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ARS Home » Southeast Area » New Orleans, Louisiana » Southern Regional Research Center » Commodity Utilization Research » Research » Publications at this Location » Publication #317493
Title: Phosphorus concentrations in sequentially fractionated soil samples as affected by digestion methods

Author
item DO NASCIMENTO, CARLOS - Sao Paulo State University (UNESP)
item PAGLIARI, PAULO - University Of Minnesota
item SCHMITT, DJALMA - University Of Santa Catarina
item He, Zhongqi
item Waldrip, Heidi

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2015
Publication Date: 12/9/2015
Citation: Do Nascimento, C.A.C., Pagliari, P.H., Schmitt, D., He, Z., Waldrip, H. 2015. Phosphorus concentrations in sequentially fractionated soil samples as affected by digestion methods. Scientific Reports. 5:17967(13 pages). DOI:10.1038/srep17967.

Interpretive Summary: Sequential fractionation has been used for decades for increasing our understanding on the effects of agricultural practices and management on soil phosphorus (P) pools. Even though, there has been no studies on how laboratory manipulation could affect the level of total P determination in these sequentially extracted fractions. Thus, this study investigated the effect of sample digestion, filtration, and acidification on the total P concentrations determined by inductive coupled plasma-optical emission spectroscopy in four sequentially extracted fractions of 20 soil samples collected in Brazil and the United States. Results indicate that direct inductive coupled plasma-optical emission spectroscopy analysis of undigested extracts is the preferred method to minimize data variability. Therefore, we recommend the direct analysis without extract manipulation for future research with sequential fractionation of soil or other environmental samples.

Technical Abstract: Sequential fractionation has been used for several decades for improving our understanding on the effects of agricultural practices and management on the lability and bioavailability of P in soil, manure, and other soil amendments. Nevertheless, there have been no reports on how manipulation of different fractions prior to ICP-OES analysis affects the total P (TP) concentrations measured. This study investigated effects of sample digestion, filtration, and acidification on the TP concentrations determined by ICP-OES in 20 soils collected in Brazil and the United States. Soils were sequentially extracted with water, 0.5M NaHCO3, 0.1M NaOH, and 1.0M HCl. TP in extracts were either determined without digestion by ICP-OES, or ICP-OES following block digestion, or autoclave digestion. The effects of sample acidification on undigested NaHCO3 and NaOH extracts prior to ICP-OES were also evaluated. Results showed that, TP concentrations measured in block-digested extracts were greater than in autoclave-digested and undigested extracts. In addition, the variability introduced by the block digestion method was much greater than with the other two methods. The effects of filtration were contradictory: in some soil extracts filtration caused a decrease in measured TP and in others there was an increase. Acidification of NaHCO3 extracts resulted in lower measured concentrations of TP, while acidification of NaOH extracts resulted in both increases and decreases in TP. In conclusion, this study showed that ICP-OES of undigested extracts resulted in the lowest variability among the sample preparation methods and should be the preferred method for TP determination in sequentially extracted soil samples.