Billy wrote:
Then there is that other stuff about not adding too much for fear of
burning the roots of your plants.

Good point. That applies to horse "manure" in the sense of straw or
wood shaving stall bedding. Urine is very high in available nitrogen.
Urine-soaked stall bedding can burn plant roots by delivering a surge
of excess nitrogen.

Horse feces have an ideal C:N ratio and by themselves will not burn
plant roots. Many horse farms and stables pick feces daily and strip
bedding weekly, so by knowing their cleaning schedule you may be able
to select "manure" that has relatively more or less nitrogen.

Una