Validation of the near infrared spectroscopy method for determining soil organic carbon by employing a proficiency assay for fertility laboratories

Current research indicates that near infrared (NIR) spectroscopy is the most promising alternative technique for the determination of soil organic carbon (SOC) in laboratories worldwide and that it may serve as a total or partial replacement for the traditional wet chemistry-methods. In this research, NIR spectroscopy was developed and validated as a method for the determination of SOC aiming to promote the use of NIR technology in the soil laboratories of Brazil as a routine analysis method. To this end, multivariate calibration models were constructed from a large number of soil samples (1490 samples) that encompassed the variability of Brazilian soils. These models were validated by submitting the concentrations of soil organic matter (SOM) as determined by NIR spectroscopy to the proficiency assay for fertility laboratories, which is coordinated by the Brazilian Agricultural Research Corporation (Embrapa Soils). The proposed methodology using NIR spectroscopy received the excellence index of quality, which gives a certificate seal issued by the interlaboratory programme. Therefore, the robustness of the NIR method was proved in a conclusive way by a proficiency test programme dedicated to evaluating the reference method for SOM determination employed by over a hundred soil laboratories in Brazil.