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The urea formula is CO(NH2)2, which contains 46% nitrogen (N) and is white or pale yellow. It is easily soluble in water, the aqueous solution is neutral, and the hygroscopicity is strong. Because of the addition of hydrophobic substances such as paraffin in the production of urea, its hygroscopicity is greatly reduced.
The nature of urea should be emphasized: 1 Urea contains a small amount of biuret, also known as biuret. When it exceeds 1%, it has obvious inhibitory effect on crop growth. It is not suitable for seed fertilizer, seedling fertilizer, foliar fertilizer or excessive use. concentrated. 2 Urea is an organic nitrogen fertilizer, which is easily absorbed by crops after being converted into urease or ammonium bicarbonate by the conversion of urease in the soil. It is generally applied 4 to 8 days in advance. 3 Urea is molecular state before conversion, not adsorbed by soil, should be prevented from water loss; ammonia after conversion is also volatile, deep soil application.
2, application technology Urea can be used as base fertilizer and top dressing, generally do not directly do seed fertilizer or taro fertilizer, because of poor control, high concentration of urea will affect seed germination and root growth. If it is necessary to apply fertilizer, separate it from the seed, and the amount of urea should not be much. The grain crops should be applied with about 5 kg of urea. It must be mixed with dry fine soil first, and applied about 2 cm below the seeds, or about 10 cm from the side.
(1) Base fertilizer. Take grain crops as an example. Generally, 10-15 kg of urea is used in mu. First, when the dry fertilizer is used as the base fertilizer, the urea can be applied to the field and then cultivated. The spring planting crops have low ground temperature. If the amount of urea concentrated strips is not too large, it will easily cause local alkalization or biuret increase, resulting in burning. Second, when the paddy field is based on fertilizer, urea can be applied after draining the field water, then plowing, and after 5 to 7 days, the urea is converted into ammonium carbonate, and then the water is poured into the field. It is also possible to maintain shallow water application before ploughing, and then use tractors to plough to mix urea and mud evenly. In addition, when urea is used as a noodle fertilizer, the amount of mu is 7-8 kg, which is evenly applied before transplanting rice, and it is not allowed to release water in the process of polder.
(2) Topdressing. The grain crops are used with 8 to 13 kilograms of urea, and are applied during the tillering or jointing period. First, dryland crops can be applied by ditch or acupoints, and the depth of fertilization is 6-10 cm. After fertilization, the soil cover is tight to prevent the evaporation of ammonia after hydrolysis. Second, the paddy field crops should be drained first, and the thin water layer should be kept. After the application, the plants should be weeded and weeded. Do not fill the water for two or three days, and then refill all the urea after it is converted into ammonium carbonate. Topdressing with urea is a few days ahead of other nitrogen fertilizers. In the sand land, water leakage and leakage are more serious, and can be applied in different times, and the amount of fertilizer should not be too much.
Urea is easy to move with water. It can also be applied to the soil in the dry land, and then watered. In the first week, the fertilizer moves to the lower layer. Later, due to the evaporation of water, the fertilizer moves to the upper layer, and most of it is concentrated in the l0-20cm soil layer. Within, it will not cause loss of nitrogen volatilization. The amount of irrigation water should not be too large or too small. The soil should be 20-30 cubic meters, and the sandy loam or sand should be 15-20 cubic meters.
Urea is applied to other crops, and the application rate and application period are different, but the matters to be noted in the application are the same.
Urea properties and application techniques
Urea is an amide nitrogen fertilizer, accounting for 35%-40% of China's nitrogen fertilizer production, second only to carbonamine.
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