Principle of application of pelleted urea in southern rice fields

Urea accounts for about 65% of China's nitrogen fertilizer production and application. How to use it directly is directly related to the output of agricultural products and environmental quality. Here, the application technology and effect of pelletized urea in southern rice fields are introduced.

The particle size of urea products at home and abroad can be generally divided into three grades: the size of conventional small urea is about 1.5 mm; the particle size of large granular urea is generally in the range of 2.00 to 4.75 mm, and the urea of ​​pellet (Fig. 1) is larger. The particles are larger and have a diameter of 5 or more. It is estimated that the actual production and sales volume of large granular urea in China is about 3 million tons. In the water and dry crop production system, there are not many direct application of large granular urea, mainly because the recognition is not in place. In fact, the difference in the size of the urea particle size changes the physicochemical properties and suitable properties of the two. For example, small particle urea has low strength, is easily broken during storage and application, and has a high volatilization rate on the soil surface. The large granular urea has high strength, is not easy to be broken and agglomerated, and is suitable for mechanized fertilization; it dissolves slowly in the soil, and has less volatile loss; the biuret content in the product is relatively low. In the fertilization method, small particles are suitable for top dressing, and large particles are suitable for base fertilizer.

In 2011, the Asian State Plant Nutrition Management Association launched a large-granule urea pellet granulation technology for the problems caused by the traditional use of a large amount of urea. The main technique is to apply large-grain urea of ​​more than 7 mm to 7 cm in the middle of 4-point rice by hand or mechanically during rice transplanting (Fig. 2). The results show that large granular urea is the base fertilizer of rice, and its deep application has significant agricultural and economic advantages. In terms of improving nitrogen use efficiency, the nitrogen utilization rate of ordinary urea (particle size 1.5 mm) is only about 32%. In the rice with large granular urea pellet granulation technology, the nitrogen fertilizer utilization rate can be as high as 65%. The International Fertilizer Development Center considers a large number of field trials of tropical and subtropical rice:

The deep application of large granular urea not only reduces ammonia volatilization loss, but also reduces greenhouse gas N2O emissions. Therefore, large granular urea plays a role in controlling agricultural non-point source pollution.

It is well known that the effectiveness of a fertilizer depends on whether the method of application is scientific and reasonable. Similarly, the emphasis on the fertilization method is to give full play to the advantages of the fertilizer variety itself, and to overcome its disadvantages.

At present, the recognition of large granular urea in China is not comprehensive enough and profound, so it is only applied to the nitrogen fertilizer raw material for the production of blended fertilizer (BB fertilizer). From the perspective of development, the role of large-grain urea in crop yield, nutrient efficiency and control of agricultural non-point source pollution requires the attention of China's domestic production and promotion departments.

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