Outgrowing the Earth: The Food Security Challenge in an Age of Falling Water Tables and Rising Temperatures


Lester R. Brown

Chapter 4. Raising the Earth’s Productivity: Fertilizer and Irrigation


In 1847 Justus von Liebig, a German chemist, discovered that all the nutrients that plants remove from the soil could be replaced in chemical form. This insight had little immediate impact on agriculture, partly because growth in world food production during the nineteenth century came primarily from expanding cultivated area. It was not until the mid-twentieth century, when land limitations emerged, that fertilizer use began to climb. 17

The rapid climb came as the frontiers of agricultural settlement disappeared and as the world began to urbanize quickly after World War II. With little new land to plow, growth in the food supply depended largely on raising crop yields. And this required more nutrients than were available in most soils. When the world was largely rural, plant nutrients were recycled as both human and livestock wastes were returned to the land. But with urbanization, this natural nutrient cycle was disrupted.

The shift from expanding cropland area to raising cropland productivity, coupled with accelerating urbanization, set the stage for the growth of the modern fertilizer industry. It also laid the groundwork for researchers to do elaborate soil testing to determine precisely which nutrients farmers needed to apply and when. It enabled farmers to remove nutrient constraints on yields, thus helping plants to realize their full genetic potential.

The growth in the world fertilizer industry after World War II was spectacular. Between 1950 and 1989, fertilizer use climbed from 14 million to 146 million tons. This period of remarkable worldwide growth came to an end when fertilizer use in the former Soviet Union fell precipitously after heavy subsidies were removed in 1988 and fertilizer prices there moved to world market levels. After 1990, the breakup of the Soviet Union and the effort of its former states to convert to market economies led to a severe economic depression in these transition economies. The combined effect of these shifts was a four-fifths drop in fertilizer use in the former Soviet Union between 1988 and 1995. After 1995 the decline bottomed out, and increases in other countries, particularly China and India, restored growth in world fertilizer use. (See Figure 4–1.) 18

Among the big-three grain producers, China is the leading user of fertilizer, with the United States a distant second. India is now closing the gap with the United States and may overtake it within the next several years. (See Figure 4–2.) 19

In many agriculturally advanced countries, fertilizer use has plateaued. For example, U.S. fertilizer use is essentially the same today as it was in the early 1980s, between 17 million and 21 million tons a year. Usage has also plateaued in Western Europe and Japan and will soon do the same in China as well. 20

There are still some countries with a large potential for expanding fertilizer use. One is Brazil, which is not only raising land productivity but also steadily expanding the cultivated area. These two trends, together with the need to heavily fertilize nutrient-poor soils in both the cerrado and the Amazon basin, should continue the steady rise in fertilizer use in Brazil for the indefinite future. (The risks associated with this are discussed in Chapter 9.) 21

For the world as a whole, however, the era of rapidly growing fertilizer use is now history. In the many countries that already have effectively removed nutrient constraints on crop yields, applying more fertilizer has little effect on yields. Indeed, where fertilizer application exceeds crop needs, nutrient runoff can contaminate drinking water and feed algal blooms that lead to eutrophication and offshore dead zones. 22

Paralleling the tenfold increase in fertilizer use during the last half of the last century was the near tripling of irrigated area. (See Figure 4–3.) During the earlier part of this period, growth in irrigation came largely from the building of dams to store surface water and channel it onto the land through networks of gravity-fed surface canals. By the late 1960s, however, as the number of undeveloped dam sites diminished, farmers in countries like India and China were turning to underground water sources. Millions of irrigation wells were drilled during the remainder of the century. 23

Now the potential for building new dams is limited. So, too, is that for drilling more irrigation wells, simply because the pumping volume of existing wells is already approaching or exceeding the sustainable yield of aquifers in key agricultural regions.

Over half of the world’s irrigated land is in Asia, and most of that is in China and India. Some four fifths of China’s grain harvest comes from irrigated land. This includes virtually all the riceland and most of the wheatland, plus part of the cornland. In India, over half of the grain harvest comes from irrigated land. And in the United States, irrigated land accounts for one fifth of the grain harvest. 24

The growth in irrigation facilitated the growth in fertilizer use. Without irrigation in arid and semiarid regions, low soil moisture limits nutrient uptake and yields. When released of this constraint, plants can effectively use much more fertilizer. The availability of fertilizer makes investments in irrigation more profitable. It is this synergy between the growth in irrigation and fertilizer use that accounts for much of the world grain harvest growth over the last half-century or so. 25

The availability of fertilizer helped to offset the loss of nutrients associated with the steadily expanding one-way flow of farm products, and the nutrients they contained, from farms to distant cities and other countries. The United States, for example, selling up to 100 million tons of grain a year to other countries, exports 2–3 million tons of the nutrients essential for plant growth, including nitrogen, phosphorus, and potassium. The use of chemical fertilizers prevents the outflow of grain from draining the croplands of the U.S. Corn Belt of nutrients. 26

With irrigation as with fertilizer use, the growth worldwide has slowed dramatically over the last decade or so. Indeed, in some countries, such as Saudi Arabia and China, irrigated area is now shrinking. This is also true for parts of the United States, such as the southern Great Plains. In many parts of the world the need for water is simply outgrowing the sustainable supply. 27

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