Soil analysis with NIR spectroscopy

Importance of the Topic

Soil properties such as organic matter content, nutrient availability and texture directly influence crop productivity, environmental sustainability and land management decisions.
Rapid, accurate assessment methods enable better fertilization strategies, soil health monitoring and resource optimization in agriculture and environmental science.

Objectives and Study Overview

This application note demonstrates a near-infrared spectroscopy approach for simultaneous, multi-parameter soil analysis in a few seconds.
Key targets include organic matter, pH, texture fractions (sand, silt, clay), exchangeable calcium and magnesium, and limestone content.

Methodology

Air-dried soil samples were measured in reflection mode over the 1000–2250 nm range.
Each sample was rotated in a large cup accessory while spectra were averaged to compensate for heterogeneity.
Calibration models were developed using dedicated software and validated against standard reference methods.

Used Instrumentation

• Metrohm NIR Analyzer configured for 1000–2250 nm reflection measurements
• Large cup sample accessory with rotation capability
• Metrohm software suite for data acquisition, spectral preprocessing and model development

Main Results and Discussion

Prediction models exhibited strong agreement with conventional reference methods across all parameters:

• Organic matter: R2 0.994, SEP 0.87 %
• pH: R2 0.887, SEP 0.29
• Limestone: R2 0.843, SEP 1.11 %
• Clay: R2 0.724, SEP 7.58 %
• Silt: R2 0.663, SEP 5.20 %
• Sand: R2 0.732, SEP 7.64 %
• Exchangeable Ca: R2 0.783, SEP 2.36 ‰
• Exchangeable Mg: R2 0.804, SEP 0.63 ‰

These results confirm that NIR spectroscopy can deliver reliable, multi-parameter soil analyses in seconds, suitable for routine laboratory screening.

Benefits and Practical Applications

• Analysis time reduced to seconds per sample
• No chemical reagents or solvents required
• Minimal sample preparation and lower operational costs
• Improved laboratory safety by eliminating hazardous chemicals
• Ideal for high-throughput testing in agriculture, quality control and environmental monitoring

Future Trends and Potential Applications

Integration of portable NIR systems for in-field soil evaluation can support real-time decision making.
Advanced machine learning algorithms may enhance calibration robustness and extend the range of detectable soil properties.
Coupling NIR data with geospatial mapping tools enables precision agriculture, targeted nutrient management and large-scale soil health surveillance.

Conclusion

Near-infrared spectroscopy provides a fast, reliable and multi-elemental approach to soil analysis without the need for reagents or extensive sample preparation. This method supports sustainable land management and high-throughput laboratory workflows.

Reference

• Stenberg B, Viscarra Rossel RA, Mouazen AM, et al. Visible and Near Infrared Spectroscopy in Soil Science. Advances in Agronomy. 2010;107:163–215. DOI:10.1016/S0065-2113(10)07005-7
• Soil Management. University of Hawaii. https://www.ctahr.hawaii.edu/mauisoil/a_fact or_ts.aspx (accessed 2025-05-15)
• Cation Exchange Capacity Fact Sheets. soilquality.org.au (accessed 2025-05-15)
• ISO 11464:2006 Soil quality — Sample preparation. ISO. (accessed 2025-05-23)