Dep. of Environmental Studies and Sciences, The Univ. of Winnipeg, Winnipeg, MB, R3B 2E9, Canada.
Dep. of Soil Science, Faculty of Agriculture, Univ. of Peradeniya, Peradeniya, 20400, Sri Lanka.
J Environ Qual. 2022 Jan;51(1):90-100. doi: 10.1002/jeq2.20319. Epub 2022 Jan 22.
Anaerobic conditions developed during flooding can increase phosphorus (P) losses from soils to waterways. Soil amendment with gypsum (CaSO ·2H O) can effectively reduce flooding-induced P release, but its effectiveness is soil dependent, and the reasons are poorly understood. The objectives of this study were to reveal the possible inorganic P transformations during flooding of two soils (acidic-Neuenberg sandy loam [NBG-SL] and alkaline-Fyala clay [FYL-Cl]), with and without gypsum amendment prior to flooding. Porewater samples collected at 0, 35, and 70 d after flooding (DAF) from soils incubated in vessels were analyzed for dissolved reactive P (DRP); pH; and concentrations of calcium (Ca), magnesium, iron (Fe), manganese, chloride, nitrate, sulfate, and fluoride. Thermodynamic modeling using Visual MINTEQ software and chemical fractionation of soil P were used to infer P transformations. Soil redox potential (Eh) decreased with flooding and favored reductive dissolution of Fe-associated P increasing porewater DRP concentrations. Greater solubility of Ca-P under acidic pH maintained a higher DRP concentration in NBG-SL during early stages of flooding. A subsequent increase in pH with flooding and higher Ca concentration with added gypsum enhanced the stability of Ca-P (β-tricalcium phosphate and octacalcium phosphate), reducing the DRP concentration in gypsum-amended NBG-SL. Stability of Ca-P was less affected with flooding and gypsum amendment in FYL-Cl soil because it had an alkaline pH and inherently higher Ca concentration. The FYL-Cl, with a more rapid decrease in Eh than NBG-SL, became severely reduced, releasing more P and Fe by 70 DAF. These conditions favored vivianite formation in FYL-Cl but not in NBG-SL.
在洪水期间形成的厌氧条件会增加土壤中磷（P）向水道的流失。用石膏（CaSO·2H2O）对土壤进行改良可以有效地减少洪水引发的 P 释放，但这种效果取决于土壤，其原因尚不清楚。本研究的目的是揭示在没有和有石膏改良的情况下，两种土壤（酸性-Neuenberg 砂壤土[NBG-SL]和碱性-Fyala 粘壤土[FYL-Cl]）在洪水期间可能发生的无机 P 转化。在容器中培养的土壤在洪水后 0、35 和 70 天（DAF）采集的孔隙水样品用于分析溶解反应性 P（DRP）；pH；以及钙（Ca）、镁、铁（Fe）、锰、氯、硝酸盐、硫酸盐和氟化物的浓度。使用 Visual MINTEQ 软件进行热力学建模和土壤 P 的化学分馏用于推断 P 转化。土壤氧化还原电位（Eh）随洪水而降低，有利于铁相关 P 的还原溶解，增加孔隙水 DRP 浓度。在酸性 pH 下，Ca-P 的更大溶解度在 NBG-SL 洪水初期保持较高的 DRP 浓度。随后随着洪水和添加石膏的 Ca 浓度增加，Ca-P（β-磷酸三钙和八钙磷酸盐）的稳定性增强，降低了添加石膏的 NBG-SL 中 DRP 的浓度。在 FYL-Cl 土壤中，由于其碱性 pH 和固有的较高 Ca 浓度，洪水和石膏改良对 Ca-P 的稳定性影响较小。与 NBG-SL 相比，Eh 下降更快的 FYL-Cl 变得严重还原，在 70 DAF 时释放出更多的 P 和 Fe。这些条件有利于在 FYL-Cl 中形成磷铁矿，但在 NBG-SL 中则不然。
