Soil erosion is a significant global problem, warned scientists at a recent conference of the American Association for the Advancement of Science. With world population now projected to increase from around 7.2 billion today to more than 11 billion by the end of the century, this problem will become even more challenging.
Productive soil is necessary to feed hungry people, but as population grows, the land that provides food is becoming less productive; intensive cultivation allows wind and water erosion to carry away fertile topsoil. John Crawford, a prominent soil scientist at the University of Sydney, Australia, notes that 40 percent of the land used for agriculture around the globe is seriously degraded. Crawford says that within a few generations, at the current rate of erosion, there may be little topsoil left. In 20 to 30 years, he warns, providing enough food will be one of humanity’s biggest challenges.
Some claim that this concern is overblown, and that science and technology will ride to the rescue to prevent disaster, as they have in the past. After all, didn’t the Green Revolution in agriculture prevent the forecasted famines expected during the latter part of the 20th century? A key component of the Green Revolution was use of synthetic nitrogen fertilizer. It’s a mistake to believe that this kind of fertilizer can substitute entirely for the loss of topsoil.
One reason is that increasing use of synthetic fertilizer actually hastens erosion. As farmland contains less of the organic matter commonly found in topsoil, it becomes compacted and less absorbent of water. In this situation, water runs off quickly and increases erosion.
Synthetic nitrogen fertilizers cause other problems. Plants absorb relatively little of them, so the remainder ends up in waterways and groundwater. In the waterways, lakes and seas they enter, the nitrogen depletes oxygen needed by fish and other aquatic life. The “dead zone” at the mouth of the Mississippi River, which fluctuates between 3,000 and 8,000 square miles, is the result of excessive nitrogen. The nitrogen fertilizer leaching into the ground can cause nitrate contamination of groundwater and make it unsafe for drinking.
Another problem is that synthetic nitrogen fertilizer is commonly derived from natural gas. As demand for energy increases, the price of natural gas will go up too, thus adding to the cost of food production. That increased cost will particularly impact farmers in poor countries.
Fortunately, agricultural science is not staking everything on synthetic fertilizers to maintain productivity. In recent decades, researchers have come up with strategies to stop erosion from taking such a heavy toll. One of the most promising is no-till farming. It consists of leaving the roots and stubble of a crop in the field after a harvest instead of removing them by plowing up the ground. This organic material helps to hold the soil in place while enriching the soil as it decays.
No-till, however, has the downside of often requiring more pesticide use than regular cultivation. Without tilling, weeds are more likely to be a problem. Pesticides cause environmental harm, and – as a petroleum-derived product – their cost probably will increase.
Providing enough food for a rising human population will indeed be a challenge, and we all must hope for intelligent solutions. One possibility that begs for discussion is limiting human numbers so that they don’t rise to 11 billion by 2100. That projection is not set in stone, and it is not beyond our power to change. Fewer mouths to feed mean less demand on fertile farmland and other precious resources. With fewer people, we can anticipate a better future than the projected future now looming ahead.