How to properly administer urea，What is the harm of improper application of citrus urea?

1. The harm of improper application of urea to citrus

Urea is a neutral nitrogen fertilizer. High-quality urea (containing less than 0.5% biuret) has less harmful residues in the soil and can be used in citrus production. It is worth noting that as a fruit tree that is sensitive to urea, citrus is prone to root burning and poisoning when urea is applied improperly.

If the application amount of urea is too large or the spraying concentration is too high, the ammonium ions and ammonia accumulated by the urea into the citrus body for regeneration and hydrolysis will also increase. In the event of drought and high temperature, a large amount of ammonium ions will be converted into ammonia, causing the ammonia concentration to be too high. Toxic to citrus. Ammonia is a neutral molecule and has no charge. It can easily penetrate into roots through root cells and be transported to the above-ground part under the action of leaf transpiration. Not only does it damage the root system, but the above-ground parts are also severely affected. In addition, excessive application of urea will accumulate a considerable amount of nitrite ions around the fertilization area to poison the root system, especially under low temperature conditions, the accumulation is more.

Urea is sprayed on the ground, and it takes 4 to 5 days to transform at room temperature before it can be used. Most of the nitrogen is easily volatilized during the ammonification process. This will not only waste fertilizer, but also cause citrus roots to float up and burn the roots. root.

Biuret is a substance produced by urea molecules in a high-temperature chemical reaction. If urea is used continuously for a long time, it is easy to cause biuret poisoning. Citrus is very sensitive to biuret, and the accumulation of more than 0.25% will produce yellowing and brittle leaf tips and mosaic phenomena, reducing photosynthesis, causing premature leaf aging and shedding, affecting flowering and fruiting.

After the urea is dissolved, isomerization may occur to form ammonium cyanate; at the same time, ammonium carbamate is also formed during the hydrolysis process, and these substances are toxic to citrus.

Understanding the fertilizer requirements of fruit trees is a prerequisite for scientific fertilization. Topdressing in an appropriate period can achieve the desired effect. If the application period is not correct, it will not only waste fertilizer, but even affect the normality of plants.

For example, citrus flower bud differentiation requires nitrogen, phosphorus, potassium and other nutrient elements, but too much nitrogen will inhibit flower bud differentiation. In particular, a large amount of urea will cause the plant to grow too vigorously, and the vegetative growth and reproductive growth will lose balance, which will hinder the flower bud differentiation.

During the fruit setting period after the flowers fall, it is necessary to coordinate the contradiction between the fruit setting and the summer shoots. At this time, if urea is applied, it will stimulate the summer shoots to burst and cause a lot of fruit fall.

During the fruit coloring period, attention should be paid to the supplementation of phosphorus and potassium. Foliar sprays of phosphorus and potassium source pools can promote uniform and rapid color change. If urea with high nitrogen content is applied, it will affect the rate of color change, and at the same time, it is easy to produce puffy fruit.

2. Key points of applying urea to citrus

1. Use according to soil texture: Urea should be applied to clay soil. This type of soil usually has the characteristics of easy accumulation of organic matter, large amount of cation substitution, and good adsorption performance. The ammonia nitrogen generated after the decomposition of urea can be adsorbed or exchanged by the soil in time, thereby reducing the concentration of urea and its decomposed ammonium in the soil solution. If it is sandy soil, it is recommended to use other nitrogen fertilizer or use it at intervals.

2. Pay attention to the application method: the main points should be changed to acupoint application, concentrated application is ring furrow application, and the fertilization area should be expanded. Change the direct covering soil to mix well with soil and fertilizer, change the application in autumn and winter to uniform application in spring and summer, change the dry application to after rain or water application, and change the shallow application to deep application. Prevent direct contact between urea and citrus roots to reduce poisoning and improve fertilizer efficiency.

3. Pay attention to the application rate (or concentration): the amount of urea applied in the orange orchard should be determined by the age of the tree. Generally, the amount of urea per plant should not exceed 0.5 catties per plant in young orchards, and 15-20 catties per mu is appropriate; each plant in adult orchards No more than 1 catty, about 30 catties per mu is appropriate. When spraying on foliage, the concentration should be controlled at 0.2% to avoid spraying urea in the hot season.

4. Pay attention to the use of it: Urea is a pure nitrogen fertilizer, which does not contain phosphorus, potassium and other middle and trace elements in the macro elements necessary for crop growth, so it needs to be used in conjunction to promote nutritional balance.