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 for top-dressing fertilizer application is not high, and it is not as good as the amount of ammonium, ammonium chloride and ammonium bicarbonate. Why? Please answer experts one by one below.
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 needs of the stage of high-yield crops, a certain amount of available nitrogen fertilizer or nitrogen-potassium compound fertilizer must be added. Since the root absorption efficiency is high at this time, as long as the amount and method of topdressing are used correctly, the utilization rate of nitrogen fertilizer will be very high, reaching 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, when the north early spring season of winter wheat turning green fertilizer, ground temperature about 10 ℃, the urea is converted into ammonium nitrogen takes about 7 to 10 days; local temperature rise 20 ℃, flare of dressing maize, cotton dressing squaring 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 ahead, it is necessary to adjust measures to local conditions. It is also the season of spring and summer. It takes a few days for the soil temperature to rise slowly in the northeast, and the soil temperature in the south of China is high, and the application of urea can be advanced by 1~2 days in advance. For the same area, because the paddy field temperature is slightly lower than the dry land, it should be treated differently.
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.
In short, urea as a top dressing application techniques: one to be applied in advance, the second to cover the soil.
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