The Long-term Effects of Tillage

Many farmers, gardeners and homesteaders avoid monoculture and harsh synthetic chemicals. However, many people committed to sustainable agriculture unknowingly till the soil in ways that inhibit long-term soil improvement.

Tillage of soil releases a flush of nutrients, which can give an impressive initial boost to crop growth. But this surge of available nutrients results mostly from the death of large numbers of soil organisms, whose biomass decomposes rapidly into the soil. These nutrients tend to be in soluble and volatile forms, and if not taken up immediately by plant roots, are leached to groundwater or outgassed to the atmosphere. In the meantime, life cycles of many soil species are disrupted — fungal threads are broken, and earthworm burrows are destroyed — and it can be some time before their populations recover. If the next tillage occurs before they have done so, we have started a cycle which degrades the health and diversity of the soil food web.

One of the worst effects of excess tillage is the loss of carbon bound in the soil in the form of humus. Oxygen is necessary to soil life, which is a major reason we work to improve aeration in soil through creation of looser, more open “pore structure.” Excessive exposure of the soil to oxygen, however, as occurs in heavy tillage, leads to oxidation of the carbon content and its loss to the atmosphere as carbon dioxide (CO_²). Not only is fertility — which is so dependent on humus content — impaired, but high-tillage agriculture is a major, and growing, cause of accumulation of CO_², a  greenhouse gas, in the atmosphere.

The amounts of carbon involved are not trivial: Every 1 percent increase of carbon sequestered in a garden’s soil is estimated to be equivalent to the weight of all the carbon in the atmosphere above that garden, right out to the vacuum of space. By reducing tillage while adding all the organic matter we can, we reverse CO_² emission: Carbon is bound up in soil in the form of humus. The solution to climate change begins in your back yard.