Saving the earth
Modern agricultural practices, especially tillage, are jeopardizing soil fertility. Conservation agriculture can stop and reverse the damage
Soil fertility declined by about 13 percent between 1945 and 1990, according to a 1994 study. This global average disguises far worse figures for Central America (37 percent) and Africa (25 percent). Mechanized tillage, or ploughing, is largely to blame.
But there is a strategy that can prevent, and even reverse, much of the damage: conservation agriculture. Farmers, researchers and agricultural extensionists met recently in Madrid for the World Congress on Conservation Agriculture, jointly organized by FAO and the European Conservation Agriculture Federation. Its aim was to promote this method of crop production, which expands on the trend towards no-till/low-till agriculture. It calls for farmers to leave crop residues on the land to protect the soil from wind, encourage biological activity and create organic matter in the soil.
"Conservation agriculture protects the soil from both wind and water erosion," says Theodor Friedrich of FAO's Agricultural Engineering Branch. "Leaving soil residues on the surface keeps the soil alive. This creates a structure that admits water, so that it reaches the plants' roots and helps the crop -- instead of running off the surface and taking the soil with it."
Begun in the United States in the late 1970s, conservation agriculture was a reaction to growing soil erosion and fertility problems, as well as the spiralling fuel costs that followed the 1973 Middle East conflict. These made tillage an expensive practice.
"The USA remains a leader in conservation agriculture, with about a third of the 60 million hectares of farmland worldwide cultivated in this way," says Dr Friedrich. "But the more dynamic growth can be observed in South America, where there is now an equal area under this approach." Most of this is in southern Brazil and in Argentina, and in Paraguay, where conservation agriculture may now be practised on as much as half the arable land.
FAO began to support conservation agriculture in 1987, working with farmers' associations in South America shortly after they began adopting the practice. Since 1990 the area cultivated under this method in the region has expanded rapidly.
"For South American farmers, conservation agriculture was a question of survival," explains Dr Jose Benites, another FAO proponent of the practice. "Modern mechanized agriculture had had a huge impact on the Brazilian state of Santa Catarina in the 1970s, bringing big increases in yields -- for a time. Then, in the 1980s, nature presented its bill, in the form of erosion, loss of soil fertility and falling yields. For many farmers in the state, it was a stark choice between soil conservation and starvation."
Erosion and exhaustion: the ancient
The most dramatic instance in living memory was the Dust Bowl of the 1930s, in the southern Great Plains of the United States. Grassland had been ploughed to cultivate wheat in the early 20th century. But the crop did not offer protection from the wind, and the soil became dry and loose, an effect increased by the hooves of livestock grazed on it after the First World War. Finally, a serious drought in the 1930s left the earth so vulnerable that a single storm in 1934 carried away 318 million tons of soil. During the decade, about 20 million hectares of land were damaged. A no-till regime and a covering of crop residues would have prevented this.
The presence of organic matter -- plant matter such as the dead roots of former crops -- and soil biota -- living organisms ranging from microbes to moles -- gives structure to the soil by making it aggregate into clumps. But tillage exposes soil organic matter to air, causing it to decay. In its absence, the soil will break down into smaller particles. These are more likely to be blown away by the wind and to become compacted, especially if a heavy tractor is driven over the soil. Then water can't get into it and runs off the surface, taking soil with it. Meanwhile the crops' roots get less water.
The role of conservation
Yields rise because more nutrients and scarce water get to the crop. And there are big fuel and labour savings from not tilling. A few years ago, FAO calculated that conservation agriculture could reduce the cost of soybean production per acre by US $27 in Argentina, US $14 in the United States and US $11 in Brazil.
After a few years, benefits can include:
So what's the catch?
Conservation agriculture has another desirable effect. Plants are made largely of carbon, and when they decay or are burned, they release carbon dioxide, the most significant single 'greenhouse gas' contributing to climate change. With better management, agricultural land the world over can return this carbon to the soil as organic matter, a process known as carbon sequestration.
The Madrid conference called on international organizations to help develop mechanisms to help farmers benefit financially from the fact that they are increasing carbon sequestration.
The conference called for other advances, among them:
Many farmers are already practising conservation agriculture. But an international effort will be needed to ensure that it reaches its full potential.
8 November 2001