The phosphorus composition of temperate pasture soils determined by NaOH–EDTA extraction and solution 31 P NMR spectroscopy

Abstract

Information on the composition and dynamics of soil phosphorus (P) remains limited, but is integral to understanding soil biogeochemical cycles. We used solution 31P nuclear magnetic resonance (NMR) spectroscopy to characterise NaOH-EDTA extractable P in 29 permanent pasture soils from England and Wales (total carbon 29-80 g kg-1 soil, clay 219-681 g kg-1 soil, pH 4.4-6.8). Total P ranged between 376 and 1981 mg P kg-1 soil, of which between 45 and 88% was extracted with NaOH-EDTA. The extracts were dominated by orthophosphate monoesters (29-60% extracted P) and inorganic orthophosphate (21-55% extracted P), with smaller concentrations of orthophosphate diesters (2-10% extracted P), pyrophosphate (1-7% extracted P), phosphonates (0-3% extracted P), and traces of polyphosphates. Orthophosphate diesters were subclassified into phospholipids (1-7% extracted P) and DNA (1-6% extracted P). Signals slightly downfield of inorganic orthophosphate were tentatively assigned to aromatic orthophosphate diesters similar in structure to R-(-)-1,1'-binaphthy1-2,2'-diy1 hydrogen phosphate. Such signals are rarely detected in soil extracts, but were present in relatively large concentrations in the samples analysed here (2-5% extracted P). Relationships between functional P groups and soil properties suggested that the various functional groups are involved in the soil P cycle to different extents. In particular, concentrations of orthophosphate monoesters appeared to be controlled by the potential for chemical stabilisation in soil, whereas DNA and pyrophosphate were strongly correlated with the microbial biomass, suggesting an active involvement in biological nutrient turnover.

Quantification of pyrophosphate in soil solution by pyrophosphatase hydrolysis

“…However, the role of pyrophosphate in the nutrition of plants remains poorly understood, due in part to the difficulty in its quantification at low concentrations in soil solution. Ion chromatography was used to assess the fate of pyrophosphate fertilizer added to soils (e.g., McBeath et al, 2007), while pyrophosphate can be quantified in alkaline soil extracts by solution 31 P NMR spectroscopy (e.g., Turner et al, 2003). However, the latter procedure is inappropriate for analysis of soil solution due to its relative insensitivity.…”

Organic matter and pH affect the analysis efficiency of 31 P-NMR

“…Chemical shifts were recorded relative to 85% H 3 PO 4 standard (δ = 0 ppm). Signals were assigned to P species based on data in the literature (Cade-Menun, 2005;Turner et al, 2003b). Peak assignments were made using 31 P-NMR chemical shifts of phosphonate (phon-P: 12 to 23 ppm), orthophosphate (ortho-P: 6 to 7 ppm), orthophosphate monoesters (mono-P: 4 to 6 ppm), phospholipids (lipids-P: 1 to 3 ppm), deoxyribonucleic acid phosphorus (DNA-P: 0 ppm), and pyrophosphate (pyro-P: −3.5 to −4.5 ppm) (Fig.…”

“…The peak areas were calculated by visual inspection and an automated peak analysis tool. From the areas for the different P species, the contribution of each P compound group was calculated relative to TP in the NaOH-EDTA extract, determined by the molybdenum blue method (Cade-Menun, 2005;Turner et al, 2003b).…”

Phosphorus speciation of sediments from lakes of different tropic status in Eastern China

“…Chemical shifts were recorded relative to 85 % H 3 PO 4 standard (δ=0 ppm). Signals were assigned to P compounds based on data reported in the literature (Turner et al 2003b;. Peak assignments were made using 31 P-NMR chemical shifts of phosphonate (phon-P 12 to 23 ppm), orthophosphate (ortho-P 6 to 7 ppm), orthophosphate monoesters (mono-P 4 to 6 ppm), phospholipids (lipids-P 1 to 3 ppm), deoxyribonucleic acid phosphorus (DNA-P 0 ppm), and pyrophosphate (pyro-P −3.5 to −4.5 ppm).…”

“…The peak area responses of samples were calculated by visual inspection and an automated peak analysis tool. Based on the peak area responses for each P species, the contribution of each P compound group was calculated relative to TP in the NaOH-EDTA extraction determined by molybdenum blue method (Shinohara et al 2012;Turner et al 2003b). Lake City Fig.…”