You can make a useful manure spreader from your old box trailer. Just add a movable tailgate hinged at the top two corners instead of at the bottom and install a long horizontal auger to break up clods that turns as the wheels of the trailer turn. It will work more effectively than drop spreaders to add this natural fertilizer to your fields. Follow these directions to turn your box trailer into a manure spreader.
Step 1: Remove the Tailgate and Reattach it to the Side Trailer Walls
Unscrew the tailgate from its bottom hinge and add new hinges to attach it to the side walls. Ensure it can move outward from the back of the trailer with a slight push.
Step 2: Attach the Auger to the Axle Beams
Attach the auger at each end to an L-shaped axle beam with long metal screws fastened so the auger can rotate. Fasten each axle beam to one of the rear wheels of the trailer so that when the wheels turn, the auger will turn too. The auger, a long screw-vaned pole, will break up the clods of manure so they fall as smaller pieces onto the field.
Step 3: Fill the Trailer with Manure and Test the Spreader
Shovel the manure into the trailer from the rear to the front. Keep the shovel in the trailer while spreading the dried manure. Attach the trailer to the truck or other vehicle that will convey it to the field. Your assistant can climb into the trailer wearing suitable rubber boots, and using the heavy rake, push the manure forward through the tailgate and onto the auger. Keep the trailer moving to rotate the auger. Travel at the speed you would use for mowing the lawn, about 5 miles per hour. Test the spreader to see if the manure exits the tailgate effectively. Pay attention to whether or not the auger turns fast enough to chop it up and check to see if the auger clogs up.
Step 4: Declog the Auger
As you turn the truck and trailer to go down a new row, stop and declog the auger with the rake. Shovel up the manure released from the auger and put it back in the trailer.
Step 5: At the End of the Day
Park the trailer near a garden hose or pressure washer. Tilt the tailgate up and prop it open. Hose out the back of the trailer. If you prefer, collect the liquid residue in a barrel to add to the vegetable garden from time to time. Rinse off the auger with the pressure washer as well to prevent hardening of the manure residue on it.
In winter, use it to spread sand down your driveway for traction.