The optimum fertilization period and fertilizer dosage for vegetables are determined according to the law of phosphorus demand. The first critical period of phosphorus demand of vegetables is dwarfing period. Phosphorus deficiency at seedling stage, short plants, slow growth, underdeveloped roots, purple leaves and tender seedlings. Therefore, when sowing vegetables, we should concentrate on applying phosphate fertilizer or base fertilizer. Zhong Bi, generally radish is applied with 15-20kg calcium phosphate or 25-40kg calcium magnesium phosphate. When using base fertilizer, the dosage can be increased appropriately. The formation period of vegetables is the second critical period when phosphorus is needed. This is the period when phosphorus is most needed. Insufficient phosphorus nutrition will seriously affect vegetable yield. Spraying 0.2% potassium dihydrogen phosphate solution or 2 ~ 3% calcium superphosphate solution on the leaves.
According to the types of phosphate fertilizer, master the use method: calcium superphosphate and calcium magnesium phosphate fertilizer are generally used. Calcium-magnesium-phosphate fertilizer is alkaline, and its application effect is good in acidic soil. Because it is insoluble in water, it cannot be used in autumn rain. After being piled with manure and other organic fertilizers, it will be better as base fertilizer or seed feed. Calcium magnesium phosphate fertilizer has a long action time, and 70% ~ 85% may remain in the soil. Therefore, as a vegetable to return to the ground, it should be implemented first and then despised. Calcium superphosphate is an acidic water-soluble phosphate fertilizer. Can be used as foundation, planting fertilizer and topdressing outside the roots. Chemical fixatives with low activity and easy to produce phosphorus in fruit acid and overbased soil must be used early, for blood and for heart. It is best to use it near the roots of vegetables. In other words, improve the efficiency of phosphorus and let vegetables be absorbed and utilized earlier.
Phosphorus in soil is very important for the growth of vegetables. Vegetables, in particular, are sensitive to phosphorus absorption before and after growth. Phosphorus has poor fluidity and is easy to be fixed, so absorption efficiency is a problem that needs to be considered in the use of phosphate fertilizer. Vegetables cultivated in protected facilities provided sufficient phosphorus with base fertilizer before planting. According to the soil test data, the soil phosphorus in the shed has reached a rich state, and some even exceeded the standard. It can be said that the phosphorus in the soil of straw shed basically meets the demand of vegetable growth.
In the early stage of vegetable growth, vegetable plants should maintain a balanced growth, that is, an appropriate root canal fee. If there is insufficient phosphorus at this time, it is easy to appear "barefoot". Phosphorus has a great influence on the growth of roots. Phosphorus in soil is insufficient or fixed, which has light influence and slow root development. The sentence "the main root is weak and the lateral root is sparse" accurately reflects the appearance of the root when phosphorus is insufficient. Vegetables don't have strong roots in the early stage of growth, let alone strong trees. When phosphorus deficiency is serious, not only the underground part grows weakly, but also the aboveground parts grow slowly, with small leaves and poor flower bud differentiation. In the middle and late period of vegetable growth, with the increase of growth and yield, the demand for phosphorus also increases. If the phosphorus supply is insufficient in the middle and late stage, the fruit will become smaller in the later stage, the middle and upper leaves will become smaller and the leaf color will become darker. In severe cases, mesophyll will turn purple, and even the veins will turn purple.