Determination of Carbon, Nitrogen and Sulfur in Soil

Importance of the Topic

Carbon, nitrogen and sulfur are key macronutrients that govern soil fertility and plant development. Carbon content reflects soil organic matter and relates to nutrient availability, while nitrogen and sulfur are essential for protein and enzyme formation. Accurate measurement of these elements enables optimized fertilization strategies and supports sustainable agricultural practices.

Objectives and Study Overview

This application note evaluates the performance of the LECO CNS928 macro combustion determinator for simultaneous quantification of carbon, nitrogen and sulfur in soil samples. The study aims to demonstrate method precision, assess calibration protocols, and compare analytical outcomes using different carrier gases and aliquot loop configurations.

Instrumentation Used

The LECO CNS928 employs a pure oxygen, high‐temperature (1450 °C) horizontal ceramic furnace for macro sample combustion. Resulting gases are collected in a ballast and introduced via inert carrier gas (helium or argon) into non‐dispersive infrared detectors for CO2 and SO2, and a thermal conductivity detector for N2. The instrument supports two gas aliquot loop sizes (3 cm3 and 10 cm3) to accommodate various concentration ranges and optimize reagent consumption.

Methodology

Sample Preparation

• Dry soil samples at 105 °C for one hour; store in a desiccator and analyze within 24 h.
• Grind to a uniform consistency and weigh approximately 0.25 g into pre‐baked ceramic boats.

Analysis Procedure

• Condition the system with blank replicates until baseline stability and precision criteria are met.
• Calibrate with certified reference materials: BBOT for nitrogen and sulfur, calcium carbonate and synthetic carbons for carbon.
• Add ~1 g of COM-CAT catalyst to each sample, mix thoroughly, and load into the autoloader.
• Select carrier gas, loop size, and method parameters, then initiate the analysis sequence.

Main Results and Discussion

Replicate analyses of certified soil materials yielded relative standard deviations below 1.0 % for carbon and below 2.0 % for nitrogen and sulfur. Both 3 cm3 and 10 cm3 loops produced comparable accuracy, with the smaller loop extending catalyst life and reducing cost per analysis. Helium provided higher sensitivity, while argon offered a cost-effective alternative with slightly lower precision.

Benefits and Practical Applications

The CNS928 delivers rapid, reliable multi‐element analysis for soil fertility assessment, supporting agricultural decision‐making, research laboratories and QA/QC operations. Its versatile configuration accommodates a wide concentration range and balances operational efficiency with reagent and carrier gas consumption.

Future Trends and Potential Applications

Emerging developments may include automated sample handling, integration with moisture measurement modules, and exploration of novel, eco‐friendly carrier gases. Application of the method to environmental monitoring, waste characterization and organic amendment analysis represents further growth opportunities.

Conclusion

The LECO CNS928 macro combustion determinator offers a robust and flexible solution for simultaneous determination of carbon, nitrogen and sulfur in soils. Its high precision, efficient workflow and adaptability to different analytical conditions make it a valuable tool for soil analysis and agronomic management.

References

LECO Corporation. Determination of Carbon, Nitrogen and Sulfur in Soil. Application Note, Form No. 203-821-600, Rev 1, April 2020. LECO Corporation, Saint Joseph MI USA.