"Weird" Science #2: Soil, Part 1

This post originally appeared on my personal blog. Ported to Forbidden Questions on 11/21/2011.

I've been reading Allan Savory's Holistic Management: A New Framework for Decision Making.

I'm bummed that Savory and/or his publisher try to palm it off as a general management textbook. I'm afraid those who are looking for general management principles and insights will tend to ignore it, because it has a very strong (95% plus) focus on land or soil management. And, I'm afraid, those who should be most interested in it--the students of soil science and/or land management--will ignore it because it won't come up on their radar: "I'm not interested in a generic book about decision-making! I want something about land use, soil conservation, food production, and so forth!"

Well, it is a most worthwhile and interesting book for anyone concerned about these latter subjects. Most worthwhile and interesting, indeed.

Savory teaches--and demonstrates--so many principles that seem counter-intuitive, and go completely opposite standard land management practices.I won't get into too many details, here, but let me point out this one "lesson" I gathered from him. It has to do with letting land "rest." It is a truism amongst most conservationists that a major cause of land degradation and erosion has to do with overgrazing: too much animal and/or human impact. "We need to cordon this area off, so the vegetation can recover. Let's keep animals and people off this land for a few years. Maybe it will recover."

Savory says such a policy is exactly not what is called for. It is a very bad idea.

Oh, yes, land and vegetation need periods of rest, but not for years on end. He provides multiple illustrations of what he is talking about. Two photos, on pages 21 and 22 in his book, are almost all one needs to demonstrate the point:

Why is this?

There are several interlinked phenomena at work, here. I will just mention a couple.

1. "[E]nvironments may be classified on a continuum from non-Bristol's a very brittle according to how well humidity is distributed throughout the year and how quickly dead vegetation breaks down" (p. 28).
    
2. In areas where moisture is less than abundant (i.e., in "brittle" environments), when grasses are permitted to grow without being cut--either by animals who would feed upon them or by humans who may use them for fuel, for thatch, or, for any number of other reasons--the tall, mature growth tends to keep new plants from taking root or flourishing. After a year, the old growth will block new growth. Tall grasses will oxidize standing up. When they eventually fall over, they then create a kind of thatch cover for the soil beneath, providing an effective barrier for any light to hit the soil surface, preventing seeds from germinating, and shedding rainwater before it can soak into the soil. . . .
    
3. By the time the old growth has finally oxidized or decayed away, the soil beneath has become hardened, the crumb structure destroyed. (Savory says soil in this condition is "capped.")
   

   Crumb structure refers to presence of aggregated soil particles held together with "glue" provided by decomposing organic matter. The space around each crumb provides room for water and air, and this in turn promotes plant growth.
   

   --Footnote, p. 108.

   When raindrop impact breaks down the surface crumb structure, it frees the organic and lightweight material to wash away while heavier fine particles settle and seal, or cap, the soil. The importance of surface crumb structure to water penetration is easily demonstrated by comparing a bowl of wheat grains and one of flour. Neither has a hard cap at the outset, but one has large particles, and the other has lost that structure. Pour a jug of water on each bowl and watch. Most of the water soaks into the grains, but it seals the surface of the flower immediately and runs off.
   

   --p. 108.

And the solutions to these problems?

In more brittle environments, the only tool that can provide adequate soil cover over large areas is animal impact. On both range lands and croplands animals can be used to trample down old standing vegetation or crop residues to provide letter. Their hooves can be used to break up there, Soil surfaces, preparing a seed bed in which new plants can germinate. On the very hard-capped soils in the tropics, . . . large hoofed animals are only able to break up soil surface capping progressively or when concentrated in large numbers at very high densities.

--p. 110.

The key, says Savory, is "[r]elatively high numbers of heavy, herding animals, concentrated and moving as they once did naturally in the presence of predators" (p. 37). The disturbance of the soil surface and the removal of excess plant cover actually increases the fertility of the soil.

--I'll call that unexpected and pretty "weird" science. And that's enough of a post for one day!