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 fattening effect of urea? The main points should be as follows:
　　 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. Maintain general fertilization for high-yield fields
Level can be. On the basis of general Shi foot base fertilizer agricultural fertilizer and chemical fertilizer on corn and sorghum crops, for example two, the high fertility of the soil, per acre topdressing 20 kg; 23 kg per acre topdressing medium fertility of the soil; On low-yield soils, 27 kg should be applied .
　　 2. Topdressing at the peak 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. Improve the utilization of fertilizer topdressing key is to master the critical period and the maximum efficiency of various crops on nutrient uptake, as far as possible in the peak crop fertilizer nutrients, in order to improve fertilizer utilization. Corn should be in the period from jointing to big bell; sorghum should be from jointing to booting; rice from greening to tillering; sunflower in the bud stage; wheat in the three-leaf stage; soybean in the early flowering stage.
　　 3. Do deep application of soil. Practice has proved that the urea is applied on the ground surface 4 to 5 days at room temperature, most of the nitrogen will evaporate amides which utilization rate is only about 30%, in particular lime and alkaline soil surface in which ammonia The volatile loss is more serious. Therefore, when the urea plant to a dry fertilizer, preferably planing open pit or groove depth 10 cm or less is applied, in this way to make the urea in moist soil, in favor conversion of urea, ammonia is also conducive to the soil fertilizer state Adsorption reduces the loss of volatilization. When using urea to topdress rice, the deepest water layer should not exceed 3 to 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 vicinity of the crop line, and it is not possible to drop urea into the heart of the crop to avoid burning the seedlings and affecting the growth. It must be kept at a certain distance from the crop.
　　 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 and converted into a highly volatile ammonium carbonate before it can be absorbed by the roots of the crop. Therefore, the application of urea to crop topdressing should be applied about 7 days earlier than other nitrogen fertilizers .
　　 6. Do not mix with alkaline fertilizer. Urea is a neutral fertilizer. When topdressing, avoid mixing with alkaline fertilizer to prevent reducing fertilizer efficiency. If administered mixed with a non-alkaline fertilizer is not available, but also the date of fertilization offset, generally separated 3--5 days to. 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 available, we must aim for small water ground irrigation, avoid flood irrigation. When dressing to paddy rice, consideration should be given to the urea greater mobility characteristics before conversion, not immediately after topdressing more irrigation, usually after 3 to 5 days to recover a small water irrigation is appropriate.
　　 8. Do root dressing. Urea smaller on leaf damage, but soluble in water, diffusion is strong, the blade easily absorbed into the blade easily cause plasmolysis, so it is suitable for foliar application. However, urea with a biuret content of not more than 2% should be used to prevent loss of the blade. Foliar concentration of urea do vary but are different types of crops, root crops of Gramineae outer dressing a concentration of 1.5% to 2%; double-leaf crops for foliar concentration of 1% concentration in crop flowering It 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 transpiration amount is small, the leaf surface pores are gradually opened, and the diluted urea solution can be basically absorbed overnight, thereby greatly improving the utilization rate of urea.
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