|Bechmann, M - NORWEGIAN CNTR FOR SOIL|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2005
Publication Date: November 7, 2005
Citation: Bechmann, M., Kleinman, P.J., Sharpley, A.N. 2005. Freeze-thawing effects on phosphorus loss in runoff from manured and catch-cropped soils. Journal of Environmental Quality. 34:2301-2309. Interpretive Summary: Phosphorus runoff from agricultural soils has been implicated in accelerated eutrophication, the biological enrichment of surface waters that is a water quality problem world-wide. In northern climates, the use of cover crops has been steadily gaining ground, especially in Scandinavia where they are referred to as 'catch crops' for their intended role in taking up excess soil nutrients and catching eroded particles of nutrient-rich surface soil. There has been, however, some concern that catch crops can enrich surface runoff with dissolved phosphorus in spring runoff. This study evaluated the effect of freezing and thawing on the fate of phosphorus in runoff from soils with and without an established catch crop. Repeated freezing and thawing significantly increased water extractable phosphorus in catch-crop biomass and resulted in greater concentrations of dissolved phosphorus in runoff (9.7 mg L-1) than in the manured (0.18 mg L-1) and bare soils (0.14 mg L-1). This study highlights the trade-offs of establishing catch crops, which can enhance P uptake and reduce erosion but increase dissolved P in runoff.
Technical Abstract: Concern over non-point source phosphorus (P) losses from agricultural lands to surface waters in frigid climates has focused interest on the effects of freezing and thawing on P loss in overland and subsurface flow. This study evaluated the effect of freezing and thawing on the fate of P in bare soils, soils mixed with dairy manure, and soils with an established catch crop of annual ryegrass (Lolium multiflorum L.). Experiments were conducted to evaluate changes in soil P runoff from packed soil boxes (100 x 20 x 5 cm), and leachate from intact soil columns (30-cm deep). Prior to freezing and thawing, total P (TP) in runoff from catch-crop treatments were lower than for manured and bare soil, due to less erosion. Repeated freezing and thawing significantly increased water extractable P (WEP) in catch-crop biomass and resulted in greater concentrations of dissolved P in runoff (9.7 mg L-1) than in the manured (0.18 mg L-1) and bare soils (0.14 mg L-1). The number of freeze/thaw cycles was strongly correlated with catch-crop WEP. Subsurface losses of P were lower for the catch crop before freezing than for bare soil, while manure addition increased the leached P. Freezing reduced leachate TP concentrations. This study highlights the trade-offs of establishing catch crops, which can enhance P uptake and reduce erosion but increase dissolved P runoff. As the risk of P runoff from catch-cropped soils can increase with number of freeze/thaw cycles, catch-crop management is critical to minimize the risk of P loss.