The Value of Soil: A Spatial Perspective

field erosion
Water erosion removing good soil from a field.

Soil scientists like to remind everyone that “soil is not dirt.” They are of course, right, but what is the difference? I would argue that an important distinction is a question of where. Is it somewhere that it is useful, fulfilling its role as supporting life and improving environmental quality? Or has it been moved to a place where it actually causes problems, while the place it came from is also handicapped by the loss of functional ability? When the material is where it belongs, it is soil. When the material is in a place where it becomes a nuisance, then we can call it dirt.

Whether we realize it or not, soil all around the world is providing important services that make our quality of life possible. So let’s talk about quality of life. What supports your quality of life? One could say that access to air, water, food, and shelter are the basic foundation for building quality of life. While we might expect more than these basics, certainly anyone missing these things are going to have problems. Here’s the thing, soil plays an important role in providing each of these.

Top: General landuse distribution in the Lower Peninsula of Michigan. Climate only partially explains the pattern between forests and crop fields. Bottom: Satellite image showing a local shift in landuse. The NRCS soil map indicates the texture for the soil used for cropland is silty clay loam, while the soil used for forest is sand.

Although soils all provide ecosystem services, they are not all the same. Some are better suited for certain roles than others. For example, some are excellent at producing high yields of food crops, while others are better at growing trees for lumber. Also, some can clean water more efficiently than others. We all know that we can’t grow food crops in desserts like we can grow them in humid climates, but it’s not all about climate. The soil can be a limiting factor too. Now there is a “chicken or the egg” type of concept here because climate certainly influences soil characteristics, but there are other factors too. It’s the numerous combinations of these factors that produce the widely varied soil landscape.

Here’s an example where a difference in a soil property affected the determination of how the land should be best used. In Michigan, USA, the climate becomes less ideal for row crops from south to north. This is largely a function of cooler temperatures and a shorter growing season. The spatial pattern resulting from this can be observed in maps showing land use. But there is another pattern within that pattern. Within the climate gradient, there are often row crop fields directly adjacent to plots of forest. They are too close together for the weather to be different, so why did the people choose different uses for those lands? In many cases, the difference is the sand content of the soil. Through experience, the people learned that it wasn’t economically viable to grow crops on the sandier areas and that there was a greater benefit from letting a forest grow there.

Knowing more about the geography of soils helps us better manage our use of the environment. Soil geographers have been using advancements in geographic information technology to figure out where differences in soil properties are with greater accuracy and spatial resolution. Together with precision agriculture technologies, we can analyze and respond to the unique qualities of soil over space and time. This will be a key component for enhancing productive and sustainable agriculture.

So get to know the diversity of soil out there. And work to keep its value, in part by not letting it become dirt.

For more, take a look at:

Does a Country’s Dirt Determine Its Destiny? (Science Magazine)

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