How to use urea has a good effect?

How to use urea has a good effect? What should be paid attention to in the application of urea? Also ask the netizens who know to help introduce that urea is a kind of high concentration nitrogen fertilizer, which is a neutral quick-acting fertilizer, and can also be used to produce a variety of compound fertilizers. Urea does not leave any harmful substances in the soil, and there is no adverse effect of long-term application. The correct use of urea can make the fertilizer effect more lasting. The farming network has sorted out the application method of urea, which is listed in detail below for netizens' reference. First, determine the amount of topdressing according to soil fertility: practice has proved that increasing the amount of fertilizer applied to low-and medium-yield fields can significantly increase the yield. For the high-yield fields, the general fertilization level can be maintained. Generally, on the basis of fully applying agricultural fertilizer and chemical fertilizer as base fertilizer, taking corn and sorghum as an example, 20 kg per mu is applied in high fertility soil, 23 kg per mu in medium fertility soil, and 27 kg per mu in low yield soil. Application method 2, used as topdressing in the peak period of crop nutrition: the main function of topdressing is to use fertilizer to adjust the growth and appearance of crops, to meet the nutritional needs of crops in the middle and later stages of growth, and to achieve the purpose of increasing yield. The key to improve the utilization rate of topdressing chemical fertilizer is to grasp the critical period and maximum efficiency period of nutrient absorption by various crops, and to topdressing in the peak period of crop nutrition as far as possible in order to improve the utilization rate of fertilizer. Corn should be in jointing to big trumpet stage; sorghum should be in jointing to booting stage; rice from turning green to tillering stage; sunflower in budding stage; wheat in three-leaf stage; soybean topdressing urea in early flowering stage. Application method 3. Deep application of covering soil: through experiments, after applying urea to the ground surface at room temperature for 4-5 days, most of the nitrogen will be ammoniated and volatilized, and its utilization rate is only about 30%, especially on the surface of calcareous and alkaline soil. the loss of ammonia volatilization is more serious. Therefore, when topdressing upland crops with urea, it is best to apply less than 10 cm deep in pits or trenches, so that urea can be placed in wet soil, which is beneficial to the transformation of urea, and is also beneficial to the adsorption of ammonia fertilizer by the soil and reduce volatilization loss. When topdressing rice with urea, the depth of the water layer should not exceed 3-5 cm. Application method 4. Keep a certain distance from the root of the crop: urea has great hygroscopicity because of its high nitrogen content and high nutrient concentration. Therefore, when topdressing, it is necessary to prevent urea from being applied near the polar system of crops, not to mention dropping urea into the heart leaves of crops, so as not to burn seedlings and affect growth, and be sure to keep a certain distance from crops. Application method 5. Apply urea in advance: because urea is a low molecular weight organic compound, there must be an ammoniation process after being applied to the soil and transformed into a highly volatile ammonium carbonate before it can be absorbed by crop roots. Therefore, topdressing crops with urea should be applied about 7 days earlier than other nitrogen fertilizers. Application method 6, do not mix with alkaline fertilizer: urea is a neutral fertilizer, topdressing must not be mixed with alkaline fertilizer at the same time, in order to prevent the reduction of fertilizer efficiency. If it must be mixed with alkaline fertilizer, the date of fertilization should be staggered, usually every 5 days. However, when urea is mixed with potassium chloride, phosphate rock powder and calcium superphosphate, the yield increase effect is very significant. Application method 7. After urea is applied, it can not be irrigated immediately: after urea is applied into the soil, it cannot be absorbed by the soil before it is decomposed and transformed. If you irrigate immediately after the chase, it will cause a large amount of urea loss. When the soil is seriously short of water and must be irrigated, small water should be irrigated frequently, and flood irrigation must be avoided. When topdressing rice, the fluidity of urea before transformation should be taken into account, and it is more difficult to irrigate immediately after topdressing. Generally, it is appropriate to irrigate once every 3-5 days after topdressing. Application method 8, used as extra-root topdressing (foliar spraying): urea has less damage to crop leaves, is easy to dissolve in water, has strong diffusivity, is easy to be absorbed by leaves, and is not easy to cause plasmalemma separation after entering leaves, so it is very suitable for extra-root topdressing. However, urea with biuret content not more than 2% should be selected to prevent the loss of leaves. The concentration of urea for extra-root topdressing varies with different crop types, such as 1.5%-2% for Gramineae crops, 1% for double-leaf crops, and less at flowering stage. Generally, the amount of topdressing outside the root of urea per mu is 0.5-1.5 kg. The suitable spraying time is after 4: 00 p. M., when the transpiration is less, the leaf stomata open gradually, and the diluted urea solution can be absorbed overnight, which greatly improves the utilization rate of urea. What are the common nitrogen fertilizers? what are the large granulated urea?