Manure benefits crop production through its fertilizer value and enhancement of soil physical properties and overall soil quality. The fertilizer N value of manure depends on the conservation of urine N. Approximately 25 35% of the N contained in manure of ruminant livestock (beef and dairy cattle, sheep) is available to the plant the season following application vs. 50 60% for poultry and swine. As livestock and crop production become more specialized, it becomes more difficult to conserve manure nutrients and recycle them through crops. Manure N losses via ammonia volatilization, nitrate leaching, and denitri-fication, and manure P losses in runoff are the principal pollution concerns. The economics of practices that enhance manure's fertilizer value, and capture of methane during manure storage may become increasingly attractive in the current era of high energy costs.
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