What are the methods for topdressing vegetables during the seedling stage?

    1. Topdressing time. Generally, it is best after the seedlings have all emerged and the cotyledons have flattened out; within a day, it is best from 10 to 12 a.m. on a sunny day. 2. Topdressing methods. Both chemical fertilizers and organic fertilizers can be used as topdressing; when applying chemical fertilizers, nitrogen fertilizer should be the main type, and compound fertilizer is even better. They can be broadcast first and then watered, or applied with irrigation water, or dissolved in water and splashed on, with the ratio of chemical fertilizer amount to watering amount kept at 0.1-0.3:100; if the amount of chemical fertilizer applied is too large and the concentration exceeds 0.5%, seedling burn is very likely to occur; when applying organic fertilizer, decomposed human manure or pen manure is mostly used. First dilute the fertilizer with water 10-20 times, then pour it into the seedbed; whether applying chemical fertilizer or organic fertilizer, after fertilizing, spray once with clean water to wash off the fertilizer attached to the leaves and prevent leaf burn, and ventilate and exchange air in time to prevent harmful gases (such as ammonia gas, hydrogen sulfide gas, nitrous acid gas, etc.) from escaping and harming vegetable seedlings. 3. Foliar topdressing. When the seedbed temperature is low and the seedling root system has a weak ability to absorb fertilizer, root topdressing is not suitable; instead, 0.1% potassium dihydrogen phosphate or 0.3% urea solution, or 0.2-0.3% superphosphate extract, can be sprayed on the leaves.