materials as raw materials to synthesize various complex organic substances.
Under light conditions during the day, the plant sucks in carbon dioxide from the atmosphere through the stomata in the leaves, generates carbohydrates with the water absorbed in the roots, and releases oxygen and heat. This process is called photosynthesis. Photosynthesis forms carbohydrates. Carbohydrates further synthesize starch, fat, cellulose or amino acids, proteins, protoplasms or nucleic acids, chlorophyll, vitamins and other essential substances for life. Body to.
Graphically speaking, plants are producers, animals are consumers, and humans are the biggest consumers.
Of course, to form the plant body, other chemical elements are also needed. In general, all the plants need 16 elements. They are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulfur, calcium, magnesium, boron, iron, copper, zinc, manganese, molybdenum, chlorine. The other four elements, sodium, cobalt, vanadium, and silicon, are not required for all plants, but are necessary for certain plants, and their lack of them.
Let us first familiarize ourselves with the symbols of these elements. Carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), boron (B), The 16 elements of iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), molybdenum (Mo), and chlorine (Cl) are currently considered as essential elements of plants. Here we focus on them.
Now we classify these 16 elements. The elements that make up the plant protein and further synthesize the protoplasm include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), and sulfur (S). If the plant body is burned, carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) will become gaseous oxides and go into the air. The remaining 12 other elements will turn to the naked eye. Visible solid oxides, often referred to as plant ash.
The three elements of carbon (C), hydrogen (H), and oxygen (O) can be obtained from carbon dioxide and water, converted into simple carbohydrates through photosynthesis, and further formed into starch, cellulose or amino acids, proteins, and protoplasm. , It may also generate other substances. It is generally believed that these elements are non-mineral elements. People have less control over these elements. The water needed for plants generally comes from precipitation, surface water, and groundwater. In times of drought and water shortage, people can supplement some of the water through irrigation. When waterlogging is done, a part of the excess water is drained to divert canal to regulate the water needed by the plant to a certain extent. Carbon dioxide comes from air. People can't control the supply of carbon dioxide to open-air crops, except that they can supplement some of the carbon dioxide that plants grow in greenhouses. Therefore, they are generally not considered when considering nutrients.
The remaining 13 elements come from the soil and are called mineral nutrients. People can regulate their supply by fertilizing. This is the focus of our discussion in the future. According to their content in the plant body, they can be roughly divided into three categories:
A large number of elements include nitrogen (N), phosphorus (P), and potassium (K).
The middle elements include sulfur (S), calcium (Ca), and magnesium (Mg).
The trace elements are boron (B), iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), molybdenum (Mo), and chlorine (Cl).
This classification does not mean that some of the elements that are important are not important. They are equally important in plants and are indispensable. No matter what kind of element is lacking, it will cause harm to plant growth. Similarly, an excess of an element can also be harmful to plant growth because an excess of one element means a shortage of other elements. Here we will discuss a series of questions about their role in the plant, the laws that the plant needs for them, and what nutrients they can get from the fertilizer.
1, nitrogen
Most of the arable land in China is deficient in nitrogen fertilizer, and nitrogen is often the dominant factor limiting agricultural production. Therefore, nitrogen fertilizers can generally increase production.
1) The physiological function of nitrogen
(1) Nitrogen compounds in crops are mainly present in protein form.
(2) Nitrogen is also a constituent of nucleic acids.
(3) Nitrogen is also a component of many enzymes in plants.
(4) Nitrogen also participates in the composition of chlorophyll.
(5) Some vitamins in plants such as B1, B2, B6, and PP also contain nitrogen.
2) Symptoms of nitrogen deficiency or excess
Nitrogen nutrition conditions have a significant effect on the growth and development of fruit trees. Nitrogen deficiency significantly inhibited the growth of aerial parts and roots. Nitrogen deficiency had the greatest impact on leaf development. The leaves were small and erect, with small angles to the stems, pale green leaves, and pale yellow when severe. The chlorosis leaves are uniform in color and generally do not show spots or variegated spots. Because the nitrogen compounds in crops are highly mobile and can be transferred from old leaves to young leaves, the symptoms of nitrogen deficiency usually begin with the old leaves and gradually extend to the upper young leaves. This is different from the yellowing of the drought-fed leaves, which almost yellowed both at the upper and lower leaves of the same plant.
The roots of nitrogen-deficient crops were initially whiter and slender than normal, but the amount of roots was small; in later stages, the roots stopped growing and appeared brown.
Excessive nitrogen can easily promote the formation of large amounts of protein and chlorophyll in the plant, making the nutrients grow and grow, the leaf area increases, the leaf color is dark green, and the leaves are covered with mutual shade, affecting the ventilation and light transmission. Excessive nitrogen in the fruit tree leaves the branches and leaves to grow, and they are unable to fully differentiate flower buds, and are prone to diseases and insect pests. In addition, fruit quality is poor, lack of sweetness, poor coloration, and ripening time is also late.
3) Types, properties and application of nitrogen fertilizers
There are many types of nitrogen fertilizers, which can be roughly divided into four types: ammonium, nitrate, amide and long-acting nitrogen fertilizers. The properties of various types of nitrogenous fertilizers, their transformation and application in soils have both their own features and their own characteristics.
4) Reasonable distribution and application of nitrogen fertilizer
(1) Reasonable distribution of nitrogen fertilizer
According to climatic conditions: Nitrogen fertilizer efficiency is affected by weather conditions such as rainfall, temperature, and light intensity. The nitrogen fertilizer efficiency in general dry areas and years is poor, and the wet areas and years have good fertilizer effects. Experiments showed that under drought conditions, fruit trees responded the least to the amount of nitrogen fertilizer, and the yield curve was flat. When the water supply was sufficient, the response to nitrogen fertilizer was the largest and the yield curve rose steeply. Therefore, especially in semi-arid and arid regions, this relationship of the effects of water on nitrogen effects has often become the basis for many countries to decide on the fertilization policy.
In northern China, the climate is characterized by dry and dry weather and poor soil moisture. During the growth of fruit trees, the problem of nitrogen leaching loss is not significant. Therefore, in the northern part of the distribution of nitrogen fertilizer, nitrate-nitrogen fertilizer is more suitable in the north. In the south, the climate is humid and the annual rainfall is large. The loss of nitrogen leaching and denitrification is a serious problem. Therefore, ammonium should be distributed in the south. At the time of application, nitrate nitrogen fertilizer is applied as much as possible in dry conditions, and ammonium nitrogen fertilizer is applied to paddy fields.
According to soil fertility conditions: In order to improve the nitrogen fertilizer efficiency, the allocation of nitrogen fertilizer should pay attention to fertilization in middle and low yield fields. At present, most places generally pay attention to the high-yield pastoral areas and neglect the middle and low-yield pastures. This does not enable the existing chemical fertilizers to maximize their economic benefits and achieve an equilibrium increase in production.
According to fruit tree species and species characteristics: Fruit trees are very sensitive to nitrogen fertilizers and require a well-balanced supply of nitrogen. Excessive nitrogen nutrition can easily make nutrients grow too much, affect the fruit setting rate, and cause a decline in yield and quality. Normal apple, pear, cherry and other pure nitrogen amount is 4-6 kg per mu. Sometimes even 8 kg, which is mainly based on soil fertility.
(2) Amount of nitrogen fertilizer application
Grasping the appropriate amount of nitrogen fertilizer is an important part of reasonable application of nitrogen fertilizer. The amount of nitrogen fertilizer required for optimal production depends largely on the type of fruit tree, soil fertility, climate, and agricultural technical conditions. Determine the nitrogen fertilizer application of a fruit tree should mainly be based on multi-year field trials. At present, there are also using a push algorithm to determine the amount of nitrogen fertilizer.
(3) Deep nitrogen fertilizer application
The deep application of ammonium nitrogen fertilizer and urea is an important measure to prevent nitrogen loss and improve nitrogen fertilizer efficiency. Deep application can reduce the direct volatilization of ammonia, reduce nitrification leaching and denitrification loss. The long-lasting fertilizing effect can overcome the shortcomings of the premature appetite and the premature aging of defertilization at the later stage. Deep application is conducive to promoting the development of the root system and enhancing the absorption of nutrients. The deep application methods include basic fertilizer deep application, dressing fertilizer ditch application, and acupoint application.
(4) Application of nitrogen fertilizer in combination with other fertilizers
The application of nitrogenous fertilizer and organic fertilizer: The application of nitrogenous fertilizer combined with organic fertilizer plays an important role in obtaining high yield, stable production, and reducing costs of fruit trees. It is also an important means to improve the soil and increase fertility.
The results of long-term experiments in various countries have shown that chemical fertilizers generally cannot increase soil organic matter or nitrogen levels, and in most cases cause a deficit in soil organic matter and nitrogen. Only applying organic fertilizer can increase soil organic matter and increase soil nitrogen content.
According to the study, organic fertilizers combined with chemical nitrogenous fertilizers changed the characteristics of nitrogen supply and the fate of nitrogen. In mixed application, inorganic nitrogen can increase the mineralization rate of organic nitrogen, and organic nitrogen can increase the biological assimilation rate of inorganic nitrogen. Therefore, in the organic and inorganic fertilizer application system, the nitrogen supply status of the soil obviously has higher and lasting fertilizer efficiency than the organic nitrogen application. Therefore, the combined application of organic manure and chemical nitrogen fertilizer is an important means to increase soil nitrogen fertility and ensure the sustained high yield and stable production of fruit trees.
Nitrogen fertilizer and organic fertilizer application: In recent years, the amount of nitrogen fertilizer increased rapidly, the northern phosphate fertilizer, the application of the corresponding shortage of potash fertilizer in the south, the nutrient supply is not balanced, therefore, significantly affects the exertion of nitrogen fertilizer efficiency. In northern China, soil-enriched parent materials are rich in potassium. Under current production conditions, attention should be paid to adjusting the proportion of nitrogen and phosphorus. The test results in various areas also showed that the effect of increasing nitrogen and phosphorus fertilizer application is often higher than that of single nitrogen fertilizer application. In the southern region, due to the high phosphorus application rate in the past 20 years, phosphorus has accumulated in the soil, and the potassium in the soil is often insufficient. Therefore, attention should be paid to adjusting the proportion of nitrogen and potassium or the proportion of nitrogen, phosphorus and potassium. The effect of combined application of nitrogen and potassium fertilizers or N, P and K fertilizers is often higher than that of single application of N fertilizers.
2, phosphorus
Phosphorus is one of the three elements of plant nutrition. Phosphorus content in the soil (referring to topsoil) fluctuates greatly, and many of China's soil phosphorus supply is insufficient. Therefore, the directional adjustment of phosphorus status and the rational application of phosphate fertilizer is one of the important measures to improve soil fertility and achieve high yield and quality of fruit trees.
1) The physiological function of phosphorus
(1) Phosphorus is a component of important compounds in plants. Phosphorus is an important constituent of nucleic acids.
(2) Phosphorus can enhance photosynthesis and carbohydrate synthesis and operation.
(3) Promote nitrogen metabolism.
(4) Improve the adaptability of fruit trees to the external environment. Phosphorus can improve the ability of fruit trees to resist drought, cold and disease.
2) Symptoms of Phosphorus Disorders
The symptoms of phosphorus deficiency were not as pronounced as the lack of nitrogen in morphological manifestations. In the absence of phosphorus, various metabolic processes are inhibited, plant growth is retarded, dwarf, thin, erect, roots undeveloped, and fruits are small.
Phosphorus-deficient plants have small leaves, dark green or grayish green leaves, and lack luster. This is mainly due to poor cell development, resulting in relatively high chlorophyll density. Phytophosphate deficiency in plants is beneficial to the absorption and utilization of iron and indirectly promotes chlorophyll. The synthesis makes the leaf color darker. When phosphorus deficiency is severe, carbohydrates in the plant are relatively accumulated and more anthocyanins are formed. Therefore, purple spots or stripes appear on the stem. In severe cases, the leaves come off. Symptoms generally begin with the old leaves of the base and gradually develop upward.
Excessive phosphorus can enhance the respiration of crops, consume large amounts of carbohydrates, leaves thick and dense, early development of reproductive organs, stem and leaf growth inhibition, causing premature aging. As water-soluble phosphates can produce low-solubility compounds with nutrients such as zinc, iron, and magnesium in the soil, the effectiveness of these elements is reduced. Therefore, a condition in which hard gas is caused by excessive phosphorus is often manifested in chlorosis such as zinc deficiency, iron deficiency, and magnesium deficiency.
According to extensive analysis of China's arable land, it is estimated that about one-third of cultivated land will lack phosphorus. The soil in the south is generally deficient in phosphorus, and there are many areas in the north that have obvious effects on increasing production.
3) Types and application of phosphate fertilizers
Phosphate fertilizer produced by various methods can be divided into three types according to the solubility of the phosphate contained therein, insoluble phosphate fertilizer, water-soluble phosphate fertilizer and weakly soluble phosphate fertilizer.
4) Reasonable distribution and application of phosphate fertilizer
The effective application of phosphate fertilizer should be comprehensively considered based on soil properties, characteristics of fruit trees, crop rotation systems, phosphate fertilizer varieties, and application techniques.
(1) The ratio of soil available nitrogen to available phosphorus is one of the important factors affecting phosphate fertilizer efficiency. In the condition that the soil is low in nitrogen and phosphorus, most of the application of phosphate fertilizer has a good effect of increasing production. The greater the ratio, the more obvious the effect of phosphate fertilizer.
There is a significant positive correlation between soil organic matter content and available phosphorus content. The higher the organic matter content, the higher the available phosphorus content of the soil.
Soil pH also affects the availability of phosphorus: For most soils, the availability of phosphorus is in the range of pH 5.5 to 7.9, which is lower than the pH 5.5 or above pH 7.0. Soil pH also affects the absorption of crop roots, which in turn affects phosphorus uptake.
Factors such as soil ripening degree and fertilization also affect the content of available phosphorus in the soil: For soils with high maturation and organic fertilizers, the available phosphorus is also higher, and the effect of applying phosphate fertilizer is poorer, whereas the fertilizer efficiency increases.
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