How to rebuild our depleted soil and boost crop production

Soil food web - opening the lid of the black box

by Bart Anderson

"Magic" is how humans have customarily described the soil's natural cycles of decay and growth. Without a scientific understanding, our ancestors relied on observation and traditional practices to grow crops.

Modern chemical agriculture has been only marginally better at understanding the soil. Unable to control the natural cycles, it bypasses them with synthetic fertilizers and pesticides. Despite the outward successes of modern agriculture, its heavy-handed approach brings with it pollution, soil degradation and other ills.

In contrast, organic methods like permaculture have attempted to work with natural cycles. Despite the many insights and successful practices that have emerged, a rigorous scientific model is still lacking. Permaculture and its brethren are accused of being belief systems rather than science. It's hard to make progress without having a common understanding of how things work.

Recently, however, soil ecology has developed to the point where we can open the lid on the black box of underground processes. We can begin to understand how micro-organisms maintain the structure and fertility of the soil. We learn that symbiotic relationships between plants and micro-organisms are not the exception but the rule.

It is no longer just compost-lovers who are excited about soil. The respected journal Science devoted an issue to "Soils: the Final Frontier" (June 11, 2004), saying:

"In many ways the ground beneath our feet is as alien as a distant planet. The processes occurring in the top few centimenters of Earth's surface are the basis of all life on dry land but the opacity of soil has severely limited our understanding of how it functions.... However, perspectives are beginning to change... Interest in soil is booming, spurred in part by technical advances of the past decade."

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Eating Fossil Fuels
by Dale Allen Pfeiffer

SNIP

Soil, Cropland and Water

Modern intensive agriculture is unsustainable. Technologically-enhanced agriculture has augmented soil erosion, polluted and overdrawn groundwater and surface water, and even (largely due to increased pesticide use) caused serious public health and environmental problems. Soil erosion, overtaxed cropland and water resource overdraft in turn lead to even greater use of fossil fuels and hydrocarbon products. More hydrocarbon-based fertilizers must be applied, along with more pesticides; irrigation water requires more energy to pump; and fossil fuels are used to process polluted water.

It takes 500 years to replace 1 inch of topsoil.²¹ In a natural environment, topsoil is built up by decaying plant matter and weathering rock, and it is protected from erosion by growing plants. In soil made susceptible by agriculture, erosion is reducing productivity up to 65% each year.²² Former prairie lands, which constitute the bread basket of the United States, have lost one half of their topsoil after farming for about 100 years. This soil is eroding 30 times faster than the natural formation rate.²³Food crops are much hungrier than the natural grasses that once covered the Great Plains. As a result, the remaining topsoil is increasingly depleted of nutrients. Soil erosion and mineral depletion removes about $20 billion worth of plant nutrients from U.S. agricultural soils every year.²⁴ Much of the soil in the Great Plains is little more than a sponge into which we must pour hydrocarbon-based fertilizers in order to produce crops.

Every year in the U.S., more than 2 million acres of cropland are lost to erosion, salinization and water logging. On top of this, urbanization, road building, and industry claim another 1 million acres annually from farmland.²⁴ Approximately three-quarters of the land area in the United States is devoted to agriculture and commercial forestry.²⁵ The expanding human population is putting increasing pressure on land availability. Incidentally, only a small portion of U.S. land area remains available for the solar energy technologies necessary to support a solar energy-based economy. The land area for harvesting biomass is likewise limited. For this reason, the development of solar energy or biomass must be at the expense of agriculture.

Modern agriculture also places a strain on our water resources. Agriculture consumes fully 85% of all U.S. freshwater resources.²⁶ Overdraft is occurring from many surface water resources, especially in the west and south. The typical example is the Colorado River, which is diverted to a trickle by the time it reaches the Pacific. Yet surface water only supplies 60% of the water used in irrigation. The remainder, and in some places the majority of water for irrigation, comes from ground water aquifers. Ground water is recharged slowly by the percolation of rainwater through the earth's crust. Less than 0.1% of the stored ground water mined annually is replaced by rainfall.²⁷ The great Ogallala aquifer that supplies agriculture, industry and home use in much of the southern and central plains states has an annual overdraft up to 160% above its recharge rate. The Ogallala aquifer will become unproductive in a matter of decades.²⁸

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