If the seedlings are badly burned, the plants will die. Therefore, in the actual crop cultivation management, we need to treat and deal with them correctly. It must be noted that seedling burning is caused by improper fertilization, not only chemical fertilizer, but also organic fertilizer, especially the compost made of livestock urine is not decomposed.
Figure 1: Fertilizing crops
First, the symptoms of fertilizer burning seedlings
Because many farmers easily confuse fat seedlings with diseases, element deficiency disease's disease and pesticide hazards after burning, they need to judge and distinguish them correctly. In the actual crop cultivation process, fat seedling burning can be divided into the following four types according to the occurrence position and symptoms.
1, dehydrated and burned seedlings
The symptom of dehydrated fertilizer seedling burning is that after a few days of fertilization, the leaves above the ground wither like frost and gradually dry up (Figure 2). The main reason is that the amount of available water-soluble fertilizer is too much, and the fertilization position is too close to the root. After fertilization, the soil is too dry and easy to occur, and in severe cases, all plants dry up and die.
The symptoms of seedling burning of dehydrated fertilizer seedlings are very similar to those of soil drying and low physiological function of roots caused by long-term watering of cultivated land. The key point of identification is whether there is a lot of fertilization in the past few days, whether all cultivated land or only some plants have dehydration symptoms. If there are a lot of records of fertilization in the past few days and only some plants have dehydration symptoms, it can be roughly determined that it is fertilizer burning seedlings.
Fig. 2: excessive fertilization causes symptoms of dehydration and seedling burning of grapes.
Step 2 burn leaves and seedlings
The symptom of fat seedling burning leaf type is that the leaves turn pale yellow from the edge, and then gradually turn white or yellow. The range of discoloration is limited to the leaf margin, and basically does not extend to the whole leaf surface. Discolored leaves will not return to their original state, and will eventually dry up and fall leaves with the aging of leaves (Figure 3). Burning leaf fertilizer and seedlings mostly occurs when the fertilizer type is wrong or the concentration of foliar fertilizer is too high, or in greenhouse cultivation, plastic film cultivation and greenhouse cultivation where a large number of immature compost of livestock manure is used as base fertilizer.
The symptoms of leaf-burning fertilizer seedlings are similar to some nutrient deficiency symptoms, but the symptoms of leaf-burning fertilizer seedlings mostly occur in the hot season with strong sunshine, after applying high-concentration nitrogen fertilizer on the leaves or applying a lot of immature organic compost as base fertilizer. This phenomenon is concentrated on seedlings and young leaves, and the harm scope expands rapidly after it appears, mostly extending to the whole cultivation field.
Fig. 3: Cucumber leaf burn caused by ammonia poisoning.
Step 3 burn roots and seedlings
Root-burning symptoms of fertilizer seedlings refer to the phenomenon that crop roots, especially young roots, turn brown and die after fertilization (Figure 4). If not treated correctly in time, the symptoms may spread to the whole root system, leading to plant death. This symptom mainly occurs in the case of one-time over-fertilization of quick-acting fertilizer, application of a large number of immature organic fertilizers and direct contact with roots in a small area.
The symptoms of burning roots often appear at the same time as the symptoms of burning seedlings with dehydrated fertilizer on the ground. The symptoms of burning root fertilizer and seedlings may be confused with the phytotoxicity caused by some herbicides, which can be judged according to the records of whether herbicides are used or not.
Fig. 4: Symptoms of grape root burning caused by excessive fertilization.
4. Prevent sprouting and burning seedlings
The symptoms of seedling burning of fertilizer with germination obstacle are that the germination rate of seeds is very low after sowing, and the young roots germinated by seeds are dehydrated and dry, which leads to failure to germinate or abnormal buds and leaves cannot stretch (Figure 5). In the soil where lime nitrogen (calcium oxide cyanide) has been applied before sowing, it is easy to appear this symptom when mixing inferior calcium superphosphate with immature organic fertilizer as seed fertilizer or applying excessive urea as seed fertilizer to make seeds directly contact with fertilizer.
Fig. 5: Corn germination obstacle caused by direct contact between seeds and seed fertilizer.
Second, the reasons for burning seedlings with chemical fertilizers
There are three main reasons for crop fertilizer to burn seedlings:
1. The high concentration of fertilizer in soil affects the absorption function of roots.
Plants need to constantly absorb water and nutrients during normal growth and development. The absorption of water by root system depends on the osmotic pressure caused by the difference of solute concentration in the solution inside and outside the root cell. Simply put, plant root cell membrane is a semi-permeable membrane. Under normal circumstances, the concentration of ions and organic acids in root cells is higher than that in soil solution outside the root, which keeps the root cells at a low water potential and produces osmotic pressure between the root and soil solution.
The water in the soil solution enters the root cells through the cell membrane under the osmotic pressure, and then is sent to the aboveground part for supply to the stems and leaves. However, if one-time fertilization is excessive, especially if the fertilizer with high water solubility is applied too much, the concentration of fertilizer components in soil solution will increase rapidly. If the solute concentration in the soil solution exceeds that in the root cells, the osmotic pressure of the soil solution will be higher than that of the root cells, and the root cells will not only be unable to absorb water, but also the water in the cells will flow out into the soil (Figure 6). In this way, not only can not absorb water for the stems and leaves of the above-ground parts, but also the physiological functions of the roots will be damaged. If it lasts for a long time, the roots will dehydrate and die. This is the main cause of fat seedling burning, and its symptoms are dehydration type, partial root burning type and germination obstacle type.
Fig. 6: Relationship between osmotic pressure and water movement between soil solution and root cells.
2. Ammonia gas produced by fertilizer will do harm to leaves.
After applying ammonium sulfate, urea and other nitrogen fertilizers and organic fertilizers with livestock manure as the main component, ammonia contained in these fertilizers or ammonia produced by ammoniation of soil microorganisms will vaporize and volatilize under the weather conditions of high temperature and strong sunshine. In greenhouse cultivation and film mulching cultivation, due to the closed production environment and poor ventilation, ammonia volatilized from the soil stays in the closed space, and high concentration ammonia invades the leaves from the stomata of the leaves to destroy chlorophyll, which makes the leaves whiten (Figure 2). Most of the seedlings burned with leaf fertilizer are caused by this reason.
In addition, due to greenhouse cultivation and plastic film mulching cultivation, soil temperature will rise and soil evaporation water will increase. Water vapor is blocked by the covered plastic film and cannot be emitted into the atmosphere, but adheres to the plastic film and blades to form condensed water. These condensed water contains harmful substances such as ammonia, which will destroy the leaf tissue and form white or yellowish brown spots after contacting with the leaves (Figure 7).
It must be noted that the yellow-brown spots on crop leaves in greenhouse and greenhouse cultivation in winter are not necessarily caused by ammonia gas in fertilizer, but also by sulfurous acid gas generated when burning heavy oil or natural gas for heating, which needs to be distinguished from burning seedlings with fertilizer.
Fig. 7: Spots on Chinese cabbage leaves caused by condensed water in plastic film greenhouse.
3. Damage to crops caused by harmful components or decomposition products contained in fertilizers.
Lime nitrogen (calcium cyanamide) is a kind of nitrogen fertilizer. After application, cyanamide produced by decomposition in water is a powerful herbicide and insecticide/bactericide. If it is not used properly, the residual melamine in the soil will kill seeds and seedlings, leading to seedling shortage and broken ridges. Biuret contained in urea will hinder crop germination and new leaf spreading. If it is used for foliar spraying, it will hinder leaf spreading and induce albinism (Figure 8). Calcium superphosphate contains strongly acidic free acids. When organic fertilizer is decomposed and decomposed, it will produce a lot of heat and organic acids. If it comes into contact with the roots, it will cause dehydration and death of the roots. If these fertilizers containing harmful components or decomposition products are used as base fertilizer, seed fertilizer during sowing and root fertilizer during transplanting, it will become the cause of burning roots and preventing sprouting fertilizer from burning seedlings.
Fig. 8: biuret combustion caused by urea diffusion on mulberry leaves.
In some cases, it may be the burning symptoms of fat seedlings caused by the above reasons, which need to be judged separately.
Three, the prevention and emergency measures of fertilizer seedling burning
1, preventive measures for burning seedlings with chemical fertilizer
The preventive measures for fat seedling burning are simple. As long as you pay attention to the following matters when applying fertilizer, you can effectively prevent the burning of fat seedlings.
Excessive fertilization: In particular, it is necessary to avoid applying a large amount of fertilizers with high nitrogen content and good water solubility at one time. Don't use immature organic fertilizer: Never use immature organic fertilizer, especially immature compost mainly composed of livestock manure and urine. Pay attention to the location of fertilization: especially when applying base fertilizer and seed fertilizer, direct contact between fertilizer and seeds or seedlings should be avoided. Pay attention to foliar spraying: When foliar spraying, the solution must be prepared in strict accordance with the prescribed concentration, and the spraying precautions must be strictly observed. Do not use urea with excessive biuret for foliar spraying. Pay attention to the combination of fertilization and watering: after direct application of ammonium chloride, potassium chloride or compound fertilizer containing a large amount of ammonium chloride, irrigation must be carried out in a timely and appropriate amount to wash away excess chloride ions. Pay attention to ventilation: both greenhouse cultivation and plastic film mulching cultivation need proper ventilation. Especially in the period of strong sunshine and high ground temperature, the number of air changes should be increased appropriately. 2. Emergency measures for burning seedlings with fertilizer
If the symptoms of burning fat seedlings are found, corresponding measures should be taken as soon as possible to minimize the harm and reduce the loss. The following emergency measures can usually be taken.
After fertilization, when it is found that some leaves on the ground are dehydrated and germinated, irrigation should be carried out immediately to reduce the concentration of fertilizer components in soil solution. If possible, plow between ridges and scatter fertilizer into the soil as much as possible. When burning leaves are found in closed cultivation facilities, increase the number of air changes. If possible, carry out intertillage, dig out the topsoil and release the accumulated ammonia in the soil. After controlling the spread of fertilizer seedling burning symptoms, urea and potassium dihydrogen phosphate solution can be sprayed on leaves to help weak roots repair water and nutrient absorption functions and promote crop recovery. When there are serious obstacles to germination and seedling growth, give up quickly, replant or replant, or replant other crops to reduce losses. Figure 9: Healthy cucumber.
In the actual cultivation of crops, reasonable fertilization measures should be taken first to avoid the phenomenon of fertilizer burning seedlings; Secondly, if fertilizer seedlings are accidentally burned, the best emergency measures should be sought according to the reasons for burning seedlings. Through the combination of prevention and emergency treatment, it can effectively prevent fertilizer from burning seedlings or minimize the loss after burning seedlings.