United States Department of Agriculture, US Conservation Services, image of soil in cross-section.

O: Humus: the top layer of decayed organic material (often dead leaves).

A: Topsoil: Below O is topsoil, rich and dark, after further decay from organic material above and from life in the soil. With the resident life it is nutrient-rich and holds water. A relatively thin layer, this is mostly what we mean by soil, say in your garden or when you buy a bag of potting soil.

B: Subsoil: A thicker layer below A that the roots can grow into. Some organic matter, but much less. It is mostly bits of rocks (weathered or deposited in some areas by previous glaciers) and clay (clay itself is made up of bits of very fine rock material, silica or magnesia, with some other minerals as well, and water, and some organic matter that is pressed down over time).

C: Weathered material and rocks, dense and not penetrated by roots, with little organic material. There is weathered “parent material” which can be several materials: bedrock, deposits of rocks mixed with sand and clay.

R: Bedrock (not shown)

We need the O, A, B and C levels to survive. Without them we have barren clay and rock (well, maybe some moss and the like could survive).

The problem

Due to climate change and poor agricultural practices, much of our soil is anything but healthy. And it is disappearing, being blown or washed away.

If soil is too dry due to a change in climate, it may be considered aridifcation. If the soil is basically gone, as in a desert, the term is desertification. These are major global problems.

Plants expire water they obtained from the soil, and enough trees can cause microclimate changes that include local rain, as has been seen, for example, in the Amazon tropical rain forrest! A positive cycle to combat the effects of droughts and decrease risk of severe wildfires.

We are running out of soil and depleting the soil we have left of nutrients and the ability to hold water.

When that process goes to its logical endpoint we have desertification, that is, we turn farmland into desert.

You might be familiar with the “dust bowl” in the American heartland in the 1930s; think of the novel and movie Grapes of Wrath. It is happening all around the world right now.

Physically losing soil to erosion isn’t the only problem. We tend to grow the nutrients out of the land and then poison it, severely degrading the soil, turning it into a pale, sickly version of its organically rich former self.

Some estimate that we are going to be out of useful soil in 60 years or so! In fact, if 60 means the soil is essentially gone, we are in deep trouble already and will likely have devastating problems within a generation if nothing is done. That is, soil loss, soil degradation, and aridification/desertification, may have major impacts on human life and civilization before the worst effects of global warming take hold! 

The problem directly is less ability to grow sufficient food, and indirectly the immense suffering from the psychological, physical, economic and social disruption that entails.

Further, soil sequesters carbon in the O, A and B levels. Releasing that carbon by plowing the fields aggressively and losing the ability to sequester more carbon makes climate change worse!

From the point of view of planetary health, clearly malnutrition is not good for you. Even when there isn’t frank starvation or famine, these soil changes can decrease crop yields, disrupt society and be a huge economic burden.

Further, we must keep in mind that the most economic crops and methods of farming may not be best for soil or people. We plant for calories (e.g., corn, often used as sugar in the form of corn syrup, added to many products), not a range of healthy foods and sources of protein. This leads to obesity and poor nutrition which impacts many diseases (e.g., diabetes). Trying to keep up production also leads to harsh working conditions and the use of chemicals with potential exposure to humans and ecosystem damage (e.g., pesticides, loss of pollinators).

Why are we losing soil so rapidly?

Poor agricultural practices are the main cause of soil loss and degradation. The need for growing sufficient food rapidly for our growing world population, combined with practices that encourage erosion or poor root structure, are the main drivers of soil loss and degradation.

Tilling soil is a major contributor to the problem as it disrupts the layers and loosens the soil so that the wind and rain carry it away more easily. Tilling also causes water held in the soil to evaporate and disrupts the soil ecosystem.

Climate change and the resulting extreme weather events and droughts exacerbate this problem and the human toll it has. Heavy rain and floods wash off more soil, especially loose, tilled soil. Less rain and more heat-induced evaporation means drier soil that wind can erode.  Both can happen in the same area at different times!

Further, many of the social, economic and health effects of global warming are worse when it is harder to grow quality food in sufficient quantities. And the social disruption with the movement of people, and need to mechanize food production and transport it farther, further adds to global warming and ground, water and air pollution.

High-tech answers like hydroponics or clever ideas like roof gardens and vertical farming, as well as home gardens, can play a role in feeding some of us, but are either too expensive or won’t scale up enough, or both, to make a large dent in our looming food scarcity.

This brings us to sustainable agriculture.

Sustainable agriculture

Sustainable agriculture means techniques that don’t destroy our ability to grow food in the future.

There are many ways to farm that are proven to retain soil. Mostly they are techniques that prevent erosion or depleting the soil of nutrients and organic material.

For example:

• Minimizing tilling, even no-till farming (though that is often teamed up with chemicals to control weeds)

• Terracing on hills (water and soil run faster downhill) and using ledges to prevent water and soil run-off

• Planting crops with deeper roots (including trees) so the soil and water are held in place better

• Systems using targeted irrigation (e.g., drip irrigation) and systems for capturing rain water and soil that are being washed away

• Having cover crops so the land isn’t bare to the wind and rain after harvest of the main crop

Though it takes education and some extra effort and expense, they are investments that would pay great dividends.

Improving soil health:

• Rotating crops, especially with nitrogen-fixing food plants

• Rotating fields for livestock grazing

• Amendments that add organic matter like cover crops, manure, biochar (specially heated organic matter to a charcoal with minimum release of CO2, so a carbon “sink”), and compost

Composting is not only great for producing fertilizer for food and other plants, the composted food doesn’t enter landfills, where it produces methane, a powerful greenhouse gas! Feeding food waste to worms is a great form of composting. It isn’t scalable enough to make a huge dent, but it is fun.

Composting is possible on industrial scales. There is a new statewide mandate for composting in California, though it will take a while to get up to speed.

San Francisco already collects 650 tons/day of compostable material converted to about 350 tons of compost. This saves 93,437 metric tons of CO2e per year, and that is just one city!

“Regenerative” agriculture techniques, include using perennial and cover crops, minimizing tilling, appropriate crop rotation and animal husbandry.

Using agricultural waste to make biochar (organic material burned in a process that retains more carbon than it releases as CO2) can lock up vast amounts of carbon according to Wayne Visser in Thriving.