P-chromophore stability of Mehlich-1 and Mehlich-3 under Braga Defelipo or Murphy Riley dosing methods

• Published in: Revista Brasileira de Ciência do Solo Vol. 48
• Main Authors: Denison Queiroz Pogorzelski, Wedisson Oliveira Santos, Gabriel Grossi Pimentel, Fabiane Carvalho Ballotin, Patricia Cardoso Matias, Leonardus Vergütz
• Format: Journal Article
• Language: English
• Published: Sociedade Brasileira de Ciência do Solo 01-01-2024
• Subjects: available-P; colorimetric approach; ring infiltrometer; soil testing
• ISSN: 1806-9657
• DOI: 10.36783/18069657rbcs20230093

ABSTRACT The performance of colorimetric methods for P quantification has been overlooked by researchers for decades. We investigated the performance of two blue colorimetric methods for P quantification, Braga and Defelipo (B&D) and Murphy and Riley (M&R), using two commonly soil P extractants, Mehlich-1 (M1) and Mehlich-3 (M3). Specifically, we evaluated the color development time and its stability in different soil extractant solution proportions (1:1 or 1:4 v/v), the optimum wavelength, limits of detection, and element quantification. Our results indicate that M3 leads to lower limits of detection and quantification for both colorimetric methods, particularly for B&D. For M1, the volumetric ratio (1:1 or 1:4) did not influence color development and both B&D and M&R methods showed a fast color development. However, B&D showed greater color stability (from 5 to 600 min) and an optimum wavelength of 711 nm, while M&R was stable from 27 to 600 min an optimum wavelength of 889 nm. For M3 soil extractant, there are important issues, such as M&R being unstable and B&D presenting slow color development. In addition, the spectral profile obtained from soil extractant was different from the one obtained by the calibration curve without soil for both M&R and B&D. Therefore, the adoption of original methods on P quantification in M3 extracting solution represents a potential source of error, leading to wrong P fertilizer recommendations. Thus, the best option for P quantification in M3 extracts seems to be the use of Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES).