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Volume 36, Issue 2 p. 532-539
Surface Water Quality

Freezing and Drying Effects on Potential Plant Contributions to Phosphorus in Runoff

Tiffany Roberson

Tiffany Roberson

Dep. of Soil Science, 1525 Observatory Dr., Univ. of Wisconsin, Madison, WI, 53706-1299

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Larry G. Bundy

Corresponding Author

Larry G. Bundy

Dep. of Soil Science, 1525 Observatory Dr., Univ. of Wisconsin, Madison, WI, 53706-1299

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Todd W. Andraski

Todd W. Andraski

Dep. of Soil Science, 1525 Observatory Dr., Univ. of Wisconsin, Madison, WI, 53706-1299

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First published: 01 March 2007
Citations: 43

Research supported by the Wisconsin Dep. of Agric., Trade, and Consumer Protection, the Univ. of Wisconsin Nonpoint Pollution and Demonstration Project, and the College of Agric. and Life Sci., Univ. of Wisconsin-Madison. The senior author gratefully acknowledges receipt of an Advanced Opportunity Fellowship from the Univ. of Wisconsin Graduate School. The authors gratefully acknowledge J.S. Studnicka for technical support and contributions from the staff at the University of Wisconsin Agricultural Research Station at Arlington.

ABSTRACT

Phosphorus (P) in runoff from landscapes can promote eutrophication of natural waters. Soluble P released from plant material can contribute significant amounts of P to runoff particularly after plant freezing or drying. This study was conducted to evaluate P losses from alfalfa or grass after freezing or drying as potential contributors to runoff P. Alfalfa (Medicago sativa L.) and grass (principally, Agropyron repens L.) plant samples were subjected to freezing and drying treatments to determine P release. Simulated rainfall runoff and natural runoff from established alfalfa fields and a grass waterway were collected to study P contributions from plant tissue to runoff. The effects of freezing and drying on P released from plant tissue were simulated by a herbicide treatment in selected experiments. Soluble reactive P (SP) extracted from alfalfa and grass samples was markedly increased by freezing or drying. In general, SP extracted from plant samples increased in the order fresh < frozen < frozen/thawed < dried, and averaged 1, 8, 14, and 26% of total P in alfalfa, respectively. Soluble reactive P extracted from alfalfa after freezing or drying increased with increasing soil test P (r2 = 0.64 to 0.68), suggesting that excessive soil P levels increased the risk of plant P contributions to runoff losses. In simulated rainfall studies, paraquat (1,1′-dimethyl-4, 4′'-bipyridinium ion) treatment of alfalfa increased P losses in runoff, and results suggested that this treatment simulated the effects of drying on plant P loss. In contrast to the simulated rainfall results, natural runoff studies over 2 yr did not show higher runoff P losses that could be attributed to P from alfalfa. Actual P losses likely depend on the timing and extent of plant freezing and drying and of precipitation events after freezing.