Why do we store manure?

Charles Fulhage, Extension Agricultural Engineer, University of Missouri; John Hoehne, MidWest Plan Service, Iowa State University

The capability to store manure reduces or eliminates the need to collect, remove and spread manure on a daily basis. In past years, when livestock operations were smaller, daily hauling or very short-term storage with frequent hauling was a common and manageable system. However, as operations increased in size and manure management systems evolved from solid or semisolid systems to liquid systems, the need for storage became more pronounced.

The primary reason to store manure is to allow the producer to land spread the manure at a time compatible with the climatic and cropping characteristics of the land receiving the manure. Manure nutrients can be best utilized when spread near or during the growing season of the crop. Therefore, the type of crop and method of manure application are important considerations in planning manure storage facilities. For example, manure applied to a corn crop with a tankwagon or injection system needs to be applied in the fall after the crop is harvested, in the spring prior to planting, or both.

Spring application is preferable because it is closer to the crop’s growing season. If irrigation from a lagoon is the application method, then manure might be spread on the growing plants. Forage or hay crops generally provide the greatest flexibility in planning land application operations. Cool season grasses can generally utilize manure nutrients from early spring to late fall, and application equipment generally does not adversely affect the crop regardless of its growth stage. In warmer regions, cropping scenarios might be developed that provide growing plants during a major portion of the year (double or triple cropping).

Climate and associated soil conditions are additional factors that strongly influence the storage period needed for manure. Saturated, wet, frozen or snow-covered soil conditions are not suitable for land application of manure. Some states may prohibit, by regulation, spreading manure on saturated, frozen or snow-covered soil. Therefore, a manure storage structure should be sized to provide a storage period compatible with the required cropping operations (tillage, planting, harvesting) and climatic conditions expected at the production location.

While crop schedules and soil or climatic conditions are the most critical factors in manure storage, other considerations may also be important:

•Soil compaction

Large manure hauling and application equipment may cause excessive soil compaction under certain soil moisture conditions. If sufficient storage is available, application operations can be performed when soil moisture conditions minimize the effects of compaction.

•Odors

Sufficient manure storage may allow spreading operations to be scheduled when odor risks influenced by wind direction and temperature or humidity conditions are minimized.

•Labor and equipment availability

While the same labor is required annually to spread manure, that labor and equipment may be available only during certain times of the year due to other needs (planting, harvesting). Therefore, a manure storage period is needed so labor and equipment can be utilized when available.

Table 1 summarizes some conditions and characteristics associated with different lengths of storage period time for manure. The actual size of manure storage structure needed depends upon the:

•volume of manure and wastewater produced

•storage period needed based on the considerations described above

Primarily, animal species and number determine manure volume. Wastewater volume depends upon many sources such as rainfall, runoff from open lots, washwater used in the buildings and fresh water used for flushing or pit recharge. The length of storage period needed depends primarily on cropping schedules, soil and climatic conditions and labor and equipment factors noted above. Most operations utilizing a single, full-season annual row crop or small grain crop will need at least six months manure storage to schedule land spreading around cropping operations.

Experience has shown that even a full year’s storage is beneficial when wet conditions may make fall application difficult and manure needs to be stored until spring. Land application operations using irrigation usually benefit from a full year’s storage so effluent can be applied during the typical irrigation season. Shorter storage periods may be acceptable in milder climates and where forage crops are utilized for receiving manure. ANM

—From Livestock and Poultry Environmental Stewardship Curriculum