First, determine the amount of top dressing based on soil fertility. Practice has shown that increasing the amount of fertilizer applied to the middle and low-yielding fields can significantly increase production. For high-yielding fields, the general level of fertilization can be maintained.
Second, top-dressing in the crop nutrition. The key to increasing the utilization rate of chemical fertilizers is to grasp the critical period and maximum efficiency period of nutrient absorption of various crops, and try to top-dress fertilizers during the nutrient-rich period of crops in order to increase the utilization rate of fertilizers.
Third, do deep cover. It has been proved that when urea is applied on the ground surface for 4 to 5 days at room temperature, most of the nitrogen will be volatilized, resulting in a utilization rate of only about 30%, especially on the surface of calcareous and alkaline soils. The loss is even more serious. Therefore, when urea is used to top-dress dry farm crops, it is better to grind the pits or deepen the ditch for less than 10 cm, so that the urea can be contained in the moist soil, which is conducive to the conversion of urea and is also conducive to the ammonia fertilizer. Adsorption reduces volatilization losses.
Fourth, to maintain a certain distance with the crop. Due to the high nitrogen content of urea and the high concentration of nutrients, it has great hygroscopicity. Therefore, when topdressing, it is necessary to prevent urea from being applied near the roots of crops, and it is even more important not to drop urea into the heart of the crop so as not to burn the seedlings and affect the growth. Therefore, it must be kept at a certain distance from the crop.
Fifth, early application. Because urea is a kind of low molecular organic compound, it must have an ammoniated process after being applied to the soil and be converted into a highly volatile ammonium carbonate before it can be absorbed by the crop roots. Therefore, using urea to topdress crops should be applied about 7 days earlier than other nitrogen fertilizers.
Sixth, do not mix with alkaline fertilizer. Urea is a neutral fertilizer and should not be mixed with alkaline fertilizers to prevent fertilizer efficiency. If non-mixed application with alkaline fertilizer is not possible, it is also necessary to stagger the fertilization date, usually every 3 to 5 days. However, when urea is mixed with potassium chloride, phosphate rock powder, and superphosphate, the effect of increasing production is significant.
7. Do not apply water immediately after topdressing. After urea is applied to the soil, it cannot be absorbed by the soil before it is converted and transformed. If you fill water immediately after chasing, it will cause a large loss of urea.
Soil water shortage, non-irrigation can not be time, but also to do small ground irrigation, avoid flooding irrigation. When topdressing rice, it should be considered that urea is more fluid before conversion, and it can't be immediately watered after topdressing. Generally, it is appropriate to fill small water once every 3 to 5 days after recovery.
Eight, it is advisable to do top dressing outside the roots. Urea has less damage to crop leaves, and is easily soluble in water. It is highly diffusive and easy to be absorbed by leaves. It is not easy to cause plasmolysis after entering the leaves, so it is suitable for top dressing. However, high quality urea with a biuret content of no more than 2% should be used to prevent damage to the leaves.
The concentration of urea as a topdressing fertilizer varies depending on the type of crops. The concentration of top dressings outside the crops is 1.5%~2%; the concentration of top dressings outside the double leaf crops is 1%, and the concentration during the flowering phase of the crop It should also be smaller. Generally, the amount of fertilizer applied outside the urea root per mu is 0.5 to 1.5 kg.
The spraying time is appropriate around 4:00 pm, when the evapotranspiration is small, the leaf pores gradually open, and the diluted urea solution can be absorbed completely at one night, which greatly improves the utilization of urea.
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