Hi Aaron, my horses don't live on my property, they live at a barn nearby, where everything collected from the stalls and pastures (manure, urine, pine shavings) is mixed together and composted. I get a trailer load of this compost twice a year - in the fall I just dump it on the garden, mix it with brown components like leaves, and sow a cover crop, then in the spring I get another load 6 weeks or so before planting time, and mix it in with the dirt and add lime.
So I can't really judge the effect of horse urine by itself, but from my experience the compost mixture of manure, urine and pine shavings provides a lot of nitrogen, phosphorus and potassium for the plants, but it tends to be a bit acidic (not too acidic, since it's full of healthy red worms) so I test the soil and add lime as needed. The compost mix from my horses' barn is about 70% manure (nitrogen) 20% pine shavings (carbon) and 10% urine (potassium and phosphorus) which is pretty nitrogen-heavy.
Some people who have horses on their property, have found ways of controlling the proportions better. I've heard of people who train their geldings and stallions to pee in one place where it can be collected (like a barrel buried underground) since males tend to pee and poop as a way to mark territory, whereas mares pee wherever they are when they have to go, or it they're in heat, wherever they are are when they have a stallion's attention.
If you're collecting manure/pee/stall bedding from a local barn, depending on how much bedding they tend to use (it can vary a lot) the best thing might be to mix in more carbon and then let it compost further before you use it your garden, then test your soil.
Another thing to keep in mind, is most responsible horse owners treat their horses for parasites, with drugs like Ivermectin or Panacur, which take about six months to degrade into harmless molecules that can't harm soil microorganisms. So this is another good reason to let any compost you get from horse barns, to sit and compost further.
Watermelon was planted away from the 3 sisters due to limited space and too many vining plants already. There's two pants and they are starting to do well. There's even a flower on one vibe already. Wonder if there's more now... I'm probably going to pick some peppers today. I know there are banana peppers ready to pick. There may be jalapenos ready too. Habaneros are growing leaves and branching well but just starting to flower last I checked. I'll look today to see if there are peppers developing yet. We already picked 3 bell peppers but there's more growing. Doubt they are ready today though. They seem to take a while to develop from flower to harvest. Corn is odd this year. The 3 sisters corn (glass gem) is 6ft tall while the bodacious sweet corn is only about 3ft tall and so is the early sunglow, but the sunglow was only expected to get 4ft anyway.
