NewScientist‘s Joshua Howgego investigates how the variety of soils on Earth is changing in response to human farming habits:
FIND the places where farms give way to the California wilderness and you’re sure to encounter an endangered species. It is not aggressive, but it is omnivorous, devouring anything that happens to fall dead within its reach. And like most rare beasts, the extinction of Abruptic durixeralfs would have cascading impacts on the ecosystem around it.
Don’t be misled by the name. This is neither animal nor plant nor microbe, but a subgroup of soils. Its members nonetheless slot into a classification system every bit as elaborate as that we use to categorise life forms. In the US alone, more than 20,000 soils have been catalogued. Many are facing extinction.
Soil Taxonomies are summarized by Wikipedia and covered academically by this lesson from the University of Nebraska-Lincoln:
The nature and properties of soils can vary widely from one location to the next, even within distances of a few meters. These same soil properties can also be found to exhibit similar characteristics over broad regional areas of like climate and vegetation. The soil forming factors of parent material, climate, vegetation (biota), topography, and time (Principles Lesson 3.2) tend to produce a soil that describes the environment in which it is formed. By surveying properties of soil color, texture, and structure; thickness of horizons; parent materials; drainage characteristics; and landscape position, soil scientists have mapped and classified nearly the entire contiguous United States and much of the rest of the world.
So what’s the problem? From Joshua:
Agriculture is by far and away soil’s biggest problem. In the wild, nutrients removed by plants are returned to the soil when they die and decay to form rich humus. Humans tend not to return unused parts of harvested crops to replenish those nutrients.
We realised this long ago and developed strategies to get around the problem. We left fields fallow, or rotated crops that required different nutrients, thereby keeping the soil in balance. Growing peas and beans can even add nitrogen, a vital nutrient, to the ground: nodules in their roots host rhizobia bacteria, which grab atmospheric nitrogen and convert it into nitrates.
But over the past few decades, it has become clear this wasn’t such a bright idea. Chemical fertilisers can release polluting nitrous oxide into the atmosphere and excess is often washed away with the next rain. This leaches nitrogen into rivers, damaging algal blooms. More recently, we have found that indiscriminate fertiliser use hurts the soil itself, turning it acidic and salty. It also suppresses symbiotic relationships between fungi and plant roots, and can even turn beneficial bacteria against each other.
And current status?
… we are losing soil at a rate of 30 soccer fields a minute. If we don’t slow the decline, all farmable soil [world-wide] could be gone in 60 years.
The International Soil Reference and Information Centre has released a map of currently known soils throughout the world.
