Crystallization of single and binary iron‐ and aluminum hydroxides affect phosphorus desorption

Abstract

In acidic soils, phosphorus availability is affected by its strong affinity for mineral surfaces, especially Fe‐ and Al‐hydroxides. Plant roots have developed adaptive strategies to enhance the availability of phosphorus, including producing and exuding low molecular weight organic acids with a high affinity for phosphorus that competes with high molecular weight organic ligands formed during humification and mineralization. The aim of this study was to characterize the kinetics and mechanism of phosphorus desorption from Fe‐ and Al‐hydroxides of variable crystallinity, as well as binary Fe:Al‐hydroxide mixtures. Long‐term desorption experiments (56 days) were conducted with CaCl2, CaSO4, citric acid, and humic acid as competitive sorptives. CaCl2 and CaSO4 were selected as general inorganic sorptives and citric and humic acids were selected as organic ligands produced by organisms in the rhizosphere or following humification. The cumulative phosphorus desorption increased following the order CaCl2 < CaSO4 < humic acid < citric acid. Amorphous ferrihydrite and Fe‐rich Fe:Al‐hydroxides exhibited much less desorption when exposed to inorganic solutions than the crystalline and Al‐rich Fe:Al‐hydroxide mixtures. Models of the desorption data suggest phosphorus desorption with citric acid is diffusion‐controlled for ferrihydrite and Fe‐rich amorphous Fe:Al‐hydroxides. When humic acid was the sorptive, metal‐organic complexes accumulated in the solution. The results suggest organic compounds, especially citric acid, are more important for liberating phosphorus from Fe‐ and Al‐minerals than inorganic ions present in the soil solution.

Kinetics of Phosphorus Release from Vivianite, Hydroxyapatite, and Bone Char Influenced by Organic and Inorganic Compounds

“…The mobilization of these P resources can take place by different processes, while the cumulative P release using CA was clearly higher than with CaCl 2 . It is well known that the exchange with inorganic ions plays an inferior role compared to organic components [37][38][39]. Inorganic reaction solutions such as CaCl 2 contribute to the mobilization of P from nonspecific adsorbed P from low-affinity sites, while structural bound or specific adsorbed P from high-affinity sites can hardly be affected due to the strong bonds [2,40,41].…”

“…This means that in addition to the readily available P pools, soil reserves can be used in the long-term, hence, reducing agricultural runoff and eutrophication of natural waters. Depending on the crystallization grade and the Fe/Al-ratio, the P mobilization capacity of these hydroxides can be increased up to 49% by using CA [39]. In particular, the comparison of the efficiency and kinetics of P release from VI and BC showed that VI, despite the influence of CA, had less available P in both the short-and long-term, which can cause an increase in the less available P pool.…”

Investigation of the soil properties that affect Olsen P critical values in different soil types and impact on P fertiliser recommendations

“…The untreated soil Olsen-P (c) was positively influenced by TP and CAlox prior to P addition, and negatively influenced by A/CMnox, suggesting that the Olsen extraction method can more efficiently extract P from CAlox than A/CMnox (Braun et al, 2019). It has been shown that phosphate binding to C/AAlox consists mainly of surface complexes that are readily extracted by weak extraction solutions (Gypser, Hirsch, Schleicher, & Freese, 2018;Gypser, Schutze, & Freese, 2019). However, it is not clear how phosphate is adsorbed to Mnox, as although some authors suggest binding to MnO 2 is by outer-sphere surface complexes (Mustafa, Zaman, & Khan, 2006), it has been suggested that binding to hydrous manganese oxide may be by stronger inner sphere complexes (Pan et al, 2014).…”

Deciphering competitive interactions: Phosphate and organic matter binding on goethite through experimental and theoretical insights

“…In contrast, Borggaard et al (2005) reported a limited effect on P adsorption at aluminum oxide, ferrihydrite, and goethite upon covering the surfaces with soil-derived OM. In a recent long-term desorption study by Gypser et al (2019), utilizing competitive inorganic and organic anions to release adsorbed P from Fe-and Al-hydroxides, it was found that P desorption increased in the order CaCl2 < CaSO4 < humic acid < citric acid. A further desorption study by Gypser et al (2021) showed that goethite exhibited the highest desorption, followed by gibbsite and then ferrihydrite upon applying both organic and inorganic competitors.…”