Certified GKH Gardening Expert
This article should help you with that: https://www.gardeningknowhow.com/edible/fruits/citrus/fertilizing-citrus-trees-best-practices-for-citrus-fertilizing.htm
I have had great success with lemon trees with: water, feed with liquid manure, usually comfrey, mulch with seaweed, stable straw or horse manure and water again. I do this 3 monthly. Be very careful that mulch does not touch the trunk.