Speciation and distribution of P associated with Fe and Al oxides in aggregate-sized fraction of an arable soil

Abstract

Abstract. To maximize crop productivity fertilizer P is generally applied to arable soils, a significant proportion of which becomes stabilized by mineral components and in part subsequently becomes unavailable to plants. However, little is known about the relative contributions of the different organic and inorganic P bound to Fe/Al oxides in the smaller soil particles. Alkaline (NaOH-Na 2 EDTA) extraction with solution 31 P-nuclear magnetic resonance ( 31 P-NMR) spectroscopy is considered a reliable method for extracting and quantifying organic P and (some) inorganic P. However, any so-called residual P after the alkaline extraction has remained unidentified. Therefore, in the present study, the amorphous (a) and crystalline (c) Fe/Al oxide minerals and related P in soil aggregate-sized fractions (> 20, 2-20, 0.45-2 and < 0.45 µm) were specifically extracted by oxalate (a-Fe/Al oxides) and dithionite-citrate-bicarbonate (DCB, both a-and c-Fe/Al oxides). These soil aggregate-sized fractions with and without the oxalate and DCB pre-treatments were then sequentially extracted by alkaline extraction prior to solution 31 P-NMR spectroscopy. This was done to quantify the P associated with a-and c-Fe/Al oxides in both alkaline extraction and the residual P of different soil aggregate-sized fractions.The results showed that overall P contents increased with decreasing size of the soil aggregate-sized fractions. However, the relative distribution and speciation of varying P forms were found to be independent of soil aggregate-size. The majority of alkaline-extractable P was in the a-Fe/Al oxide fraction (42-47 % of total P), most of which was orthophosphate (36-41 % of total P). Furthermore, still significant amounts of particularly monoester P were bound to these oxides. Intriguingly, however, Fe/Al oxides were not the main bonding sites for pyrophosphate. Residual P contained similar amounts of total P associated with both a-(11-15 % of total P) and c-Fe oxides (7-13 % of total P) in various aggregate-sized fractions, suggesting that it was likely occluded within the a-and c-Fe oxides in soil. This implies that, with the dissolution of Fe oxides, this P may be released and thus available for plants and microbial communities.

Assessment of phosphorus status influenced by Al and Fe compounds in volcanic grassland soils

“…Nevertheless, Fe ox did not correlate with labile P i (NaHCO 3 -P i and NaOH-P i ; Table 6). The relationship between Fe ox and residual P has been previously reported by Jiang et al (2015); they found that the majority of P in the residual fraction was occluded within Fe oxides, which implies that this P may be re- et al (2016). In this sense, our previous research indicates that aggregates of allophane in Piedras Negras can retain 12% of C against intensive peroxide treatment (Calabi-Floody et al, 2012).…”

Visualization of Colloid Transport Pathways in Mineral Soils Using Titanium(IV) Oxide as a Tracer

“…The particle-facilitated transport has been identified as important pathway for the leaching of contaminants like pesticides, heavy metals, and phosphorous (P) (Jacobsen et al, 1997;de Jonge et al, 2004;Makris et al, 2006). Jiang et al (2015) investigated the P contents of soil aggregate-sized fractions from <0.45 to >20 mm and found a significant increase of the overall P content with decreasing aggregate-sized fractions. Heathwaite et al (2005) stated that total and reactive P is favorably transported in fractions of 2 mm, or smaller than 0.001 mm.…”

Characterizing phosphorus forms in cropland soils with solution 31P-NMR: past studies and future research needs

“…In Europe, two studies from Germany and Denmark used the same research plots [20,21], but both used dialysis and identified only broad peaks. There was a more recent study from Germany [58], one each from Finland, Sweden and Switzerland [59][60][61]; one specifically from England [62] and one from the United Kingdom in general [10]. The study from Israel is included here too [63].…”

“…The study from Israel is included here too [63]. Three of these studies identified only broad compound classes [10,58,59], one identified the majority of peaks [60] and three identified peaks in detail [61][62][63]. In North America, there was one study from Mexico [22], five from Canada [23,32,33,64,65] and five from the USA [31,[66][67][68][69].…”