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1. Determine the amount of topdressing based on soil fertility
Practice has proved that increasing the amount of fertilizer applied to the middle and low-yield fields can significantly increase the yield. For high-yield fields, the general fertilization level can be maintained. Generally, on the basis of applying the fertilizer and fertilizer as the base fertilizer, taking the two crops of corn and sorghum as an example, on the high-fertility soil, 20 kg per mu is applied; in the medium-fertile soil, 23 kg per mu is applied; On low-yield soils, 27 kg should be applied.
2. Topdressing in the season of crop nutrition
The main role of top dressing is to use fertilizer to regulate the growth of crops, to meet the nutritional needs of crops in the middle and late stages of growth, and to achieve the purpose of increasing production. The key to improving the utilization rate of fertilizers is to grasp the critical period and maximum efficiency period of nutrient absorption of various crops, and try to improve the utilization rate of fertilizers in the nutrient period of crops. Corn should be in the period from jointing to big bell, sorghum should be from jointing to booting stage, rice from greening to tillering, and sunflower in the bud stage. During the three-leaf stage of wheat, soybeans are topdressed with urea at the early flowering stage.
3. Doing deep application
Practice has proved that after applying urea to the surface of the ground for 4-5 days at room temperature, most of the nitrogen will be ammonia volatilized, and its utilization rate is only about 30%, especially on the surface of calcareous and alkaline soils. The loss of volatilization is more serious. Therefore, when using urea to topdress the dry crops, it is best to apply the pits or trenches to a depth of 10 cm, so that the urea can be placed in the moist soil, which is beneficial to the conversion of urea, and is also beneficial to the ammonia fertilizer. Adsorption reduces the loss of volatilization. When using urea to topdress rice, the water layer should not exceed 3-5 cm.
4. Keep a certain distance from the crop
Because of its high nitrogen content, urea has a large nutrient concentration and is highly hygroscopic. Therefore, in topdressing, it is necessary to prevent urea from being applied to the roots of the crops, and it is also impossible to drop urea into the heart leaves of the crops so as not to burn the seedlings and affect the growth, and it must be kept at a certain distance from the crops.
5. Apply earlier than other nitrogen fertilizers
Because urea is a low molecular organic compound, it must be ammoniated after being applied to the soil, that is, it can be converted into a highly volatile ammonium carbonate under the action of urease secreted by the decomposing bacteria. absorb. Therefore, the application of urea to crop topdressing should be applied about 7 days earlier than other nitrogen fertilizers.
6. Avoid mixing with alkaline fertilizer
Urea is a neutral fertilizer. When topdressing, avoid mixing with alkaline fertilizer to prevent reducing fertilizer efficiency. If it is not possible to mix with alkaline fertilizer, it is also necessary to stagger the date of fertilization, usually 3-5 days. However, when urea is mixed with fertilizers such as potassium chloride, phosphate rock and superphosphate, the yield increase effect is remarkable.
7. It is not advisable to fill the water immediately after the application
After urea is applied to the soil, it cannot be adsorbed by the soil before it is decomposed and converted. If you fill the water immediately after chasing, it will cause a large loss of urea. Soil water shortage is serious, non-irrigation is not time, but also to do small water and dip irrigation, avoid flooding. When topdressing rice, the characteristics of urea with greater fluidity before conversion should be taken into consideration. After the application, it is not possible to immediately irrigate the water. Generally, it is better to pour a small water 3-5 days after the chase.
8. Root dressing
Urea has less damage to crop leaves, is soluble in water, has strong diffusibility, and is easily absorbed by leaves. It is not easy to cause separation of the walls after entering the leaves, so it is very suitable for top dressing. However, urea with a biuret content of not more than 2% should be used to prevent damage to the leaves. The concentration of urea top dressing varies depending on the crop species. The concentration of top dressing of gramineous crops is 1.5%-2%; the concentration of root dressing for dicotyledon is 1%, which blooms in crops. The concentration should be smaller. Generally, the amount of top dressing per urea is 0.5-1.5 kg. The spraying time is preferably carried out after 4 pm. At this time, the amount of transpiration is small, and the leaf pores are gradually opened. The diluted urea solution can be absorbed in one night, which greatly improves the utilization rate of urea.
Urea is currently the highest concentration of solid nitrogen fertilizer produced in China, and its aqueous solution is neutral. In addition to the base fertilizer used in crops, urea is mostly used for crop topdressing. So, how can we improve the topdressing effect of urea? The main points should be as follows:
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