Plant Nutrient and Economic Value of Animal Manures

Animal manures have economic value as plant nutrient sources and as amendments for soils whose physical properties can be improved by adding organic matter. Their value as fertilizer per metric ton applied is generally inverse to their water and carbon contents. Plant nutrient concentrations in animal manures are highly variable, thereby introducing uncertainty into meeting plant nutrient needs for crop production. Where manure has been applied for several years, however, little or no additional fertilizer phosphorus (P) and potassium (K) are needed for crop production. Animal manures were ranked in decreasing order as to replacement fertilizer value (dollars) as follows: broiler litter; hen litter; hen droppings; beef feedlot, swine and dairy solid manures; poultry slurry; and other classes of livestock manure slurries. Storage conditions and degree of dilution mainly determine the fertilizer value of liquid manure. Liquid manures have little potential economic value as fertilizer outside the farm where produced. Relative efficiencies of manure nitrogen (N) as compared to commercial fertilizer N range from less than 30% to greater than 100%. Manure N applications that are immediately incorporated have produced yields equal to those produced by fertilizer N for many different crops. The representative plant nutrient contents selected from the literature suggest that replacement fertilizer value can exceed waste management costs, thus changing manure from a waste to a resource