Question
My lemons do not grow well. I do not know fertilizer doses necessary for lemon tree. My garden is four years old. Please inform me about recommended NPK dose time of application and way of application and recommendation for farm yard manure application

Answer
Greetings, Citrus are heavy feeders.  Your fertilizer should be tailored to your needs and without a soil test, I can't make an exact recommendation.  They also need full sun, lots of water and perfect drainage.  When in doubt, a general purpose, equal amount  (8-8-8 or 20-20-20) fertilizer should produce a crop, maybe not an optimal crop, but still good fruit.  Fertilize at the beginning of your growing season with two additional applications 45 days apart.
Manure must be well composted before being used.  If it's still "hot", it will rob your nitrogen.  Once composted, a light application watered in, or incorporated at planting, will benefit your plants. Compost can be applied anytime. Jim