Phosphorus mobilization from intact soil monoliths flooded under simulated summer versus spring snowmelt with intermittent freeze–thaw conditions

Abstract

Enhanced phosphorus (P) release from flooded, anaerobic soils has been extensively studied under summer temperatures but not under cold temperatures with intermittent freeze–thaw events. We investigated the temperature and freeze–thaw effects during flooding on the release of P to floodwater from soil monoliths (15‐cm depth) collected from eight agricultural fields in Manitoba. Soil monoliths were flooded with reverse osmosis water and incubated for 56 d under simulated summer flooding (SSF; 22 ± 1 °C) or snowmelt flooding with intermittent freeze–thaw (IFT; 4 ± 1 °C with intermittent freezing) in triplicates. Redox potential (Eh), pore water and floodwater dissolved reactive P (DRP) concentrations, pH, and concentrations of Ca, Mg, Fe, and Mn were determined weekly. In seven soils, Eh decreased rapidly with days after flooding (DAF) under SSF to values <200 mV but not under IFT. Both pore water and floodwater DRP concentrations significantly increased with DAF in all soils under SSF and in seven soils under IFT. Although DRP concentrations were consistently greater under SSF than IFT in four soils, other soils had similar concentrations at certain DAF. Significant relationships between ion concentrations and redox status that fitted both IFT and SSF data in most soils suggest that similar redox‐driven mechanisms are responsible for the P release; however, less P was released under IFT than under SSF because soils were not severely reduced under IFT. Substantial P release in a few soils under IFT appeared to be unrelated to redox status, suggesting other P release mechanisms that are not redox driven.

Phosphorus release from intact soil monoliths of manure‐amended fields under simulated snowmelt flooding

“…The Eh values in the SSM treatment reached values below 100 mV around 28 DAF and declined to negative values by about 42 DAF (Figure 1a). This rapid decline in redox potential of intact soil monoliths has been previously reported with flooding of soil monoliths (Shaheen, Rinklebe, Rupp, & Meissner, 2014;Weerasekara et al, 2020). In the current study, the intensity of reduction was greater in soil monoliths from SSM-treated plots compared with monoliths from LSM-treated and control plots.…”

“…Previous studies investigating flooding‐induced P release have shown a consistent and a substantial increase in pore water and floodwater DRP concentrations with time of flooding in most unamended soils with the exception of a few (Amarawansha et al., 2015; Jayarathne et al., 2016; Kumaragamage et al., 2019). The increase in DRP concentration with flooding and the development of anaerobic conditions have been attributed to pH changes resulting in enhanced solubility of phosphate minerals and the reductive dissolution reactions releasing adsorbed and precipitated P (Maranguit, Guillaume, & Kuzyakov, 2017; Rakotoson, Rabeharisoa, & Smolders, 2016; Weerasekara et al., 2020). In the unamended soil monoliths of the current study, however, a consistent and appreciable increase in DRP concentration was not observed in pore water, possibly due to the diffusion of released P to overlying floodwater (Amarawansha et al., 2015), whereas floodwater DRP concentrations increased by about twofold reaching a peak around 35 DAF and then decreased with further flooding time.…”

Alum reduced phosphorus release from flooded soils under cold spring weather conditions

“…In the unamended treatment, during the period between 7 and 42 DAF, DRP concentrations increased 1.4-4.5-fold in porewater, and 1.8-15.3-fold in floodwater. Although P release from flooded soils is greater under warm than cold temperatures (Kumaragamage et al, 2020;Weerasekara et al, 2021), significant P release into porewater and floodwater was observed in the current study, even when average daily air temperatures were between −5˚C and 5˚C during most of the first 14 days of flooding. Moreover, the peak DRP concentrations in porewater and floodwater did not coincide with the warm/high temperatures observed between 21 and 28 DAF in almost all the soils.…”

“…weather.gc.ca/). These wide temperature fluctuations, which are unlike the simulated conditions used by Weerasekara et al (2021), may result in a severe reduction in soils when flooded, resulting in rapid P release to floodwater; this needs further investigation.…”

“…The amount of P released to floodwater from flooded soils is greater under warm temperatures than under cold temperatures (Dharmakeerthi et al., 2019; Kumaragamage et al., 2020). A recent study reported that P released to overlying floodwater was much less under simulated snowmelt flooding (4 ± 1°C with intermittent freezing) compared to simulated summer flooding (22 ± 1°C) and attributed this to soils not being severely reduced under simulated snowmelt flooding (Weerasekara et al., 2021). However, during actual snowmelt in cold climatic regions such as in the Canadian prairies, the air temperatures can fluctuate widely from as low as −13°C at night to as high as +22°C during the day (https://climate.weather.gc.ca/).…”