Nitrogen Supplying Capacity of Animal Manures to the Soil in Relation to the Length of Their Storage

The study estimated the relationship between the amount of nitrogen (N) that will become available to plants after incorporation of soil of sheep/goat, cattle, swine, and poultry manure and the duration of manure storage prior to soil addition. Manures were periodically sampled from 12 storage piles that were kept for 12 months each and mixed with soil before laboratory incubation for 83 days. The percentage of organic N mineralized after soil incorporation was clearly greater for poultry, ranging between 41 and 85%, in relation to the other three manure types, for which maximum mineralization ranged between 4.5 and 66%. For sheep/goat, cattle, and swine, the interaction between mineralization and immobilization processes showed a distinct pattern with two phases of net N release during the twelve months of storage. The first was separated from the second by a period where mineralization was zeroed and appeared at about six months after storage initiation. It was recommended that farmers should preferably use well-digested manures that have been aerobically stored more than six months to avoid materials that provoke intense immobilization, unless problems associated with the use of fresh manure are managed.