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Soils in the digital age

Soil map of Tayside (c) James Hutton Institute
"As our understanding of how soils are formed and how their character is influenced by the environment increases, we become better at mapping the soil without even looking at it

Dr Matt Aitkenhead, Information and Computational Sciences, James Hutton Institute

Why do we need to monitor soils? For people whose livelihoods depend on the soil, knowing its character in one place or another will make a huge difference in how the soil is treated, or what can be expected of it. And in many parts of the world, we had very little idea until recently about what the soils were like. Did they contain a lot of carbon? What use were they for growing local crop types? Were they likely to suffer from erosion? We just didn’t know, and so soil surveyors had to go and find out.

Historically, direct observation with the senses was the only way to get information on soil. It might sound surprising – and a little disgusting – but professional soil surveyors will often use all five senses to describe soil ‘in the field’. Sight is obvious, but what about touch, or hearing? And how do taste and smell come into it? Rather than give you the answers, we suggest that you do something even better – go outside, find some soil, and work it out for yourself!

Soil mapping has been closely linked to technology that is available. Until about twenty years ago, this meant hand-drawn paper maps that were useful but bulky and fragile. Also, any new information meant that the map had to be re-drawn from scratch. Nowadays, soil mapping has been revolutionised by the use of GPS (for precise location of features) and GIS (for producing digital maps that can be altered more easily and transmitted electronically).

However, we still have to get the data before it can go into the map. One of the oldest approaches, and still in many ways the best, is laboratory-based ‘wet chemistry’ analysis. Samples are brought back from field sites and their chemical composition is determined using a number of different approaches.

More recently, we have come to use spectroscopy. This involves looking at the light reflected or absorbed by the sample at lots of different wavelengths and using this information to determine sample characteristics. Many wavelength ranges can be used, from the ultraviolet through the visible and all the way into the infrared. The methods involved vary, but one thing is always important – different soils interact differently with certain wavelengths of light, and once we know this information we can use it. This also allows us to look at stored samples obtained years ago and extract new information from them.

It is also possible to take photographs of the soil with a standard digital camera to work out some fairly basic information, such as how much organic matter it contains or whether it is coarse or fine-textured. This has the potential to allow rapid assessment of soil condition in the field using nothing more sophisticated than a mobile phone.

Another way of looking at the soil is from above. Remote sensing covers the use of satellites, planes and in recent years UAVs to monitor the Earth. While most remote sensing can only see the first topmost material (usually the vegetation), some sensors operate in wavelengths that allow them to detect moisture or carbon in the soil. Remote sensing can also be used to detect patterns in the landscape. These above-ground patterns often relate to the distribution of soil characteristics.

This brings us back to that digital mapping of soil. Technological developments such as GPS and GIS are not our only tools in this. As our understanding of how soils are formed and how their character is influenced by the environment increases, we become better at mapping the soil without even looking at it. Using existing soil data from survey work and knowledge on how soils form, we have become able to produce high-resolution digital maps of soil character that can be useful for a wide range of topics, from agriculture to engineering.

An important part of modern soil monitoring and mapping is the integration of data from multiple sources. Remote sensing data might tell us something, but not everything. The same is true of spectroscopy, or linking information about topography, climate, vegetation and geology to make predictions of soil character. None of these approaches is the silver bullet, which is why we work hard to bring the results of each together into a more useful whole. The future of soil monitoring and mapping is going to involve a lot of data, and we need to find new ways to handle and use it.

An important point to finish on is that while we can use existing data and stored soil samples in new and clever ways to monitor and maps soils, we will never remove the need to go out and have a look at the soil and bring back new samples. Soils change and our theoretical knowledge is never perfect, so from time to time you will still see soil surveyors out in the field, happily digging away. Looking, touching and listening. And yes, smelling and tasting!.

This article was originally published in the Summer 2015 issue of The Geographer, the magazine of the Royal Scottish Geographical Society, and has been reproduced by kind permission of the RSGS.

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The James Hutton Research Institute is the result of the merger in April 2011 of MLURI and SCRI. This merger formed a new powerhouse for research into food, land use, and climate change.