Author
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Leytem, April |
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MAGUIRE, R - N. CAROLINA STATE UNIV. |
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Submitted to: INOSITOL PHOSPHATES: LINKING AGRICULTURE & ENVIRONMENT CAB INT
Publication Type: Book / Chapter Publication Acceptance Date: 1/1/2007 Publication Date: 3/1/2007 Citation: Leytem, A.B., Maguire, R.D. 2007. Environmental implications of inositol phosphates in animal manures. In: Turner, B.L., Richardson, A.E., Mullaney, E.J., editors. Inositol Phosphates: Linking Agriculture and the Environment. 1st edition. Cambridge, MA:CAB International. p. 150-168. Interpretive Summary: Over-application or mismanagement of manure can degrade surface and groundwater quality with excess nutrients. Phosphorus (P) is a particular problem, because it can accumulate in soil to concentrations above those needed for optimum crop production. As a result long-term manure application to agricultural land leads to soil P accumulation and an acceleration of P transfer in runoff to water bodies. This process can contribute to eutrophication in freshwater ecosystems, and numerous examples of water quality impairment associated with P pollution from animal operations now exist. The environmental fate of P in animal manures is partly determined by its chemical composition, yet few studies have examined differences in the manure P composition and its effect on P reactivity in soils. Studies have indicated that in many cases manure P is predominately in inorganic forms, followed by monoester P, phospholipids, pyrophosphate and in some cases phosphonates and diester P. The phytic acid content of manures has been shown to range from non-detectible in many ruminants up to 80% of total P in manures from mono-gastric animals fed corn-soy based diets. To address concerns over surpluses of P in manure, strategies involving dietary manipulation are being widely adopted to reduce P concentrations in manures. For monogastric animals that cannot digest phytic acid, such strategies include the isolation of mutant grains having low phytic acid concentrations and supplementation of animal diets with microbial phytase to increase phytic acid hydrolysis in the gut or a combination of the two. In addition to reducing the concentrations of P in manure, dietary modification is expected to influence manure P composition, which may have implications for the environmental fate of manure P. Concerns over the potential negative environmental implications of diet alteration on P losses from manure amended soils seem to be unfounded. A review of the current literature showed the greatest benefit that is derived from diet modification to be a reduction in total P excreted by the animals by feeding closer to the animal requirements or enhancing the P availability of plant-based feed ingredients. The use of low phytic acid grains in mono-gastric animals has been shown to reduce total P excretion in swine, poultry and trout. This decrease in total P is sometimes accompanied by a decrease in phytic acid excretion, but in other instances there are no significant differences in phytic acid excretion irrespective of diet. The addition of phytase to mono-gastric diets also reduces total P excretion and phytic acid excretion in some instances, that appears to vary between species. There can also be changes in the WSP fraction of manures from both low IP and phytase amended diets. Whether this fraction increases from diet modification or decreases is in part dependent on feed formulation and the concentrations of dietary P relative to the animals requirement, but in most cases there is a decrease in soluble P excretion by the animals. Compared to traditional diets, altering animal diets has not been shown to significantly increases extractable soil P when manures were land applied on an equivalent P basis. However, if manures are applied on an equivalent weight or nitrogen basis, diet modification will result in less total P being added to soils and therefore a reduction in soil test P buildup over time which in turn decreases the risk of P transfer to water bodies. Additionally, there is little evidence that P losses in runoff from soils amended with manures from modified diets will be significantly greater than from normal diets when these are applied on an equivalent P basis (surface application or incorporation of manures). This suggests that there is little environmental risk, and some benefits, associated with changes in manure P speciation a Technical Abstract: Over-application or mismanagement of manure can degrade surface and groundwater quality with excess nutrients. Phosphorus (P) is a particular problem, because it can accumulate in soil to concentrations above those needed for optimum crop production. As a result long-term manure application to agricultural land leads to soil P accumulation and an acceleration of P transfer in runoff to water bodies. This process can contribute to eutrophication in freshwater ecosystems, and numerous examples of water quality impairment associated with P pollution from animal operations now exist. The environmental fate of P in animal manures is partly determined by its chemical composition, yet few studies have examined differences in the manure P composition and its effect on P reactivity in soils. Studies have indicated that in many cases manure P is predominately in inorganic forms, followed by monoester P, phospholipids, pyrophosphate and in some cases phosphonates and diester P. The phytic acid content of manures has been shown to range from non-detectible in many ruminants up to 80% of total P in manures from mono-gastric animals fed corn-soy based diets. To address concerns over surpluses of P in manure, strategies involving dietary manipulation are being widely adopted to reduce P concentrations in manures. For monogastric animals that cannot digest phytic acid, such strategies include the isolation of mutant grains having low phytic acid concentrations and supplementation of animal diets with microbial phytase to increase phytic acid hydrolysis in the gut or a combination of the two. In addition to reducing the concentrations of P in manure, dietary modification is expected to influence manure P composition, which may have implications for the environmental fate of manure P. Concerns over the potential negative environmental implications of diet alteration on P losses from manure amended soils seem to be unfounded. A review of the current literature showed the greatest benefit that is derived from diet modification to be a reduction in total P excreted by the animals by feeding closer to the animal requirements or enhancing the P availability of plant-based feed ingredients. The use of low phytic acid grains in mono-gastric animals has been shown to reduce total P excretion in swine, poultry and trout. This decrease in total P is sometimes accompanied by a decrease in phytic acid excretion, but in other instances there are no significant differences in phytic acid excretion irrespective of diet. The addition of phytase to mono-gastric diets also reduces total P excretion and phytic acid excretion in some instances, that appears to vary between species. There can also be changes in the WSP fraction of manures from both low IP and phytase amended diets. Whether this fraction increases from diet modification or decreases is in part dependent on feed formulation and the concentrations of dietary P relative to the animals requirement, but in most cases there is a decrease in soluble P excretion by the animals. Compared to traditional diets, altering animal diets has not been shown to significantly increases extractable soil P when manures were land applied on an equivalent P basis. However, if manures are applied on an equivalent weight or nitrogen basis, diet modification will result in less total P being added to soils and therefore a reduction in soil test P buildup over time which in turn decreases the risk of P transfer to water bodies. Additionally, there is little evidence that P losses in runoff from soils amended with manures from modified diets will be significantly greater than from normal diets when these are applied on an equivalent P basis (surface application or incorporation of manures). This suggests that there is little environmental risk, and some benefits, associated with changes in manure P speciation a |
