Garden soils need organic matter to hold moisture, slowly release nutrients, add to soil tilth so roots can be cozy and get at soil particles... There are lots of horse stables and pastures where I live in N. Central Florida, as well as high temperatures which lead to fast decomposition of organic matter in these sandy well-drained soils, so my garden needs a healthy - pow! - shot of nutritious organic matter every fall.
Horse farmers have huge piles of free horse manure, urine and straw that get cleaned out of stables that can get them in trouble with the department of environmental protection because of the nitrogen that can leach out and go to creeks and streams in heavy rains. USDA or state agents go on visits to farms to see how their poop piles are doing, and the smaller they are the better.
This instructable tells you how to
1. find free fresh horse manure
2. get it to your house
3. add it to your soil as a mulch, or as a soil amendment for future plants.
You will need:
1. station wagon OR pickup truck with some big tarps
2. a few shovels
3. a hearty friend who likes poop
4. recycle bins or wheelbarrow
The best bet is to find a horse boarding stable, as they have lots of horse owners coming in and out... call or drive up and ask if they have some manure they'd like to get rid of. You'd be willing to remove their waste problems for free. If you're lucky, you'll find some composted manure. (Some pay to have it hauled to a landfill, or spend energy and tractor time composting it.)
A 1000-lb horse creates 50 lbs of poop and pee per day!