The lack of matrix-matched certified reference materials (CRMs) for sandy agricultural soils in semi-arid regions represents a major limitation for ensuring analytical accuracy and interlaboratory comparability. This study aimed to develop and certify a soil CRM representative of intensively cultivated sandy soils from the Souss-Massa region (Morocco). A composite soil sample exceeding 450 kg was collected from the 0–30 cm layer using a multi-point sampling strategy, then air-dried, sieved through a 2 mm mesh, homogenized, and bottled into 600 units in accordance with ISO 17034:2016 and ISO 33405:2024. Homogeneity was evaluated using one-way ANOVA, with F_calculated values ranging from 0.29 to 1.38, all below the critical value (F_critical = 2.39), confirming the absence of significant between-bottle variability. The relative between-bottle standard uncertainty (u_bb) ranged from 0.09 to 2.09 %, depending on the parameter. Short-term stability (24 days at 50 °C) and long-term stability (24 months at ambient temperature) were evaluated using linear regression, and no significant trends were observed (p > 0.05). The corresponding relative stability uncertainties ranged from 0.19 to 3.45 % for short-term stability (u_sts) and from 0.33 to 4.37 % for long-term stability (u_lts). Certified values were assigned through an interlaboratory comparison involving eight ISO/IEC 17025:2017-accredited laboratories using robust statistical methods in accordance with ISO 33405:2024. The assigned values properties include particle-size distribution (sand: 81.5 ± 3.3 %, silt: 9.8 ± 1.0 %, and clay: 9.7 ± 0.9 %), pH (6.06 ± 0.05), electrical conductivity (0.410 ± 0.024 mS cm⁻1), organic carbon (10.2 ± 0.7 g kg⁻1), total nitrogen (1.14 ± 0.06 g kg⁻1), available phosphorus (Olsen-extractable P: 71 ± 7 mg kg⁻1), and exchangeable potassium (K⁺: 693 ± 34 mg kg⁻1; 0.177 cmol( +) kg⁻1). All assigned values are accompanied by expanded uncertainties (k = 2), with relative expanded uncertainties below 10.2%. AG-SOIL-23 constitutes a region-specific CRM suitable for method validation, quality control, and interlaboratory harmonization in laboratories analyzing sandy agricultural soils under semi-arid conditions.

Production and certification of AG-SOIL-23: a sandy agricultural soil certified reference material from the Souss-Massa region (Morocco)

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发表日期：

2026年7月28日

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Aziz Soulaimani,
Mohamed El Gharous,
Khalil El Mejahed,
Haitam Moulay,
Latifa Hajji,
Said Gmouh

摘要

The lack of matrix-matched certified reference materials (CRMs) for sandy agricultural soils in semi-arid regions represents a major limitation for ensuring analytical accuracy and interlaboratory comparability. This study aimed to develop and certify a soil CRM representative of intensively cultivated sandy soils from the Souss-Massa region (Morocco). A composite soil sample exceeding 450 kg was collected from the 0–30 cm layer using a multi-point sampling strategy, then air-dried, sieved through a 2 mm mesh, homogenized, and bottled into 600 units in accordance with ISO 17034:2016 and ISO 33405:2024. Homogeneity was evaluated using one-way ANOVA, with F_calculated values ranging from 0.29 to 1.38, all below the critical value (F_critical = 2.39), confirming the absence of significant between-bottle variability. The relative between-bottle standard uncertainty (u_bb) ranged from 0.09 to 2.09 %, depending on the parameter. Short-term stability (24 days at 50 °C) and long-term stability (24 months at ambient temperature) were evaluated using linear regression, and no significant trends were observed (p > 0.05). The corresponding relative stability uncertainties ranged from 0.19 to 3.45 % for short-term stability (u_sts) and from 0.33 to 4.37 % for long-term stability (u_lts). Certified values were assigned through an interlaboratory comparison involving eight ISO/IEC 17025:2017-accredited laboratories using robust statistical methods in accordance with ISO 33405:2024. The assigned values properties include particle-size distribution (sand: 81.5 ± 3.3 %, silt: 9.8 ± 1.0 %, and clay: 9.7 ± 0.9 %), pH (6.06 ± 0.05), electrical conductivity (0.410 ± 0.024 mS cm^⁻1), organic carbon (10.2 ± 0.7 g kg^⁻1), total nitrogen (1.14 ± 0.06 g kg^⁻1), available phosphorus (Olsen-extractable P: 71 ± 7 mg kg^⁻1), and exchangeable potassium (K⁺: 693 ± 34 mg kg^⁻1; 0.177 cmol( +) kg^⁻1). All assigned values are accompanied by expanded uncertainties (k = 2), with relative expanded uncertainties below 10.2%. AG-SOIL-23 constitutes a region-specific CRM suitable for method validation, quality control, and interlaboratory harmonization in laboratories analyzing sandy agricultural soils under semi-arid conditions.