A rapid ammonium fluoride method to determine the oxygen isotope ratio of available phosphorus in tropical soils

Abstract

Rationale The isotopic composition of oxygen bound to phosphorus (δ18OP value) offers an opportunity to gain insight into P cycling mechanisms. However, there is little information for tropical forest soils, which presents a challenge for δ18OP measurements due to low available P concentrations. Here we report the use of a rapid ammonium fluoride extraction method (Bray‐1) as an alternative to the widely used anion‐exchange membrane (AEM) method for quantification of δ18OP values of available P in tropical forest soils. Methods We compared P concentrations and δ18OP values of available and microbial P determined by AEM and Bray‐1 extraction for a series of tropical forest soils from Panama spanning a steep P gradient. This involved an assessment of the influence of extraction conditions, including temperature, extraction time, fumigation time and solution‐to‐soil ratio, on P concentrations and isotope ratios. Results Depending on the extraction conditions, Bray‐1 P concentrations ranged from 0.2 to 66.3 mg P kg−1 across the soils. Extraction time and temperature had only minor effects on Bray‐1 P, but concentrations increased markedly as the solution‐to‐soil ratio increased. In contrast, extraction conditions did not affect Bray‐1 δ18OP values, indicating that Bray‐1 provides a robust measure of the isotopic composition of available soil P. For a relatively high P soil, available and fumigation‐released (microbial) δ18OP values determined by Bray‐1 extraction (20‰ and 16‰, respectively) were higher than those determined by the AEM method (18‰ and 12‰, respectively), which we attribute to slightly different P pools extracted by the two methods and/or differences resulting from the longer extraction time needed for the AEM method. Conclusions The short extraction time, insensitivity to extraction conditions and smaller mass of soil required to extract sufficient P for isotopic analysis make Bray‐1extraction a suitable alternative to the AEM method for the determination of δ18OP values of available P in tropical soils.

Dynamics of Soil Nutrients, Microbial Community Structure, Enzymatic Activity, and Their Relationships along a Chronosequence of Pinus massoniana Plantations

“…Nitrate nitrogen (NO 3 --N) was determined by ultraviolet spectrophotometry [34]. Available phosphorus (AP) was extracted by NH 4 F, followed by the colorimetric method [35]. The pH value of soil was determined by the glass composite electrode method (water soil ratio of 2.5: 1) [20].…”

Cost-Effective Modern Chemical Sensor System for Soil Macronutrient Analysis Applied to Thai Sustainable and Precision Agriculture

“…In the standard method for nitrate, soil samples were extracted by potassium chloride according to ISO 14256 [ 20 ]. Ammonium fluoride in the acidic medium and ammonium acetate of pH 7 were used for the extraction of the available phosphorus and potassium ions, respectively [ 21 , 22 ]. The soil extracts were detected via the spectrophotometric method for nitrate and available phosphorus [ 7 , 16 ].…”

Quantification of Cl, Br and I in Geological Materials by NH4F Digestion: Comparison with Rapid Acid Digestion

“…239.5 °C), the higher boiling point (260 °C) of NH 4 F allows an elevated digestion temperature (250 °C) to effectively decompose refractory minerals in 1-1.5 h, which is approximately twelve times faster than traditional high pressure closed-vessel acid digestion (Hu et al 2013). Efficient and simplified NH 4 F digestion techniques have been developed for multielement and oxygen isotope ratio measurement in various rocks and soils (Hu et al 2010, Pfahler et al 2020.…”

“…2010, 2013, Pfahler et al . 2020). During the high temperature digestion procedure, thermal decomposition of NH 4 F can produce ammonia gas and NH 4 HF 2 which implies that the efficiency of avoiding the loss of halogens using NH 4 F as the digestion reagent is improved compared with NH 4 HF 2 digestion, because more NH 3 is released from the decomposition of NH 4 F. Therefore, NH 4 F digestion can also be treated as an excellent candidate method for the determination of halogens in geological materials.…”