The debate over sustainable agriculture has gone beyond the health and
environmental benefits that it could bring in place of conventional industrial
agriculture. For one thing, conventional industrial agriculture is heavily
dependent on oil, which is running out; it is getting increasingly unproductive
as the soil is eroded and depleted. Climate change will force us to adopt
sustainable, low input agriculture to ameliorate its worst consequences, and to
genuinely feed the world.
But in order to get there, important changes have to be made in
international agencies and institutions, which have hitherto supported the
dominant model of industrial agriculture and policies that work against poor
countries, where farmers are also desperately in need of secure land tenure.
This mini-series is a continuation of many articles that have appeared
in our magazine, Science in
Society since 2002.
Research has shown that declining crops yields are, in most cases,
exponentially linked to loss of soil quality. Soils are threatened by water and
wind erosion, nutrient depletion and salinisation, among other things.
Although, on a global scale, soil loss is unlikely to be a major threat
to food security, the impacts are probably going to be felt acutely at the
local and regional levels. This is especially so where farmers are too poor to
curb or overcome the damage.
Mechanized agriculture has caused billions of tonnes of carbon
previously trapped in soil to be released to the atmosphere as carbon dioxide and methane. Lack of carbon in the soil
makes crop production inefficient and constrains yields.
Global warming is likely to make things worse. As the ground heats up,
organic matter decomposes more easily, reducing soil fertility, releasing
carbon dioxide and further exacerbating the warming effect. In fact, soil
erosion already contributes to global warming, as some of the carbon in
soil-laden water running off fields inevitably escapes into the atmosphere.
Deserts are expected to expand as the interiors of continents become drier, and
erosion would worsen if soils dried out and violent storms became more
Inevitably, a hotter world is likely to have less organic matter in its
soils. This will have tremendous consequences for farmers the world over,
particularly for those farming in the marginal areas of developing countries.
Critical regions of soil degradation and hence a high priority for soil
restoration and carbon sequestration (storing carbon in soil securely so it is
not immediately reemitted) include sub-Saharan Africa, central and south Asia,
China, the Andean region, the Caribbean, and the acid savannas of South
Fortunately, something can be done, by managing soils to stem erosion
and retain more carbon. Carbon sequestration can potentially offset global
fossil fuel emissions by 5-15% each year, while raising yields. Once
sequestered, carbon can remain in the soil, for the next 20-50 years at least,
as long as appropriate management techniques are used.
One proven method of resisting erosion, restoring soil fertility and
boosting crop productivity is the use of organic compost. Compost is a natural
fertilizer, supplying soils with vital plant nutrients, and aiding them to
retain water and air. It restores soil carbon, crucial in maintaining
consistent yields through improvements in water and nutrient holding capacity,
soil structure and biotic activity. Compost improves soil texture and
structure, and helps control weeds, pests and diseases.
The implications of practices such as composting could be enormous for
food security. According to Rattan Lal of the Carbon Management and
Sequestration Centre at Ohio State University, a one tonne increase of the soil
carbon pool in degraded soils may increase crop yield by 20 to 40 kilograms per
hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for
cowpeas. In Ethiopia, farmers using compost increased yields for various food
crops, sometimes doubling or even tripling yields. The yields from using
compost are comparable, and often higher, than those from chemical
Already, agricultural experts are urging Malawian subsistence farmers to
use organic compost, instead of manufactured fertilisers. Samuel Saka,
agricultural development officer for Nkhunga extension planning area in
Nkhota-Kota district in central Malawi said, "Based on the successful
demonstration plots we had, many farmers have started implementing this method
and the results speak for themselves - high maize yields."
A nationwide campaign is being promoted, as prices of manufactured
fertilisers are skyrocketing, putting them beyond the reach of most Malawian
subsistence farmers. As compost is affordable and can be prepared from a
combination of readily available material such as dry leaves, grass, maize
stalks and other biodegradable substances, it can be made and used by poor
farmers. There is no need to borrow money, so farmers do not have to take
credit and get into debt as they often do when using chemical fertilizers.
The materials to make compost are mixed with soil and water, then left
to decompose for some time. The heat generated during the process destroys most
weed seeds, fungal diseases, parasites and pests. Although farmers do have to
invest time and labour into making good compost, the rewards are worth the
effort. The positive effects of compost on yields last for two or more growing
seasons, so soil given compost in one year need not be treated again the next
Other strategies exist for combating soil degradation, and should be
used together with compost. For example, in developing countries, sowing cover
crops, using green manures and crop residues, and planting trees have restored
soil fertility and stemmed erosion. In general, recommended strategies to
rehabilitate degraded soils and increase soil carbon are also sustainable
agricultural practices. The combined benefits of restoring soils, increasing
yields and helping limit climate change are too important to ignore.