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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 low- and medium-yield fields can significantly increase production. For the high-yield field plots, the current fertilization level can be maintained. Generally, based on the application of farmyard manure and chemical fertilizer as the base fertilizer, taking corn and sorghum as two examples, on high-fertility soil, 300 kg of urea should be applied per hectare (1 hectare = 15 mu); On the soil, 350 kg should be applied; in low-yield soil, 400 kg should be applied.
2, topdressing in the crop nutrition period. 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. The corn should be in the jointing period to the big bell mouth, the sorghum should be in the jointing to booting stage, the rice should be from the greening to the tillering stage, the sunflower should be in the bud stage, the wheat should be in the three-leaf stage, and the soybean should be applied in the early flowering stage.
3, to do deep application of soil. Practice has proved that urea is applied to the surface of the ground. After 4-5 days at room temperature, most of the nitrogen is ammoniated and volatilized, and its utilization rate is only about 30%, especially on the surface of calcareous and alkaline soils. The loss of ammonia 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 deepest water layer should not exceed 3-5 cm.
4. Keep a certain distance from the crop. Because urea has high nitrogen content and strong nutrients, it has great hygroscopicity. Therefore, when topdressing, it is necessary to prevent urea from being applied to the roots of crops, and it is also impossible to drop urea into the heart leaves of crops to avoid burning seedlings and affecting growth. Be sure to keep 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, 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, should not be mixed with alkaline fertilizer. Urea is a neutral fertilizer. Therefore, when using urea to crop the crop, it should not be mixed with alkaline fertilizer to prevent the fertilizer from being reduced. 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 it is filled immediately after the chasing, it will cause a large loss of urea. If the soil is seriously dehydrated, and non-irrigation is not possible, it is necessary to do a small water irrigation, and avoid flooding. When topdressing rice, it should take into account the characteristics of urea in the soil before conversion, and it is not possible to fill the water immediately after the application. Generally, it is better to fill the small water 3-5 days after the chase.
8, urea can be used as a root dressing. Because urea is a neutral fertilizer, it has less damage to crop leaves, and is easily soluble in water. It is very diffuse and easily absorbed by crop leaves. After urea enters the leaves, it is not easy to cause separation of the walls. Nitrogen fertilizer is very suitable for root dressing of crops. However, urea with a biuret content of not more than 2% should be used to prevent damage to the leaves. The concentration of urea as top dressing varies depending on the crop species. The concentration of top dressing of gramineous crops is 1.5-2%; the concentration of top dressing for dicotyledon is 1%, when applied during flowering of crops The concentration should also be smaller. Generally, the amount of top dressing with urea root per hectare is 7.5-22.5 kg. The spraying time should be carried out after 4 pm, because the amount of air transpiration is small, and the leaf stomata are gradually opened, and the leaves can basically absorb the diluted urea solution in one night, greatly improving the urea. Utilization rate.
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