Well there is nitrate in your piss, it is a good source of quick nitrogen for the plants. Is it standard Miracle Grow? You want the Tomato formula really, because that is high in nitrogen and that's what the plants need for the veg stage of growth. You should really go with organic fertilizers such as manure, guano, seaweed, or any organic mix you can find at a gardening center. You but will come out a lot better tasting.