In the previous post, we learned about soil compaction. This is one aspect of soil structure. Another aspect is layering.
We all know about topsoil: it’s the valuable layer of soil closest to the surface, that is rich with nutrients and other resources. Below this are other layers, or horizons, which are primarily of interest to soil scientists.
The point we will focus on today is that layers should stay where they are. When each type of soil is at the right depth, the plant community living on top of the soil thrives. When layers are all mixed up, plants suffer.
Mixing within a layer isn’t good for plants either. A third aspect of soil structure is the very specific way that particles are arranged in the soil. When clumps of sand or clay, water droplets, air pockets, and microorganisms get jumbled out of their proper places, soil ceases to function in the way that it’s supposed to.
What can cause this kind of jumbling? Plowing, an agricultural practice familiar even to non-farmers, is the process of deliberately scrambling soil. In other words: plowing is bad for soil.
Why would farmers engage in a practice that damages soil? The answer is that plowing boosts plant growth in the short term. By turning over the first few inches of topsoil, farmers can introduce more air to the soil. While air in soil is good, this is a case where too much of a good thing is not better. Soil microorganisms gorge themselves on the extra oxygen, and start breaking down organic matter in hyperdrive. That makes lots of nutrients available to plants, which consequently grow very vigorously.
The problem comes when those voracious microorganisms run out of organic matter to decompose. Then the amount of nutrients available to plants suddenly drops, leaving them struggling to survive. Farmers start feeding their plants artificial fertilizers in an attempt to maintain their yields from the depleted soil, and the whole system becomes expensive, unproductive, and environmentally damaging.
The practice of rapidly wearing out soil was not much of a problem when there were few people, when the American plains seemed to go on forever, and when farmers could plan to just move to a new quarter-section every few years. Now that pretty much all the land is spoken for, farmers need to farm as if they intend to stay where they are. Plowing is not a form of sustainable agriculture – and, indeed, the practice of no-till farming is becoming increasingly popular.
But many gardeners still use residential-scale equivalents of plowing, like rototilling and double digging. Just like with plowing, these practices increase fertility in the short term, but result in damaged soil that can’t sustain plant life over the long term. Many gardeners now are adopting practices that involve disturbing soil as little as possible.
People today have different knowledge and different values than people in the past. Plowing was once an iconic practice in the agricultural landscape. Now we know better ways of sustainably managing our land.