Healthy soil could be our best hope in the face of climate change, food crisis and biodiversity loss Katherine Rowland reports.
Soil is the most diverse ecosystem on the planet. Just one teaspoon contains as many as one billion bacteria, which provide vital services to support the growth of plant species and the myriad creatures who feed on them. Without healthy soil, everything from human health and food security to the resilience and biodiversity of the planet is at risk. The earth beneath our feet is so important that geomorphologist David R. Montgomery, author of Dirt: The Erosion of Civilizations, regards its quality and abundance as a measure of whether societies flourish or flounder. In the past, those with poor quality earth typically faced the prospect of dwindling in power or moving on to better lands.
"In today's world we're running out of places to move on to", says Montgomery. "The only option is to develop resilient soils."
However, modern farming has created a paradox. On the one hand, innovations in machinery, irrigation and synthetic fertilisers have boosted crop yields dramatically, making it possible to cull ever larger amounts more from smaller tracts of earth. According to the Food and Agriculture Organization of the United Nations (FAO), agricultural production worldwide is 2.5 to 3 times greater than it was just 50 years ago, even though the amount of land under cultivation has increased by only 12%. On the other hand, the technologies that accomplish these feats can be deleterious to land and water, and all too frequently undermine the central source of this abundance: the soil. One-quarter of the world's food-producing soils are currently degraded or headed in that direction, says the FAO.
In recent decades, the conventional approach to managing exhausted soils has been to turn to outside inputs, like greater amounts of fertiliser and irrigation, to induce crops to grow against the odds. These strategies may increase production and profits in the short term, but, says soil scientist Rattan Lal of Ohio State University, any effective solution requires a long-term perspective.
Lal maintains that it's not only possible to restore our "abused and taken-for-granted" soils - but that efforts to conserve and revive the earth benefit far more than just our own food chain. Healthy soils also deliver a range of essential ecosystem services, high among them being the absorption of atmospheric carbon dioxide. When it comes to strategies for solving the complex equation of climate change mitigation, biodiversity preservation, and safeguarding human security, soil conservation and restoration are "low-hanging fruit", says Lal.
While industrial farming may be one of the central culprits in depleting soils, preserving this resource does not necessarily mean an end to the high yields and profits gained through intensive methods. Matt Liebman is an agronomist at Iowa State University, with expertise in integrated pest management, an approach that looks to the environment to accomplish some of the work of synthetic herbicides, pesticides and fertilisers. On the 22 acres of the experimental Marsden Farm, Liebman and his team planted three plots with different crop rotations. The first was a conventional rotation of corn and soy, raised with regular doses of chemicals, a cycle typical of the American Midwest. On another they planted a three-year cycle that also included oats, and, on the third, a four-year cycle that featured alfalfa as well. The longer rotations also integrated livestock, whose manure was applied as fertiliser. These plots also received chemical inputs, but in judicious amounts, serving "as powerful tools with which to tune, rather than drive, agro-ecosystem performance", Liebman and his research team report.
The results of the nine-year experiment, published last fall in the journal PLoS One, were dramatic. In the more diverse rotations, compared with the conventionally cultivated plot, yields were higher, herbicide use was reduced by up to 88%, levels of freshwater toxicity (caused by chemical run-off) were 200 times lower, and profits were equivalent. There is no one-size-fits-all solution in farming - and some strong resistance to change - but the study suggests that ecosystem services can replace some of the dependence on chemical inputs, preserving the soil, producing food and sustaining farm profits.
One state away in Salina, Kansas, researchers have spent decades refining the idea that the key to soil health is not a matter of inputs, but rather keeping the ground well covered. Plant geneticist and agrarian philosopher Wes Jackson maintains that about 10,000 years ago our early farming ancestors got it all wrong. Before humans left their bold imprint on the earth, perennial plants dominated much of the globe's landscape. But the crops favoured by farming systems, like wheat, rice, corn and soy, are annuals, that need to seed and be replanted each year, and whose shallow, hungry roots deplete precious topsoil. For Jackson, president of the Land Institute, the way out of the modern agricultural mire is to grow perennial crops, which blanket the ground year round, year after year, and whose deep roots extend 6, 10, 12 feet into the earth. His is a vertical vision. On the surface, permanent coverage means that the earth is not subject to the till, and thus never left bare and vulnerable to erosion. Underground, the tangled masses of roots help to enrich and keep the soil intact; the crops also retain greater moisture, which makes them more resilient in the face of drought and high temperatures.
For the past 30 years, Jackson and his colleagues have been crossbreeding annual staples with their wild, perennial relatives, and interest in these technologies is now on the rise, says soil scientist John P. Reganold of Washington State University. This August, the FAO is convening a three-day summit on the promise of perennial crops to improve food security while minimising harms to the earth. To date, plant breeders have not succeeded in producing perennials that yield on a par with annuals, and widespread planting of perennial grains may be 15 to 20 years away. While agricultural economics tends to focus strictly on yields per hectare, Reganold says that if ecosystem services, like soil conservation, drought resistance and carbon capture, were taken into account, perennial varieties would be of greater value, even if they produced less. Their advantages would be especially apparent in regions with marginal soils, such as Sub-Saharan Africa, where annual crops and their reliance on chemical inputs and machinery can hasten erosion and degradation.
The research does not only hold promise for the teaming microbial populations underfoot. It also supports what Reganold describes as the implicit connection between healthy soils and healthy people. The soil is a storehouse of essential nutrients, which are delivered to humans and other creatures through plants. Soil loss and diminishing fertility pose a direct challenge to the food supply, limiting both how much can be grown, and the level of nutrients contained in crops.
Maintaining the nutrient levels of soils may require closing the loop. According to Seth Itzkan, president of Planet TECH Associates, a consultancy focused on trends and innovations, the key to keeping soils healthy and fertile is animals. While today livestock are commonly associated with overgrazing and erosion, Itzkan says their biological waste is necessary to bring soils back. Livestock, managed "holistically", can serve to mimic the environmental benefits of the great herds and their predators that once roamed certain grassland regions of the world - through the continual return of organic matter to the soil.
Holistic land management is a method developed by Allan Savory, restoration ecologist and president of the Savory Institute, which engages in large-scale grassland restoration through livestock. Savory also oversees the Africa Centre for Holistic Management, which uses livestock to restore degraded soils and kickstart arid grounds into health.
Managed correctly, grazing could restore vast areas of degraded grassland
"Grasslands need animals, but they need them in [the] correct way", says Izkan. "The only way not to have deserts in arid areas, in the presence of domesticated animals, is to have grazing done holistically, using a plan that accommodates the diversity and complexity of each situation." Managed in this way, he says that livestock "can effectively and affordably restore vast areas of the world's degraded grasslands with the additional social and climate-related benefits."
Livestock are not the only means by which to restore nutrients to the earth. In Haiti, centuries of poor land management and poverty have steadily impinged on the country's ability to feed itself: between 1979 and 2001, per capita cereals production fell by 34%, and between 1998 and 2000, imports and food aid comprised more than half of the cereals consumed. To boost food security, ecologist Sasha Kramer founded Sustainable Organic Integrated Livelihoods (SOIL), a non-profit organisation that builds composting toilets to help carry organic matter and fertility back into the earth. The EcoSan toilets have separate compartments for liquid and solids, and when they reach capacity, SOIL workers collect them to process the waste into rich dirt, which is then sold to local nurseries and farmers. Kramer, who refers to her work as "liberation ecology", is addressing two problems: the absence of proper sanitation facilities and worn out soils. The solution, which introduces human by-products into the food supply by way of the soil may, rightly, arouse concerns over safety. However, improved methods of destroying pathogens serve the composting process.
Kramer's model may be effective, but it is not new. In China, 'night soil' was used for millennia, and the agricultural terraces of Peru also received ample helpings of man-made fertilisers. "But today we're squandering human waste", says David Montgomery. "A long-term vision of sustainable agriculture returns all organic matter to the soil." Especially as the world's population becomes increasingly city bound, Montgomery contends that societies will soon need to radically rethink urban plumbing and re-evaluate waste for what it really is: the building blocks of soil and new life.
Katherine Rowland writes about health and the environment from New York.