Chemical changes occur when calcium superphosphate is applied to the soil, the most prominent change being the fixation of phosphorus. In the southern acidic soil, iron phosphate and aluminum phosphate are easily precipitated, while in the northern calcareous soil, calcium phosphate precipitates, which reduces the effectiveness of the phosphate fertilizer and greatly reduces the fertilizer efficiency. This is the utilization rate of the phosphate fertilizer in the current season is not high. main reason. In addition, the phosphate fertilizer has little mobility in the soil, and the moving distance is generally 1-3 cm, and it is difficult to solve most of the concentrated fertilization points within 0.5 cm. Therefore, the principle of increasing the profitability of phosphorus is to reduce the contact between fertilizer and soil to avoid fixation, and to increase the contact between fertilizer and roots to facilitate crop absorption. The following measures should generally be taken:
(1) Centralized administration. Calcium phosphate should be applied centrally as a base fertilizer, seed fertilizer or top dressing to reduce its contact with the soil. For the cultivating crops, the method of applying the strips or applying the acupoints can be adopted, and the method of using the scorpion or the root of the stalk can be adopted in the paddy field, and the effect of the base fertilizer is generally better than the top dressing.
(2) Mixed application with organic fertilizer. Mixed application with organic fertilizer can reduce the contact between fertilizer and soil, so it can also reduce the retention of water-soluble monocalcium phosphate. In essence, organic fertilizer is used to protect phosphate fertilizer and reduce fixation.
(3) Made of granular phosphate fertilizer. The production of granular fertilizer is also a way to reduce the contact surface between phosphate fertilizer and soil, and has the same meaning as centralized application. The particle size of the granular phosphate fertilizer is generally 3-5 mm.
(4) Layered application. In the case of a large amount of phosphate fertilizer, 70% of the amount can be used as the base fertilizer, and the remaining 30% is used as the seed fertilizer to ensure sufficient phosphorus for crops in the seedling stage and in the middle and late stages.
(5) Top dressing. Top dressing is one of the ways to effectively apply phosphate fertilizer. It completely avoids the fixation of the soil to the water-soluble monocalcium phosphate. Especially in the late stage of crop growth, when the roots absorb nutrient capacity weakened, foliar application of phosphate fertilizer can increase the 1000-grain weight of rice and wheat, the weight of cotton and increase the fruit setting rate of fruit trees.
When spraying superphosphate, a small amount of water should be added to the phosphate fertilizer to prepare a mother liquor. Rotate and clarify, and the supernatant is diluted to the desired concentration and sprayed. Spray concentration should be based on crop type and growth conditions. Generally, the suitable concentration of dicotyledonous crops is 0.5%-1%, and the suitable concentration of monocotyledonous crops is 1%-2%.
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