Nutrient release from winter cover crops exposed to freeze-thaw events

Winter cover crops are widely promoted due to their numerous soil and water quality benefits. However, recent research has highlighted some concerns about the potential leaching of phosphorus (P) and nitrogen (N) from cover crop biomass after cycles of freezing and thawing. These freezing events may cause ice crystals to form in and between plant cells which can, in turn, result in cell lysis and tissue damage, consequently inducing nutrient release. Laboratory and field experiments were done to determine the effect of freeze-thaw conditions on phosphorus release from commonly used cover crops in the U.S. Midwest. The laboratory column study included forty-eight polyvinyl chloride columns (20 cm diameter; 57 cm height) planted with one of two cover crop species: cereal rye (Secale cereale L.) or forage radish (Raphanus sativus L. var. longipinnatus). These columns were exposed to one of two freezing treatments after cover crop establishment and were then subjected to simulated rainfalls during and after which runoff and drainage samples were collected. Heavy freezing conditions created notable differences in total phosphorus (TP) and nitrate (NO3-N) concentrations in runoff and drainage water samples. The surface runoff TP treatment means for cereal rye and radish where 8 to 4 times higher (0.95 ± 0.44 and 0.63 ± 0.18 mg TP/L) than the bare soil (0.10±0.04) under the heavy freeze treatment. Nevertheless, the presence of cover crops significantly reduced NO3-N concentrations in drainage water across all freezing events, with an average N concentration reduction of 60-80%. The field study was performed at the University of Illinois ACES Dudley Smith Farm (Illinois, USA) using high frequency sampling (every 6 h) for 22 days to evaluate TP and dissolved reactive phosphorus (DRP) loss in subsurface drainage water from plots with and without a cereal rye cover crop during late winter of 2020. No difference was found between cover crop and no cover crop drainage flow volume (1,080 ± 170 and 1,130 ± 140 m3), cumulative DRP load (52 ± 19 and 61 ± 52 g DRP), or cumulative TP load (87 ± 22 and 109 ± 79 g TP, for the two treatments, respectively) over the 22 d. Taken together, these two studies illustrated that while phosphorus losses due to plant cell lysis during freezing and thawing cycles are possible, such tradeoffs of winter cover crops may be difficult to detect in larger scale studies, even using a replicated plot approach with relatively high frequency sampling as done here. Overall, the benefits of cover crops in tile drained areas of Illinois outweigh the risks of P and N loss in surface runoff.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste