Reproduced from Journal of Environmental Quality. Published by ASA, CSSA, and SSSA. All copyrights reserved. Freeze–Thaw Effects on Phosphorus Loss in Runoff from Manured and Catch-Cropped Soils Marianne E. Bechmann,* Peter J. A. Kleinman, Andrew N. Sharpley, and Lou S. Saporito ABSTRACT they incorporate available soil nutrients into their bio- mass, hence the name catch crop, lowering the amount Concern over nonpoint source P losses from agricultural lands to of N available to leaching within the rooting zone. In surface waters in frigid climates has focused attention on the role of addition, catch crops have been shown to decrease soil freezing and thawing on P loss from catch crops (cover crops). This erosion potential and associated particulate P losses 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 estab- compared with autumn plowed soils and even compared lished catch crop of annual ryegrass (Lolium multiflorum L.). Experi- with soils under minimum tillage (Sharpley and Smith, ments were conducted to evaluate changes in P runoff from packed 1991; Lundekvam et al., 2003). soil boxes (100 by 20 by 5 cm) and P leaching from intact soil columns The benefit of catch crops to dissolved P transport is (30 cm deep). Before freezing and thawing, total P (TP) in runoff from less clear than for erosion and nitrate N leaching, with catch-cropped soils was lower than from manured and bare soils due to some authors suggesting that catch crops may even in- lower erosion. Repeated freezing and thawing significantly increased crease dissolved P losses (Uhlen, 1989; Børresen and water-extractable P (WEP) from catch crop biomass and resulted in Uhlen, 1991). The basis for this opinion is that catch significantly elevated concentrations of dissolved P in runoff (9.7 mg crops concentrate P above ground, some of which may L -1 ) compared with manured (0.18 mg L -1 ) and bare soils (0.14 mg L -1 ). become available to runoff. Under field conditions, an- Catch crop WEP was strongly correlated with the number of freeze– thaw cycles. Freezing and thawing did not change the WEP of soils nual ryegrass, a common catch crop in northern agro- mixed with manures, nor were differences observed in subsurface losses ecosystems, contains 1.7 to 7 kg ha -1 of total P (TP) (Ule ´n, of P between catch-cropped and bare soils before or after manure 1997; Molteberg and Tangsveen, 2002), with 60 to 80% application. This study illustrates the trade-offs of establishing catch of plant P in inorganic form (Jones and Bromfield, 1969; crops in frigid climates, which can enhance P uptake by biomass and Sharpley and Reed, 1982). Annual ryegrass contains more reduce erosion potential but increase dissolved P runoff. P than other less common catch crops, like white clover (Trefolium repens L.) and fescue grass (Festuca pratensis Huds.) (Miller et al., 1994; Sturite and Henriksen, 2002). T he control of nonpoint-source nutrient pollution, Furthermore, Pierzynski and Logan (1993) found differ- particularly P and N, represents a major environ- ences in the ability of various crops to recover soil P, mental challenge for agriculture in Europe and North resulting in a range of aboveground biomass P. America due to widespread problems of surface water Under certain conditions, the inorganic P in catch crops eutrophication and ground water contamination (Car- may be released to water, contributing to the transfer of penter et al., 1998; Withers and Lord, 2002). Large gains P to surface waters (Timmons et al., 1970; Sharpley and have been made in implementing management practices Smith, 1991; Miller et al., 1994). Miller et al. (1994) showed to reduce losses of individual nutrients from agricultural that much inorganic P was leached from ryegrass catch soils, but successful control of one nutrient may uninten- crops exposed to simulated rainfall after freezing, but tionally exacerbate losses of another. only minimal organic P was leached. Gburek and Broyan Catch crops, synonymous with cover crops, are wide- (1974) compared sequential laboratory leachings of or- spread in Scandinavia, where they have been heavily pro- chardgrass (Dactylis glomerata L.) with seasonal differ- moted for water quality protection (Ule ´ n, 1997; Molte- ences in water quality in a watershed in Pennsylvania berg and Tangsveen, 2002). For instance, since 1999 in and concluded that contributions of dissolved P from Norway, there has been an increase in subsidies allo- vegetation could account for elevated concentrations of cated to farmers to plant catch crops (Lundekvam et al., P in runoff. Elsewhere, Sharpley (1981) found that an in- 2003). The primary objective of promoting catch crops crease in the age of cotton (Gossypium hirsutum L.), sor- is to minimize nitrate N leaching after summer crops ghum (Sorghum sudanense Stapf.), and soybean [Gly- have been harvested (Meisinger et al., 1991; Bergstro ¨m cine max (L.) Merr.] resulted in greater contributions and Jokela, 2001). Because catch crops are unfertilized, of dissolved P from plant leaves to runoff, accounting for increases in runoff P by 20 to 60%. In cold climates, freezing and thawing can play an ad- M.E. Bechmann, Norwegian Centre for Soil and Environmental Re- ditional role in dissolved nutrient transport. Each freez- search, Jordforsk, Frederik A. Dahls vei 20, N-1432 Aas, Norway; and P.J.A. Kleinman, A.N. Sharpley, and L.S. Saporito, USDA-ARS, Pas- ing event damages plant cells, with lysed cells potentially ture Systems and Watershed Management Research Unit, Curtin releasing dissolved P (White, 1973; Uhlen, 1989). For in- Road, University Park, PA16802-3702. Received 8 Nov. 2004. *Corre- stance, in a field experiment Børresen and Uhlen (1991) sponding author (marianne.bechmann@jordforsk.no). observed an increase in the concentration of dissolved Published in J. Environ. Qual. 34:2301–2309 (2005). Technical Reports: Surface Water Quality Abbreviations: DRP, dissolved reactive phosphorus; FTC, freeze/thaw cycle; ICP-AES, inductively coupled plasma–atomic emission spec- doi:10.2134/jeq2004.0415  ASA, CSSA, SSSA trometry; SS, suspended solids; TP, total phosphorus; WEP, water extractable phosphorus. 677 S. Segoe Rd., Madison, WI 53711 USA 2301 Published online November 7, 2005