Determination of Low Concentrations of Phosphorus in Soil Extracts Using Malachite Green

Abstract

A sensitive method is needed to analyze soil‐water extracts that contain P at submicromolar concentrations. The proposed spectrophotometric method, based on the ionic association of malachite green with phosphomolybdate under acidic conditions, was evaluated on soil extracts. The molar absorptivity was 64641 ± 743 L mol−1 cm−1. Absorbance of the reagent blank was 0.069 ± 0.004. With 1‐cm path length cells and limiting absorbance of 0.004, the detection limit calculated from the Beer‐Lambert equation was 6.7 × 10−8 M orthophosphate P. Recovery of added P in saturated paste extracts averaged 91% with a range of 87 to 94% and averaged 101% with a range of 93 to 109% for 1:1 soil/water extract. The method was successfully applied to saturated paste extracts from soils of varied organic matter content and pH. The proposed malachite green method allows for P determination in restricted volume samples and at concentrations too low for the standard Murphy‐Riley method.

Relationships of phosphorus fractions to organic carbon content in surface soils in mature subtropical forests, Dinghushan, China

“…Inorganic P concentration in the 1.0 M NH 4 Cl extract (soluble Pi) was below the detection limit by the molybdate blue method, and therefore reanalysed using the malachite green method (Ohno and Zibilske 1991). Organic P in the 0.1 M NH 4 F (Al-Po) and 0.1 M NaOH (Fe-Po) extracts was calculated as the difference between total P determined after persulfate digestion (Ormaza-González and Statham 1996) and inorganic P. Residual organic P (residual Po) was calculated as the difference of inorganic P between the H 2 SO 4 II and III extracts.…”

Nitrogen and phosphorus availability at early stages of soil development in the Damma glacier forefield, Switzerland; implications for establishment of N2-fixing plants

“…Each digested sample was transferred into a volumetric flask, diluted to 25 ml with distilled water and homogenized by mixing (Welc et al 2014). Extracts were filtered through 0.20 μm filters (Santorius), and total P was measured colorimetrically at λ = 610 nm (UV 1601 Spectrophotometer, Shimadzu) using malachite green (Fluka AG, Switzerland) as a colour agent (Ohno and Zibilske 1991).…”

The oxygen isotope composition of phosphate released from phytic acid by the activity of wheat and <i>Aspergillus niger</i> phytase

“…Directly after the addition of the reagents, the tubes were closed and only opened for sampling. The concentration of released P i in the assays was monitored using the colorimetric malachite green method (Ohno and Zibilske, 1991). After 48 h, P i yield was usually close to 65 % and did not change any more, despite the enzyme being still active, which indicates that the original substrate IP 6 molecule was degraded to myo-inositol biphosphate (IP 2 ) and four P i molecules (4 × P i /6 × P i = 66.6 %).…”