When corn and cotton are topdressing, farmers' friends always like to use urea, thinking it's going to get faster. However, a large number of field fertilizer efficiency surveys have shown that the utilization rate of nitrogen in top-season fertilizer application is not high, and it is not as good as nitrogen, such as thiamin, ammonium chloride and ammonium bicarbonate. Why? First of all, we must understand the purpose of applying fertilizer to crops and the requirements for fertilizers. Fertilizing is a period of rapid growth of crops, which is generally a period of large-scale growth of both vegetative and reproductive organs. It is the period in which crops require the most nutrients. In order to meet the stage requirements for high-yield crops, it is necessary to add a certain amount of quick-acting nitrogen fertilizer or nitrogen-potassium compound fertilizer. Since the root absorption efficiency is high at this time, as long as the amount and method of top dressing are used correctly, the utilization rate of nitrogen fertilizer will be very high, which can reach 50-70%. For the purposes and requirements of topdressing, fertilizer varieties must have the characteristics of easy dissolution, absorption and rapid fertilizer efficiency. Urea is often used by farmers as the preferred nitrogen fertilizer for topdressing, and it is generally believed that it has a high nitrogen content and is quick-acting. The actual fertilizer supply characteristics of urea: At present, most people directly engaged in agricultural production, for the understanding of the "quick effect" of urea, are often not comprehensive enough. Actually, urea is an organic small molecule nitrogenous fertilizer that is applied to the surface of Soon dissolved, but the molecular roots of urea crops have not been able to absorb and use it directly and in large quantities. The decomposition of urease must be carried out. After urea is converted into ammonium nitrogen, it can be rapidly and massively absorbed and utilized by crop roots. This shows that the effect of using ammonium sulfate, ammonium chloride and ammonium bicarbonate as top-dressing is definitely faster than that of urea. They can be absorbed and utilized without conversion, and they are more in line with the purpose and role of top-dressing. How long does it take for urea to complete its conversion? What factors influence the conversion rate? This determines that urea for top dressing is a few days earlier than other ammonium nitrogen fertilizers. Scientific experiments show that the urea conversion process is affected by various factors such as soil temperature, moisture content, organic matter content, pH, etc. In general farmland, when soil moisture and pH are basically suitable for normal growth of crops, the soil temperature is the rate of urea conversion. the main factor of influence. For example, in the early spring when winter wheat is applied to the green season, the ground temperature is about 10°C, and it takes about 7-10 days for the conversion of urea nitrogen to ammonium nitrogen; when the local temperature rises to 20°C, the spring corn is used as the top dressing during the bell stage, and the cotton is cultivated during the budding stage. When wheat and wheat are used in the booting stage, the conversion of urea to ammonium nitrogen takes about 5 days, but it takes only 3 days after the local temperature rises to 25°C. Therefore, the use of urea fertilizer is better than other ammonium nitrogen fertilizers for several days in advance. As for the specific days in advance, it is necessary to adjust to local conditions. When urea is used as topdressing in summer, it is also necessary to pay attention to timely soiling or irrigation. Due to the high temperature, urea conversion is fast, and the product after urea conversion is ammonium carbonate, which is less than the nature of ammonium bicarbonate, commonly known as “gas-fetal fertilizerâ€. Stable, it will produce large amounts of ammonia. If you do not bury urea in the soil or sprinkle it on the ground without immediate watering, then the consequences of volatilization of ammonia will cause the leaves to burn. In severe cases, the leaves of the plant will be boiled, even if the ammonia is not roasted. The loss of nitrogen caused by the leaves will also pollute the environment and reduce the utilization rate. 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