Foliar fertilizer, also known as top dressing, is a fertilization method in which fertilizer is dissolved in water and sprayed on the leaves of the crop. After the general fertilization, the amount of the fertilizer attached to the foliage of the plant is 30-60% of the total amount of spraying, and the amount of the crop absorbed is 40-80% of the attached amount. Pay attention to the following points when applying foliar fertilizers: (1) It is best to do it from 3pm to late evening. At this time, the temperature is low and the humidity is high, which is beneficial to the absorption of the leaves. Spraying can be done all day on cloudy days, but it should not be carried out before and after rain. (2) The leaves must be sprayed on both sides of the blade, especially the leaves with more pores. The back of the leaves must be sprayed (the absorption rate of the leaf surface is more than 1 times higher than that of the front surface). (3) Fertilizer should be fully dissolved and mixed with water before spraying. For example, when superphosphate is used, calcium superphosphate should be brewed with hot water and 24 hours later, the supernatant should be diluted with 3% and then sprayed. (4) Can be sprayed with pesticides. This can not only prevent and treat diseases and insect pests, but also achieve the purpose of fertilization, but it should be noted that phosphorus-containing fertilizers generally cannot be sprayed with pesticides containing lime. (5) Spray concentration should be appropriate. Poor concentration results in poor results and high yields of fertilizer. At the same time, the quality of fertiliser applied is better and inferior products cannot be used. For example, when the biuret content in urea exceeds 2%, foliar spray fertilizer tends to produce poisoning. (6) The nitrogen fertilizer requirement of leafy vegetables is high at each growth stage, and the nitrogen fertilizer is the main fertilizer for foliar fertilizer; the nitrogen, phosphorus and potassium needs to be balanced in fruit and vegetable; the nitrogen, phosphorus and potassium mixture should be used for foliar fertilizer; Vegetables and bulb vegetables have a good response to phosphorus and potassium fertilizers, and phosphorus and potassium are the main fertilizers for foliar application. (7) Adding urea when spraying trace elements can increase the crop absorption rate and prevent temporary yellowing of crops.