Phosphorus Concentrations in Sequentially Fractionated Soil Samples as Affected by Digestion Methods

Abstract

Sequential fractionation has helped improving our understanding of the lability and bioavailability of P in soil. Nevertheless, there have been no reports on how manipulation of the different fractions prior to analyses affects the total P (TP) concentrations measured. This study investigated the effects of sample digestion, filtration, and acidification on the TP concentrations determined by ICP-OES in 20 soil samples. Total P in extracts were either determined without digestion by ICP-OES, or ICP-OES following block digestion, or autoclave digestion. The effects of sample filtration, and acidification on undigested alkaline extracts prior to ICP-OES were also evaluated. Results showed that, TP concentrations were greatest in the block-digested extracts, though the variability introduced by the block-digestion was the highest. Acidification of NaHCO3 extracts resulted in lower TP concentrations, while acidification of NaOH randomly increased or decreased TP concentrations. The precision observed with ICP-OES of undigested extracts suggests this should be the preferred method for TP determination in sequentially extracted samples. Thus, observations reported in this work would be helpful in appropriate sample handling for P determination, thereby improving the precision of P determination. The results are also useful for literature data comparison and discussion when there are differences in sample treatments.

Role of Organic Anions and Phosphatase Enzymes in Phosphorus Acquisition in the Rhizospheres of Legumes and Grasses Grown in a Low Phosphorus Pasture Soil

“…Inorganic P (Pi) in the alkali extracts (NaHCO 3 -Pi, NaOH1-Pi, NaOH2-Pi) was determined according to Dick and Tabatabai [ 126 ] and He and Honeycut [ 127 ] to avoid overestimation of inorganic P due to mineralization of labile organic P. The method of Murphy and Riley [ 119 ] was used to determine Pi in the acid extracts (NH 4 Cl-Pi, HCl-Pi, and residual Pi). Total P (Pt) in the alkali extracts was measured using ICP-EOS according to do Nascimento et al [ 128 ], while organic P (Po) was calculated as the difference between Pt and Pi in each fraction. The total soil P was calculated as the sum of all nine fractions.…”

The Contrasting Effects of Alum‐Treated Chicken Manures and KH2PO4 on Phosphorus Behavior in Soils

“…The difference between TP and RP in these Mehlich‐3 extracts was NRP, which is considered here to be organic P. Digestion with alkaline persulfate was unsuccessful for these Mehlich‐3 extracts, likely due to the strong pH buffer capacity of Mehlich‐3 solution. do Nascimento et al (2015) reported that soil TP determined by inductively coupled plasma optical emission spectroscopy (ICP‐OES) may be overestimated after block digestion. Thus, we acknowledge that manipulation during digestion could introduce more variability to the final results.…”

Forms and Lability of Phosphorus in Algae and Aquatic Macrophytes Characterized by Solution 31P NMR Coupled with Enzymatic Hydrolysis

“…Molybdate-reactive P (i. e. MRP) was measured by the molybdenum blue/ascorbic acid method4041. The TP concentration of extracts was determined after digestion with potassium persulfate (K 2 S 2 O 8 ) in an autoclave at 121 °C for 30 min42. Concentrations of P o in extracts were then calculated as the difference between concentrations of TP and MRP.…”