Phosphorus Release from Unamended and Gypsum‐ or Biochar‐Amended Soils under Simulated Snowmelt and Summer Flooding Conditions

• Published in: Journal of environmental quality Vol. 48; no. 4; pp. 822 - 830
• Main Authors: Dharmakeerthi, R. S., Kumaragamage, D., Goltz, D., Indraratne, S. P.
• Format: Journal Article
• Language: English
• Published: The American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc 01.07.2019
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2019.02.0091

Prolonged flooding changes the oxidation–reduction status of soils, often enhancing P release to overlying floodwater. We studied P release from unamended, gypsum‐amended, and biochar‐amended soils under simulated snowmelt flooding (previously frozen, cold flooding at +4°C) and summer flooding (unfrozen, warm flooding at +22°C) using two soils, Fyala clay (FYL‐Cl) and Neuenberg sandy loam (NBG‐SL), from Manitoba, Canada. Amended and unamended soils were packed into vessels and flooded under cold and warm temperatures in the laboratory. Pore water and floodwater samples were taken weekly for 6 wk after flooding (WAF) and thereafter biweekly for 10 WAF and analyzed for dissolved reactive P (DRP), pH, and cation concentrations. The NBG‐SL showed a significantly higher DRP concentration in pore water and floodwater despite its low Olsen P content. Redox potential (Eh) decreased slowly under cold versus warm flooding; hence, redox‐induced P release was substantially lower under cold flooding. Gypsum amendment significantly decreased the floodwater DRP concentrations in NBG‐SL by 38 and 35% under cold and warm flooding, respectively, but had no significant effect in FYL‐Cl, which had low DRP concentrations (<1.2 mg L−1) throughout the flooding period. Biochar amendment significantly increased floodwater DRP concentrations by 27 to 68% in FYL‐Cl under cold and warm flooding, respectively, but had no significant effect in NBG‐SL. The results indicate substantially less P release under cold than under warm flooding. Gypsum was effective in reducing floodwater DRP concentrations only at high DRP concentrations; thus, the effectiveness was greater under warm than under cold flooding conditions. Core Ideas Floodwater DRP concentration increased with time of flooding in amended and unamended soils. Increase in floodwater DRP concentration was less under simulated snowmelt than summer flooding. Rate of P diffusion from pore water to floodwater was less under simulated snowmelt flooding. Gypsum reduced floodwater DRP in one soil with DRP concentrations >1 mg L−1, but not in the other. Woodchip biochar was ineffective in reducing P release from soils to overlying floodwater.