Why chemical fertilizers are a losing proposition

Courtesy U.S. Department of Agriculture

by Bruce Sundquist

During the last half of the 20th century global food production tripled because of large increases in the use of chemical fertilizers, genetic engineering of plants (the “Green Revolution”), and large-scale expansion of irrigation systems.

Without nitrogenous chemical fertilizers, the world's farms could only feed two-thirds of today's 6.3 billion people. But with the world’s population expected to grow by two billion by 2050, the world's food supplies are at severe risk for two primary reasons. First, there are no significant reserves of undeveloped cropland available to be tapped, and urbanization, growth of aquaculture, and abandonment of cropland due to erosion and spreading deserts threaten existing croplands. Second, the genetic changes that are the basis of the initial Green Revolution are nearing their theoretical limit.

The so-called Green Revolution has now been reduced to mainly genetic changes that decrease the vulnerability of plants to the pest-du-jour. Unfortunately pests can change their genetic resistance to pesticides and to genetic changes in plants about as fast as people can develop more powerful pesticides and new genetic strains of crops. Also pests are being aided by the shrinking genetic diversity of crops and the vast crop monocultures that are increasingly replacing strip cropping and crop rotation. The net result is that despite massive increases in the use of pesticides and extreme genetic changes to crops, crop losses to pests have not fallen by any clearly measurable amount and remain at about 20-30%. At this point, the Green Revolution is reduced to desperate and increasingly expensive attempts to avoid losing ground and will no longer be able to feed more people as it once did.

Irrigation is also in trouble. Surface waters are now drained to the point where major rivers are not reaching the sea for parts of the year. Aquifers are being pumped dry, and irrigation water is being reallocated to urban use. Salination is also degrading irrigated lands—often to the point of abandonment. And the rates of degradation and abandonment are certain to rise in the decades to come in part because few irrigators can afford to install drainage tiles under their irrigated fields, ensuring their eventual abandonment due to salinity. Most developing nations are too deeply in debt to borrow for such irrigation systems.

Under these circumstances, the only way to accommodate population growth is to pile on more chemical fertilizer. But the tenth ton of fertilizer added to a field produces a far smaller increase in plant growth than the fifth ton, etc. And fertilizer runoff into lakes, reservoirs, and ponds lead to high fish mortality and algae blooms. In turn, algae blooms release toxins that are poisonous to fish and humans. Fertilizer runoffs have already caused about 50 dead zones in the world's oceans.

Worse, chemical fertilizers damage soils. A University of Wisconsin study found that excess fertilization rapidly ages agricultural soils. After 30 years of normal fertilizer application, soil ages the equivalent of 5000 years and loses much of its ability to hold calcium, magnesium, and potassium because of increased acidity. As a result, rich Northern soils are becoming more like the sandy, less productive soils of the South.

Using chemical fertilizer means using less manure, and organic matter makes soil fertile as well as erosion- and drought resistant. While Canada's grain lands have already lost half of their organic matter, farms in Europe, which also use huge amounts of chemical fertilizers, add enough manure to provide half of the nutrient additions to its soils. Unfortunately that option is not available to most farms in the U.S. because our livestock are raised in concentrated feedlots, far from the croplands. In this country the manure just causes huge odor and water pollution problems when it spills over into adjacent streams.

A large part of the world is heavily dependent on the U.S., Canada and Australia for their food imports, but the U.S., formerly the world's largest exporter of food, has recently stopped being a net exporter of food. Canada, with its degrading grain fields, may not be far behind. And Australia, now facing severe salinity and erosion problems and poor soil, may also have to drop its membership in the food-exporters' club.

The only way left to feed two billion more people is to apply massive amounts of additional chemical fertilizers, but because this damages soils, even more chemical fertilizers are needed to compensate. We could also try to escape this Faustian bargain by pushing harder on the productivity of water in our irrigation systems, but this increases salt levels in the soil, which ultimately leads to the abandonment of more croplands, a luxury our world can no longer afford.

Bruce Sundquist is a member of the Allegheny Group where he has served as the Outings Chair since 1976.

Published May 2005