Dirt to Soil

Soil is a living community, not just a pile of dirt. The best insight from this book is that plants and fungi are developing in the soils, and it is useful to think of the microbes as livestock. They have to be fed and kept healthy.

Unfortunately, some of the things we do to increase productivity can harm the life of the soil. More on that later, but first a little more on healthy soil.

Healthy soil does everything better. It is more fertile, absorbs and holds water better, erodes less easily and holds more carbon. The last aspect is salient these days. Good soils can be 7-9% carbon. Most of our soils today less than 2%. Soils alone cannot solve the problem of climate change, but there is a lot of capacity for carbon storage in soils. The big positive in this equation is that adding carbon to soil is just plain good for many other reasons.

We can add carbon to soil directly by mixing in biochar and organic materials, but this is not the most interesting part of what the author says. He talks about carbon being released by plants in a symbiotic relationship with soil fungi and mycorrhizae. The discovery of mycorrhizae is relatively recent and not all the relationships are well understood. I don’t know how much he is talking science and how much he is talking about his own experience, so the details might differ, but the general concept is sound and very interesting. The plants are essentially feeding the fungi and the fungi help feed the plants. In the process, they build soils and sequester carbon.

We can disturb these relationships with herbicides, pesticides and artificial fertilizer. Let me start with the caveat that the author does not oppose the use of all agricultural chemicals but says that we should use less and use them in more targeted ways. It is easy to understand how pesticides and herbicides would have negative impacts, but what about fertilizer? Artificial fertilizers impact the soil community by letting plants “cheat” on growing. They no longer need to draw so much from the mycorrhizal environment, causing the mycorrhizae to decline or die.

The main thrust of his book, however, involves five principles.

Limited disturbance. Limit mechanical, chemical, and physical disturbance of soil. – Tilling disturbs the structure of the soil. It cuts the roots and the mycorrhizae, makes it dry out faster and creates strata, where a hard layer is under the soils that prevents water infiltration.

Armoring the soil is one way to be resilient. The armor is the residue from a previous cover crop and a cash grain crop is growing through the armor. There should be little bare ground. This was one of the causes of the dust bowl. When soil is exposed, it washes or blows away. The author makes an interesting, almost poetic analogy. He says that what plants do is harvest sunshine. When there are no plants, all that is wasted and even becomes negative in drying.

Diversity. Different species of plants and animals occupy different ecological niches. A diverse community can support more total life and that life may be complementary. A diverse community is also more resilient against diseases, pests and stress in general. I drought will affect different communities differently.

Living roots. Keep living roots in soil as long as possible. This is related to the tilling above. Living roots help maintain soil integrity.

Integrated animals. This is a key point. We should probably eat less meat, since that is better for the environment, but eating no meat is bad for the environment. We need livestock to maintain healthy soils. Grassland ecosystems require grazing animals. There are better and worse ways to do this. Over grazing can destroy grasslands, but no grazing also destroys them. Best is “mob grazing” where large numbers of animals are put on the same place for a short time. They eat most of the grass and trample a lot more of it. You would think this is bad, but it puts the carbon into the soil and allows for better regeneration. The author is a fan of Alan Savory. I have written about him before.

Working in any natural system requires constant effort and constant learning. The author is someone like that. I learned a lot from the book and I also enjoyed a lot. I listened to the audio book on my way to and from a conference about clean water in Charlottesville. It was appropriate listening and complemented insights from the conference.