The top-dressing of crops is an important means to increase production and income, but it is necessary to pay attention to science when top-dressing, so as to achieve a multiplier effect. To adapt to local conditions. Because the structure of the soil is different, it is necessary to carry out necessary tests on the soil during fertilizer application, and determine the type of chemical fertilizer to be applied according to the difference in soil acidity and alkalinity. Under normal circumstances, the use of acidic fertilizers such as ammonium sulfate in low-alkali soils; acid soils such as urea, ammonium bicarbonate, ammonia, etc.; alkaline or neutral fertilizers; sand and sandy loam with poor water retention and fertility must be applied to prevent evaporation. Ammonium chloride, urea and other fertilizers. At the same time during the top-dressing period, it is best to increase the frequency of topdressing and reduce the amount of fertilizers each time to prevent evaporation and loss of chemical fertilizers. It should be due to fertilizer. Most chemical fertilizers are salts, which are acidic, alkaline, and neutral. When fertilizing, it must be treated differently depending on the nature and composition of the chemical fertilizer. Ammonium chloride and urea can be mixed and applied to paddy fields to inhibit nitrification and reduce leaching loss, but they must not be used in saline soils to prevent chlorides from accumulating in the soil and increase salt damage. At the same time can not be applied to tobacco, sugar beet and potato and other chloride-resistant crops, so as not to reduce its yield and quality; urea applies to all kinds of crops and all kinds of soil, but it can only be released in the soil through the transformation of fertilizer efficiency, absorbed by crops . Therefore, when using urea as topdressing, it is necessary to advance several days ahead of other nitrogenous fertilizers, and at the same time apply deep soil and improve fertilizer efficiency. It is necessary to adjust the situation. Different types of crops are even different varieties of the same crop, and the type and amount of chemical fertilizer required are different. Therefore, according to the type of crops, the right medicine should be supplied on demand. For example, 230-370 kg of ammonium sulfate or 180-200 kg of urea can be topdressed per hectare of rice; corn and sorghum require more nitrogen, and the application of base fertilizer and seed fertilizer alone cannot always meet the requirements of crops for nitrogen fertilizer, but also make up for a certain amount in time. The nitrogen fertilizer, topdressing 150-190 kg of urea per hectare; soybeans also need more nitrogen fertilizer crops, nodules and nitrogen fixation can only meet the need for about 50% of the nitrogen fertilizer in the whole growth period of soybean, timely topdressing nitrogen fertilizer effect is very good. Each hectare can be weighed 130-170 kilograms of urea; sunflower due to high plant height, deep roots, large flower disk, the amount of fertilizer required is also higher than the cereal crops, each hectare can be applied 170-190 kg of urea. It is necessary to adapt to the times. The key issue of topdressing is to grasp the critical period and the maximum efficiency period of nutrients for various types of crops, so that topdressing can be carried out during the peak season of nutrition. The jointing and heading of sorghum is the period between vegetative growth and reproductive growth. At this time, the absorption of nutrients reaches the highest peak, which is the best time to top-dressing; the early-stage top-dressing of wheat has obvious yield-increasing effects, and topdressing nitrogen fertilizer should be applied at the three-leaf stage. Strong seedlings and large spikes lay the foundation; soybeans can be topdressed with nitrogen once at the early flowering stage, which can reduce the rate of falling flowers and plants, and can prolong the lifespan of plants, increase grain weight and yield; corn is absorbed after the jointing season until the big bell-mouth period. At the peak of nutrition, the first fertilizer should be topped and the second fertilizer should be applied before heading; rice should be top-dressed once during rejuvenation, jointing, and heading; millet should be top-dressed during jointing to booting; sunflowers can be in the budding stage. Top dressing. China Agricultural Network Editor
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