Metrological Foundations for Soil Analysis: A Global Review of Certified Reference Materials for Agricultural Laboratories

Abstract

Certified Reference Materials (CRMs) constitute the metrological foundation for reliable and comparable soil measurements in agricultural laboratories worldwide. They provide SI-traceable benchmarks for instrument calibration, method validation, and quality control in the determination of key agronomic parameters, including texture, pH, electrical conductivity, organic carbon, macro- and micronutrients, and potentially toxic elements.

This review critically examines the international metrological framework governing soil CRMs, with emphasis on ISO/IEC 17025, ISO 17034, and the emerging ISO 33400 series (notably ISO 33405 and ISO 33401), which collectively define requirements for sampling, pretreatment, homogenization, homogeneity and stability assessment, characterization, value assignment, and uncertainty evaluation. It summarises global advances in CRM production and evaluates the current availability of soil matrix CRMs from major producers such as NIST, BAM, LGC, and the JRC.

Despite a growing market, the portfolio of soil CRMs remains limited relative to the diversity of pedological and agro-climatic conditions. High acquisition costs, logistical constraints, and limited regional production capacity particularly constrain laboratories in emerging economies, hindering method validation, proficiency testing, accreditation, and interlaboratory comparability.

The review identifies critical gaps in matrix-specific soil CRMs that should be addressed as a priority and outlines the investment, infrastructure development, and international collaboration required to strengthen regional production capabilities and metrological traceability chains. Addressing these gaps is essential to enhance measurement confidence, support ISO/IEC 17025 accreditation, and underpin evidence-based agricultural management, food security, and environmental regulation.