Infrared (IR) Spectroscopy is a versatile analytical technique that can characterise a wide variety of different sample types e.g. from drugs and plastics to soil and minerals. The IR spectrum produced is a chemical “fingerprint” or profile of a sample and allows us to “see” what it is made up of.
For soil, both the organic matter and minerals can be identified in the spectrum. We have been using IR analysis in our soil research both to gain insight into differences and changes in soil, and as a tool to predict soil properties. This powerful technique can be used for soil monitoring and in studying soil function and resilience to change.
StageWork in Progress
The overall aim our soil research is to increase the amount of land being managed sustainably and to ensure that Scotland’s soil’s many vital functions are safeguarded.
We are tackling our research aims in two main ways. The first relates to soil monitoring and management and the second to studying the soil’s resilience to change. The research work we are doing involves developing quick techniques, using IR Spectroscopy, for soil monitoring and for providing information that can be used in the modelling of soil functions.
IR Spectroscopy has the potential to give accurate predictions of many soil parameters from a single scan of a soil sample, and therefore provide a time saving, cost-effective and environmentally friendly means of soil monitoring – for all soil types from agricultural soils to peatland.
For example, peatland condition is of increasing importance as peatland is in decline, as much as 80% is estimated to have been damaged, affecting the ecosystem services provided and leading to increases in greenhouse gas emission. The development of methods, such as for rapid assessment of peatland condition, is necessary to allow wider monitoring.
In relation to the ability of soil to resist change, there are many complex questions to be answered and the purpose of our research has been to apply IR spectroscopic analysis to address some of those issues. The issues we are studying have included changes in soil over time, changes in soil with land use change and assessment of the susceptibility of soil to erosion.
A large proportion of our research has been on the National Soil Inventory of Scotland (NSIS) dataset, a Scotland wide dataset of soils sampled on a grid pattern over the country.
We have used two different but related techniques, Near Infrared (NIR) and Fourier Transform Infrared (FTIR) Spectroscopy, which cover different parts of the infrared spectrum, to record spectra.
We have created a unique and powerful spectral dataset for Scotland, which gives the chemical profile of every distinguishable layer of the soil (or soil horizon) at each of the 183 sites on a 20 km grid. We have been able to use the spectral data to “visualise soils” and changes going down the soil profile, from the surface to the rock below, looking at things such as changes in soil organic matter (SOM) and the type and relative proportions of clay minerals. Both SOM and clay minerals play very important roles in the way that soils function, for example determining whether soils are freely or poorly draining.
The NSIS dataset was sampled in the 1970s/80s (NSIS1) and then resampled between 2007-2009 (NSIS2) which has given us the ability to look at changes over time – e.g. changes in SOM after land use change. Using the spectral datasets, and a range of statistical approaches, we have also successfully developed models which allow us to predict multiple chemical and physical soil properties for a sample, without the need for “wet chemistry” which takes longer, costs more and is more environmentally unfriendly.
Through analysis of a range of other datasets (including peatland, machair soils (rare coastal soils found in the Hebrides) and agricultural soils) we have also shown that FTIR can be used to monitor the condition of our peatlands and that spectral data can be correlated to the susceptibility of soils to wind and water erosion.
The IR NSIS spectral database we have created is a unique resource for our future, with the potential to be applied to many different types of soil research. It has also validated the high quality of the procedures used in sampling and processing soils for the NSIS dataset.
We have also shown that the models we have developed, using NIR and FTIR spectral data, can reliably be used for prediction of a range of soil properties and it has been possible to use the predictions where measured data wasn’t available. For example, we have predicted soil bulk density (BD) values for NSIS soil samples allowing changes in carbon stocks for Scotland’s soils to be calculated and this wouldn’t otherwise have been possible.
Building on the success of the FTIR models for prediction of soil properties we are now working on the development of field-based methods which would vastly improve how often, and the scale of soil sampling, which is possible. The data generated could also form the basis for carbon accounting systems for the soil or potentially be used in precision agriculture.
Methods we have developed through our research have also been applied to other external projects. We have contributed to projects looking at changes in carbon stocks after afforestation (Forest Research project); working on assessing soil in relation to oak tree health (PuRpOsE project); and assessing changes in the soil organic matter for an Agriculture and Horticultural Development Board (AHDB) project on crop and soil rotation.
Our expertise, particularly using FTIR spectroscopy for soil analysis, has been shared with scientists from across the global research community, highlighting not only benefits to Scotland but also internationally. Development of new methods, such as the spectroscopic methods we have developed for soil analysis, are critical in allowing current research to be extended beyond existing boundaries and new areas of research to open up.
- The Power of Infrared Analysis in Agriculture: Unique Insights into Soil, Crops, Vegetation and Fungi
- Spectroscopy and Remote Sensing for Assessment of Peatland Degradation
- Changes to C Stocks in Scottish Soils due to Afforestation
- How to minimise loss in spectral quality when going from laboratory to field measurements using a portable FTIR instrument
- Field based Soil Analysis: Portable FTIR and XRF
- On using the Precise Sensor
- A Robust FTIR Database for Scotland
- Extending Predictions of Soil Parameters for a National Dataset
- Global and Local Calibrations to Predict Chemical and Physical Properties of a National Spatial Dataset of Scottish Soils from Their near Infrared Spectra
- Spatial trends in the wind abrasion resistance of cultivated machair soil, South Uist, Scottish Outer Hebrides
- Soil Spectroscopy: An Alternative to Wet Chemistry for Soil Monitoring
- Comparison of soil carbon stocks in Scottish soils between 1978 and 2009