Determination of Moisture in Soil

Significance of the Topic

Soil moisture is a key parameter in agricultural and environmental sciences affecting nutrient availability, crop yield, soil temperature regulation, microbial activity and groundwater dynamics. Accurate moisture measurement also enables proper correction of soil analytical results for constituents such as carbon, nitrogen and sulfur.

Objectives and Study Overview

This note demonstrates a thermogravimetric approach to determine moisture content in soil using LECO TGM800 and TGA801 analyzers. The objectives include establishing a robust loss-on-drying protocol, optimizing method parameters and evaluating precision across certified reference materials.

Methodology

• Technique: Loss-on-drying by thermogravimetric analysis, tracking mass change from 25 C to 110 C.
• Sample: Uniform soil samples of approximately 1.0 g loaded into aluminum foil crucibles (TGM800) or ceramic crucibles (TGA801).
• Parameters: Ramp rate of 20 C per minute (TGM800) or 10 C per minute (TGA801), hold at 110 C for 60 minutes, air atmosphere with flow rates of 5 L per minute and 10 L per minute respectively, final mass determined at constancy criteria.
• Standard: Based on ASTM D2974-13 for moisture determination in organic soils.

Used Instrumentation

• LECO TGM800 macro thermogravimetric analyzer (16-sample carousel)
• LECO TGA801 macro thermogravimetric analyzer (19-sample carousel)
• Accessories: Aluminum foil crucibles, ceramic crucibles and double-sided spoons.

Main Results and Discussion

Precision was evaluated using three certified soil reference materials:

• Reference material 502-694: Average moisture 6.03 plus or minus 0.05 % (TGM800) and 5.88 plus or minus 0.03 % (TGA801).
• Reference material 502-814: Average moisture 9.63 plus or minus 0.01 % (TGM800) and 9.45 plus or minus 0.01 % (TGA801).
• Reference material 502-962: Average moisture 2.55 plus or minus 0.03 % (TGM800) and 2.61 plus or minus 0.02 % (TGA801).

These results demonstrate high repeatability and consistency between instruments. Slight differences reflect instrument-specific ramp rates and atmosphere control.

Benefits and Practical Applications

• Rapid and reliable moisture quantification supports informed irrigation management and crop optimization.
• High sample throughput (up to 19 samples per run) enables efficient laboratory workflows.
• Accurate moisture correction improves downstream soil constituent analyses such as carbon and nitrogen determination.

Future Trends and Opportunities

Integration of automated sample handling, real-time moisture monitoring networks and coupling with spectroscopic or chromatographic techniques may further enhance soil analysis capabilities. Development of portable thermogravimetric systems could enable field-deployable moisture assessment.

Conclusion

The described thermogravimetric loss-on-drying method provides a robust, reproducible and high-throughput solution for soil moisture determination. Its adoption can improve data quality in research, quality control and agricultural practice.

Reference

• ASTM D2974-13 Standard Test Methods for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils