THOUGH TOPSOIL erosion, lamented David Pimentel of Cornell University, is second only to population growth as the biggest environmental problem facing the world, it is difficult to get people excited about dirt. Unless we are told that our food security depends on it. Almost all our food — 99.7 percent of it — comes from cropland that is shrinking by more than 10 million hectares a year due to soil erosion.
Only last year, the world lost an estimated 24 billion tonnes of topsoil — blown off by wind, washed away by water, made sterile by chemicals or simply covered with concrete. That is a loss of 3.4 tonne per person in just 12 months. By 2050, we may end up losing more than half of even what remains.
Nearly 40 percent of soil used for agriculture around the world is classed as either degraded or seriously degraded, which signifies a loss of 70 percent of the topsoil. Experts such as John Crawford of University of Sydney estimate that at the current rate, there is only about 60 years of topsoil left. That means business as usual may lead to starvation in our children’s lifetime, if not earlier.
Topsoil is the thin layer of earth that supports plant life with nutrients. It is packed with micro-organisms that recycle organic material and enhance the soil’s ability to retain water. Deforestation is a major trigger for erosion. Conventional agricultural practices involve burning or removal of crop residue, over-ploughing, overuse of chemicals and, at times, overgrazing. All of these result in loss of soil carbon, which is essential for microbes to thrive.
Loss of topsoil leads to lower productivity. Soil degradation will reduce food production by 30 percent in 20- 50 years. Even moderately degraded soil will hold less than half the water that healthy soil does.
At the other end, about 60 percent of the washed away soil ends up in rivers, streams and lakes, triggering floods. Erosion also leads to more air pollutants and the blownoff soil carries about 20 organisms, spreading diseases such as anthrax and tuberculosis.
The threat is most acute in China, Africa, India and parts of South America. It is also a serious problem in sub-Saharan Africa, where the Millennium Villages initiative by New York’s Columbia University has shown that by countering depletion of soil nutrients, it is possible to more than triple grain yields.
Across India, about one millimetre of topsoil is being lost each year with a total loss of 5,334 million tonnes annually due to erosion. This amounts to a monetary loss of over Rs 1,000 crore. According to a study by Dehradun’s Central Soil Water Conservation Research and Training Institute, the rate of loss is 16.4 tonnes per hectare every year. In other words, we are losing every year what takes at least 20 years to be replenished.
TEHELKA visits Medak district in Andhra Pradesh where farmers are destroying the soil with chemicals. We also venture into ‘Timbaktu’ in Anantapur district, where patient tillers have let the earth heal itself.