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United States Department of Agriculture

Agricultural Research Service

Title: Co-Amednments to Modify Phosphorus Extractability and N:p Ratio in Feedlot Manure and Composted Manure

Author
item DAO, THANH

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 1999
Publication Date: N/A

Interpretive Summary: Traditionally, animal manure applications are made to fulfill the nitrogen (N) needs of a crop. A narrow nitrogen to phosphorus ratio exists in manure. The imbalance creates a high loading of P which progressively accumulate in the soil. High P loading may affect trace mineral nutrition and may result in offsite movement. Non-hazardous industrial by-products such as alum or calcium, aluminum, iron-rich compounds such as caliche or fly ash, a coal combustion by-product of local power plants were used to induce changes in P extractability in manure and manured soils. Caliche, alum, and fly ash decreased water-extractable P and plant-extractable P in stockpiled and composted manure. Mixing these amendments with manure widened the effective N to P ratio of treated manure by 1.5 to 18. The amendments account for a small increase in pH and salts in treated soils. Thus, joint applications of animal and mineral by-products reduce excessive eamounts of P in manure and changed the treated manure into a balanced source of plant nutrients for crop production. The joint uses would reduce the stockpiling of both by-products where they co-exist within short hauling distances. Loading rates of manure on different soils and landscapes can revert back to N needs of the plant without causing environmental problems. Regulatory policies must not be focused on total P loading, but based on solubility and forms in which P moves during runoff and leaching.

Technical Abstract: Co-applications of non-hazardous agricultural, municipal, or industrial by-products potentially reduce excessive soluble P in manure and manure-amended soils and widen the effective N:P ratio in manure. I determined the effects of alum, powdered caliche, and Class C fly ash on extractable P concentrations in cattle (Bos taurus) manure and composted manure. Combinations of manure and amendments were also added to an Aridi Paleustalf and a Torrertic Paleustoll at the rate of 10 g manure kg**-1 soil. Caliche, alum, and fly ash decreased water-extractable P (WP) in stockpiled manure by 21, 60, and 85% and by 50, 83, and 93% in composted manure at 0.1g g**-1 rate of amendment. Alum and fly ash also significantly decreased Bray-I and Melich-III P concentrations by 75 and 90% in stockpiled and composted manure, respectively, and more than 90% at 0.25 or higher rates of amendment. Fly ash consistently reduced extractable eP fractions from the treated-manure in both soils. Alum and caliche achieved a constant reduction in the WP fraction only. Changes in soil pH and electrical conductivity (EC) were primarily attributed to the addition of manure or compost. The amendments may account for a small increase of 0.1 pH unit and 0.1 dS m**-1 in EC. The joint uses of mineral and animal by-products would reduce the stockpiling of both by-products. The loading rates of manure on different soils and landscapes may revert back to fulfilling N requirements of the vegetation without causing environmental quality impairments.

Last Modified: 7/28/2014
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