Climate change in your backyard
Most of us think that soil fertility revolves around the question of what we need to buy and add to soil. When we begin working with a piece of ground, especially if it has been abused, there may be additions we need to make. By all means, find and work with a competent soil consultant from the Agricultural Extension Services, perhaps, if you feel your soil has serious deficiencies or special needs.
But your main focus should not be what purchased inputs you need to add to your soil, but on strategies to maximize the diversity, health and population densities of soil organisms. Three agricultural practices in particular are injurious to soil life:
Monoculture. The growing of a single species on vast tracts reduces diversity of soil life.
Use of harsh chemicals. Many chemicals – whether intended to fertilize crops, suppress disease, or kill insects and weeds – also destroy populations of soil organisms.
Excessive Tillage. Frequent tillage of soil disrupts soil life and robs it of its carbon (organic matter) reserves. The alternative to such destructive practices is to imitate natural soil ecologies, which will: Take advantage of the diversity and population densities of soil organism. While gardeners are unlikely to practice monoculture – to grow nothing but corn, for example – we should constantly find ways to ‘‘mix it up” in how we manage our soil. Crops of different families should rotate over the available ground in succeeding seasons. Diverse sources of organic matter should be used – compost, mulches, cover crops, etc.
Build Better Garden Soil
Feed the soil using sources of fertility grown on the garden or close by. Deep-rooted cover and fertility crops can ‘‘mine” minerals from the deep subsoil and make them available to more shallow-rooted plants. Nitrogen-fixing legumes (beans, peas, alfalfa) can boost nitrogen for heavier-feeding crops. Recycle fallen leaves and crop residues by composting or using them as mulches. Manures and mulching materials may be available from nearby farm and surrounding. If a soil test does indicate the need to add minerals, slow-release rock powders, such as greensand or colloidal rock phosphate, rather than highly soluble chemical fertilizers, which quickly leach into ground water.
Protect and improve soil structure. Plant in wide beds and don’t compact the soil by walking in the growing spaces. Keep the soil constantly covered – by closely – planted crop plants cover crops or mulches. Addition of lime to most clay soils can help ‘‘flocculate” the almost microscopic soil particles into aggregate clumps, resulting in a looser, more open soil structure with better air and water penetration. When tight soil must be loosened, do it with a broadfork rather than a power tiller or even a spading fork to avoid inverting soil layers.
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 earthworms burrows are destroyed – and it can be sometime 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 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 (CO2). 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 CO2, a greenhouse gas in the atmosphere.
The amount of carbon involved are not trivial: Every one per cent 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 CO2 emission: Carbon is bound up in soil in the form of humus. The solution to climate change begins in your backyard.
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