Urea, also known as carbamide, is a white crystal, one of the simplest organic compounds, and also the nitrogen fertilizer with the highest nitrogen content.
As a neutral fertilizer, urea is suitable for a variety of soils and plants. It is easy to preserve, easy to use, and has little damage to the soil. It is a chemical nitrogen fertilizer that is currently used in large quantities. In industry, ammonia and carbon dioxide are used to synthesize urea under certain conditions.
The nitrogen content of urea is high, and the application rate should not be too large, so as not to cause unnecessary waste and “fertilization damage”.
In addition, farmers in many fruit-producing areas use a large amount of urea, resulting in dead trees, and the consequences are very serious.
Urea has high nitrogen content, obvious effect after application, and no side effects. It can be used as base fertilizer, top dressing, and root top dressing, and is deeply loved by farmers. However, if the application method is incorrect and the application period is not suitable, the utilization rate will decrease significantly, and the utilization rate is only 10% to 20% in severe cases. Growers have spent money and wasted time, but they have not received the desired effect, and may even cause “fertilizer damage” and endanger crops. Therefore, it is very necessary to apply urea correctly and scientifically.
Do not use urea
- Avoid mixing with ammonium bicarbonate
After urea is applied to the soil, it must be converted into ammonia before it can be absorbed by crops, and its conversion rate is much slower under alkaline conditions than under acidic conditions. After the ammonium bicarbonate was applied to the soil, it showed an alkaline reaction, and the pH value was 8.2-8.4. The mixed application of ammonium bicarbonate and urea in farmland will greatly slow down the conversion of urea into ammonia, which will easily cause the loss and volatilization loss of urea. Therefore, urea and ammonium bicarbonate should not be mixed or applied at the same time.
- Avoid surface application
Urea is applied on the surface, and it will take 4 to 5 days to be used at room temperature. Most nitrogen is easily volatilized in the process of ammonification, and the actual utilization rate is generally only about 30%. If it is in alkaline soil and organic matter content Nitrogen loss will be faster and more when applied in high soil. And shallow application of urea, easy to be consumed by weeds. Deep application of urea melts the fertilizer in the soil, making the fertilizer in the moist soil layer, which is conducive to the exertion of fertilizer efficiency. For topdressing, it should be applied in holes next to the seedlings or in a ditch on the side of the seedlings, and the depth should be about 10-15cm. In this way, urea is concentrated in the root-dense layer, which is convenient for crops to absorb and utilize. Tests have shown that deep application can increase the utilization rate of urea by 10% to 30% compared with shallow application.
- Bogey as seed fertilizer
During the production process of urea, a small amount of biuret is often produced. When the biuret content exceeds 2%, it will cause toxicity to seeds and seedlings. Such urea entering into seeds and seedlings will denature proteins and affect seed germination and Seedlings grow, so it is not suitable for seed fertilizer. If it must be used as seed fertilizer, avoid contact between seed and fertilizer, and control the amount.
- Immediately after the four bogey watering
Urea is an amide nitrogen fertilizer. It must be converted into ammonia nitrogen before it can be absorbed and utilized by crop roots. The conversion process varies depending on soil quality, water and temperature conditions. Generally, it takes 2 to 10 days to complete. Immediately after irrigation and drainage or dry land is applied before heavy rain, urea will be dissolved in water and lost. Generally, water should be watered 2 to 3 days after application in summer and autumn, and water should be watered 7 to 8 days after application in winter and spring.
- Bogey and alkaline fertilizer mixed application or simultaneous application
After urea is applied, it must be converted into ammonia nitrogen to produce fertilizer effect. Under alkaline conditions, most of the nitrogen will become ammonia and volatilize. Therefore, urea cannot be mixed with lime, plant ash, calcium magnesium phosphate fertilizers, etc. Fertilizers are mixed or applied at the same time. Generally speaking, in summer and autumn, urea and alkaline fertilizers should be applied 3 to 4 days apart, and 7 to 8 days in winter and spring.
- Taboos on celery
During the entire growth period of celery, a large amount of nitrogen fertilizer should be applied, but urea should not be applied. Because of topdressing urea, celery fiber increases and becomes thicker, the plant ages, the growth is slow, and the food has a bitter taste, and the quality is poor. Celery is suitable for applying ammonium bicarbonate, ammonia water and organic fertilizer, which is beneficial to improve the quality.
- Avoid excessive dosage
The nitrogen content of urea is high, and the application rate should not be too large, so as not to cause unnecessary waste and “fertilization damage”. Generally, 5-15 kg is applied per mu, and 15-20 kg per mu in paddy fields. If applied too much, it cannot be absorbed by the soil before it is converted into ammonium bicarbonate, and it is easy to be leached by rainwater, and it is easy to damage crops. At the same time, too much urea is applied, and most of it is lost and enters the groundwater, which will lead to nitrogen pollution in the water body, resulting in the deposition of nitrite, which will seriously affect the safety of humans and animals.
- Bogey high concentration foliar spraying
Among all nitrogen fertilizers, urea is the most ideal foliar fertilizer. Spraying urea, the quantity and speed of crop protein synthesis are more than other nitrogen fertilizers. However, when spraying on the leaves, avoid excessive concentration of urea solution, otherwise it will burn the leaves and poison the plants. Usually 2% is suitable for corn, wheat, rice and cotton; 0.5-1% for vegetables and fruits; 0.5-1.5% for fruit trees.
- Bogey application too late
Applying urea too late is not conducive to the exertion of fertilizer efficiency, and it is easy to cause crops to be greedy and late-maturing, so it should generally be applied 4 to 7 days earlier than other nitrogen fertilizers.
- Bogey single administration
The active ingredient of urea is nitrogen, which is a single nutrient, but the growth and development of crops requires a variety of nutrients. Therefore, urea should be applied in conjunction with organic fertilizers, phosphorus, and potassium fertilizers to meet the needs of crops for various nutrients. And the rational mixing of urea with organic fertilizer and chemical fertilizer can effectively improve its utilization rate. For example, the mixed application of urea and superphosphate can convert unstable ammonium bicarbonate into stable ammonium phosphate, so that the natural volatilization of nitrogen is greatly reduced. The mixed application of urea and organic fertilizers will produce organic acids during the fermentation process, which can also accelerate the transformation and decomposition of urea, be quickly absorbed by crops, and improve the utilization rate of urea.
How to use urea correctly
1 balanced fertilization
Urea is a pure nitrogen fertilizer, which does not contain phosphorus and potassium, which are essential elements for crop growth. Therefore, when topdressing, it should be based on soil testing and chemical tests, and use formula fertilization technology to apply nitrogen, phosphorus, and potassium fertilizers in a balanced manner. First, all the phosphorus and potassium fertilizers and some (about 30%) nitrogen fertilizers required for the whole growth period of the crops are combined with soil preparation and bottom application. Then apply about 70% of the remaining nitrogen fertilizer (urea can be used) as topdressing, of which about 60% are topdressing during the critical period of fertilizer demand and maximum efficiency period of crops, and about 10% are topdressing in the later stage. Only the reasonable combination and scientific application of nitrogen, phosphorus and potassium fertilizers can improve the utilization rate of topdressing urea.
2 Appropriate follow-up
Some unreasonable fertilization phenomena can often be seen in agricultural production: when the wheat turns green after spring every year, farmers take the opportunity of pouring green water to sprinkle or wash urea into the wheat field; Into the field; cabbage seedling stage with watering urea; tomato seedling watering urea and so on. Topdressing urea in this way, although the fertilizer is used, the waste phenomenon is serious (ammonia gas volatilizes, urea particles are lost with water), and it will also lead to excessive vegetative growth, late lodging of wheat and corn, tomato “blooming”, and delayed cabbage core and other adverse phenomena occur.
Each crop has a specific critical period for the absorption of nitrogen, phosphorus, and potassium (that is, the period when the crop is particularly sensitive to the absorption of certain elements). In this period, the lack of fertilizer (nitrogen, phosphorus, potassium) will reduce the yield and quality of crops, which will have a huge impact. Even if sufficient fertilizer is applied later, the impact on crop yield and quality will not be reversed. In addition, there is a period of maximum efficiency, that is, the fertilized crops in this period can obtain higher yields, and the crops have the highest utilization efficiency of fertilizers. From the above analysis, it can be seen that only when topdressing is applied during the nutritional critical period and maximum efficiency period of crops, can the utilization rate of fertilizer be improved and crops achieve high yield and high quality.
When urea is used as topdressing, it should be topdressed one week before the critical period of crop nitrogen demand and the period of maximum efficiency. Different crops have different critical period of fertilizer requirement and maximum efficiency period, so they should be treated differently and applied rationally. For example, wheat, corn and other gramineous crops have critical nitrogen requirements in the tillering stage and panicle differentiation stage, and cotton in the budding stage. Nitrogen maximum efficiency period: wheat is from jointing to booting stage, rice is from tillering to jointing stage, corn is in bell mouth stage, tomato is in fruiting stage, cabbage is in rosette stage, sunflower is in flower bud stage, soybean is in early flowering stage, etc.
3 Timely topdressing
Urea is an amide fertilizer, which needs to be converted into ammonium carbonate, absorbed by soil colloids, and then absorbed by crops. This process takes 6 to 7 days. During this period, urea is first dissolved by the water in the soil, and then slowly converted into ammonium carbonate. Therefore, urea When topdressing fertilizer is applied, it should be applied about 1 week before the critical period of crop nitrogen demand and the period of maximum fertilizer efficiency, and it should not be too early or too late.
4 Deep application of soil
Improper application methods can easily cause nitrogen loss such as urea loss with water, ammonia volatilization, waste of fertilizers, labor costs, and greatly reduce the utilization rate of urea.
The correct method of application is: apply on corn, wheat, tomato, cabbage and other crops, dig a hole 15-20 cm deep at a distance of 20 cm from the crops, apply the fertilizer and cover it tightly with soil, if the soil is not too dry In the case of watering after 7 days. When the soil is severely dry and watering is necessary, it should be watered lightly once with small water, and flood irrigation should not be used to prevent urea from being lost with water. When applying on rice, it should be applied by spreading, keep the soil moist after application, and do not irrigate within 7 days. After the fertilizer is fully dissolved and absorbed by the soil, it can be poured with a small amount of water, and then dried for 5-6 days.
5 foliar spray
Urea is easily soluble in water, has strong diffusivity, is easily absorbed by leaves, and has little damage to leaves. It is suitable for root topdressing and can be combined with crop pest control for foliar spraying. However, when topdressing the roots, urea with a biuret content of no more than 2% should be selected to prevent damage to the leaves. The concentration of root topdressing varies with different crops. The spraying time should be after 4 pm, when the transpiration is small and the stomata on the leaf surface gradually open, which is conducive to the full absorption of the urea aqueous solution by the crops.