Do you need to use plant food if you are using horse manure in your garden?

I live in the Phoenix valley area and I am trying to grow a garden. Everyone keeps telling me that tomatoes are heavy feeders. I mixed sand, manure, garden soil and gypsum in my garden before I planted. The winter has been rather mild and the garden I planted in the spring of last year is still thriving except for... show more I live in the Phoenix valley area and I am trying to grow a garden. Everyone keeps telling me that tomatoes are heavy feeders. I mixed sand, manure, garden soil and gypsum in my garden before I planted. The winter has been rather mild and the garden I planted in the spring of last year is still thriving except for the watermelon and a tomato. I am not sure if I am doing anything wrong because 99% of my garden is green and healthy but that 1% is not. Every other tomato is doing well just the one died and what is weird is that it one of the ones I bought at the store. I am kind of wondering if this isn't a case of if it isn't broke don't fix it type of situation. So here are my questions: Do I need to use plant food or will the manure be enough? Can you over fertilize plants in the Phoenix valley? The soil was awful that's why I ask. Thank you for looking at my question.
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