Closed-tank liquid manure spreaders generally have the shape of a cylindrical horizontal tank, and volume is expressed by the manufacturer in gallons. In these cases, volume is calculated in a manner similar to that shown in Figure 2. All liquid manure information is calculated on a per gallon basis. The computation of pounds of nutrients per load is found by multiplying the number of gallons per load by the pounds of nutrients per gallon. All solid and semisolid manure information is calculated on a per ton basis, which requires converting from volume measure to weight measure.
Bulk density is largely dependent on moisture content of the manure.
For example, a spreader load of poultry litter at 20 percent moisture content will be considerably heavier than the same spreader load at 10 percent moisture content. Yet, volume is approximately the same in both cases. One way to determine bulk density is to weigh the loaded spreader, then divide this weight by the spreader volume. However, scales are usually not available on-site, and another means of obtaining bulk density is needed. An alternate method of obtaining bulk density involves weighing a known manure volume then using this information with volumetric spreader capacity to obtain spreader capacity in tons.