Water resources are also under strain. Excessive and unchecked water extraction for irrigation in many countries has depleted aquifers far faster than they can be naturally replenished. According to the World Water Assessment Programme, about 10 percent of the world’s irrigated land suffers from waterlogging and salinization owing to poor drainage and irrigation practices.
Much of the soil and water degra- dation comes from unsustainable farming practices. Farmers plow their land, for example, to prepare fields for planting, incorporate fertilizers into the soil, aerate soil, and con- trol weeds and pests. But plowing reduces valuable organic matter in soil, disrupts the channels created by roots and worms, and increases the risk of wind erosion. On natural land where vegetation seals in soil and water, soil loss is normally very low: less than half a ton per hectare per year. In contrast, on each hectare of traditionally farmed agricultural
land, farmers lose 45–450 tons of soil a year.
“Most scientists have been working to increase yields for the last 40 to 50 years,” says Spielman. “Only recently have we seen a real awakening around the need for sustainable yields.”
FAREWELL, PLOW In some ways, conservation agri- culture mimics a natural landscape. Because soil is not disturbed and the ground is always covered with plant matter, microorganisms and earthworms do the job of “tilling” the soil and balancing soil nutrients. Te permanent plant cover prevents the soil from getting too hot in tropical climates. In fact, conservation agri- culture has been likened to the floor of the rainforest.
And so, in addition to retiring the plow, conservation agriculture requires permanent ground cover— usually residues from the previous
season’s crop—and regular crop rotation. Te crop residues add or- ganic material to the soil, help retain moisture, and protect against erosion from runoff. Te rotation of crops— particularly legumes—improves soil fertility and prevents buildup of pests and diseases.
For small-scale farmers, conservation agriculture can be less expensive and time consuming than conventional tillage farming. In the areas of the Indo-Gangetic Plains of India where rice and wheat are grown in alternate seasons, a study shows that farmers using conservation agriculture spend an average of US$55 less in cultiva- tion costs, save 50–60 liters of fuel and 15–50 percent of water, and raise crop yields by 247 kilograms per hectare.
Indeed, the practice is now used on an estimated 105 million hectares of farmland worldwide, though still mostly in North and South America and mostly by large-scale farmers cul- tivating soybeans, wheat, and maize.
Source: R. Derpsch and T. Friedrich, “Development and Current Status of No-Till Adoption in the World,” paper presented at the 18th Triennial International Soil Tillage Research Organisation conference, Izmir, Turkey, June 15–19, 2009.
NO-TILLAGE ADOPTION WORLDWIDE [IN MILLIONS OF HECTARES] About 105 million hectares worldwide are now farmed using conservation agriculture or no-till farming. Users are mostly large-scale farmers.
13.5 26.6
CANADA USA
0.2 0.1 0.2 0.7
FINLAND UKRAINE FRANCE SPAIN
0.4 SOUTH AFRICA
1.2 1.3
12.0 0.2
0.3 0.1 25.5 0.7 2.4 0.7 19.7 0.2
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VENEZUELA COLOMBIA BRAZIL BOLIVIA PARAGUAY URUGUAY ARGENTINA CHILE
TOP 6 ADOPTERS
30 25 20 15 10 5 0
AUSTRALIA NEW ZEALAND
KAZAKHSTAN CHINA
Paraguay Australia Canada Argentina Brazil USA
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