It gives recommended tractor sizes for different sizes of spreaders. During transport to the field, the top-loading spreaders may make use of the baffles and interior agitation described earlier for vacuum spreaders. The unloading system is slightly different. There are two basic methods of emptying the spreaders, either by pumping or by gravity. The pump system employs an impeller at either the front or the rear of the spreader.
Manure enters the impeller either by gravity or by auger in the spreader.
From this point, several options are available. The impeller often forces the manure against a deflector plate giving a uniform spread pattern of a certain width. This spread pattern could be a wide band extending on either side of the line of travel. Alternatively, the pattern may be out to one side only. Farmers wanting to spread manure on standing row crops may prefer to use either drop pipes or injectors instead of broadcasting the manure onto the crop.