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United States Department of Agriculture

Agricultural Research Service

Title: Phosphorus Extractability of Soils Amended with Stockpiled and Composted Cattle Manure

Authors
item Schwartz, Robert
item Dao, Thanh

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2004
Publication Date: April 20, 2005
Citation: Schwartz, R.C., Dao, T.H. 2005. Phosphorus extractability of soils amended with stockpiled and composted cattle manure. Journal of Environmental Quality. 34:970-978.

Interpretive Summary: Soils are most often the resource used in the final assimilation of many agricultural waste products. Manure and synthetic fertilizer vary in their contributions to soluble and extractable forms of P when applied to soils. Knowledge of these source and soil-dependent effects is required for planning fertilizer applications so that soil test P remains below threshold levels. This study investigates the influence of soil characteristics, manure characteristics, and fertilizer application rates on the extractability of phosphorus in amended soils incubated under controlled environmental conditions. Five selected soils of the Southern High Plains were amended with fed cattle manures, composted manure, and inorganic fertilizers at five rates and incubated under controlled laboratory conditions. Water extractable P and several agronomic soil P tests were determined for the soils after selected incubations periods. The increase in extractable P in soils amended with manures and synthetic fertilizers varied considerably with respect to P source, incubation time, extractant, and soil characteristics. Calcareous soils and soils with a high cation exchange had the lowest P extractability. Soils amended with synthetic fertilizers had significantly greater water extractable P than soils amended with manures, especially after short, one-week incubation periods. Increases in water extractable P relative to increases in agronomic soil test P were greatest for synthetic fertilizers as compared to composted or stockpiled manures. Consequently, the common agronomic soil extractants in the region cannot always be used to make reliable inferences about water extractable P, an important quantity when considering offsite movement of P with runoff. These inconsistencies could be overcome by applying both an agronomic and environmental soil test to P indexing systems so that both the soils capacity to supply P and readily soluble P are considered.

Technical Abstract: Manure and synthetic fertilizer vary in their contributions to soluble and extractable forms of P when applied to soils. Knowledge of these source and soil-dependent effects is required for planning fertilizer applications so that soil test P remains below threshold levels. The objective of this study was to evaluate the influence of soil and manure characteristics and application rates on the extractability of phosphorus in amended soils. Five selected soils of the Southern High Plains were amended with fed cattle manures, composted manure, and inorganic fertilizers [Ca(H2PO4)2 and KH2PO4] at five rates and incubated under controlled laboratory conditions. Mehlich 3, Olsen (NaHCO3), TAM (Texas A&M extractant), and water extractable P were determined for the soils after selected incubations periods. Except for the TAM and some water extractions, P extractability as a function of total P applied was linear (P<0.001) over a wide range of application rates. Phosphorus extraction efficiencies (Peff) averaged 19 percent greater for the KH2PO4 as compared to Ca(H2PO4)2 amended Pullman soil. Mehlich 3, NaHCO3, and water P extraction efficiencies of KH2PO4 amended soils were significantly (P</=0.036) greater than efficiencies of soils amended with manures except for a calcareous soil and a soil with a large amount of exchangeable Ca2+. The calcareous soil and soils with high cation exchange (CEC > 15 cmolc kg-1) tended to have significantly lower Peff principally for the TAM and water extractions. Phosphorus extraction efficiencies decreased with time for KH2PO4 amended soils (P<0.05) but remained stable or increased for manure amended soils during the eight week incubation period. Changes in water extractable P per unit increase in Mehlich 3, NaHCO3, and TAM extractable P averaged 153 percent greater for KH2PO4 as compared to composted and scraped manure amended soils. These source-dependent relationships limit the use of agronomic soil extractants to make inferences about water extractable P and dissolved P in runoff.

Last Modified: 12/22/2014
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