Book review: Exploding the myths of soil erosion

Published August 1, 2001

The generally accepted opinion is that a large percentage of the world’s agricultural land is degraded and is being further degraded year by year. The World Map of the Status of Human-Induced Soil Degradation, produced by the United Nations Environment Program in the late 1980s, is a major source of that opinion.

In Shifting Ground, Peter Lindert argues–persuasively in my opinion–that the basis for the conclusion that a large percentage of the world’s agricultural land is degraded as a result of human action is wholly inadequate. The evidence used to reach this conclusion is not derived from historical comparisons of the status of agricultural lands, he notes, but on a description of lands at a particular moment in time. As Lindert writes, “It tries to measure changes over time in the absence of data over time” (page 21).

Good data are available

Lindert (professor of economics and director of the Agricultural History Center at the University of California, Davis) utilizes data from soil surveys in China and Indonesia. These data–from the world’s largest and fourth-largest countries (in terms of population)–have been available for decades. These surveys cover a period of approximately half a century, from the 1930s to the 1980s.

The surveys provide measures of soil characteristics for a given location at a given time. While the surveys are not identical in all respects over time, there are many common elements: measures of the major nutrients, of organic matter, alkalinity, acidity, and the depth of the top soil.

Such surveys exist in other countries, including the United States, but apparently only Lindert has used them to provide a realistic picture of the changes in soils over time. Given the availability of such data, it is surprising they have not been used before to understand what has happened to the quality of the world’s soils.

The reason may be that it is an enormous amount of work to effectively utilize the hundreds–thousands, probably–of these surveys. So far, Lindert has been the only one willing to make the required investment of time.

Erosion happens

That erosion exists cannot be questioned. After all, the Yellow River didn’t get its name by accident. But in much of the discussion of erosion, as well as other aspects of soil degradation, it is seldom asked whether the erosion is human induced–it tends to be merely assumed that it is.

In addition, when and where there is erosion, little or no evidence is provided as to whether it occurs on farmland. Lindert directly addresses the issue of whether the erosion has taken a serious toll on the farmlands of two countries. As noted below, he finds no evidence that the depth of the topsoil has declined over a period of half a century in these two countries.

One can hope that future estimates of soil degradation, including the extent of soil erosion, will utilize the real evidence that is available rather than speculating of the basis of models not grounded in historical data.

Farming has not hurt soil quality in China

Based on the comparisons of the soil surveys in China, Lindert concludes there have been positive and negative changes affecting the quality and quantity of farmland. The negative factors have been declines in the nitrogen and organic matter in the soils, while potassium and potash contents have increased. The decline in nitrogen content of the soil seems to have little or no negative effect on yield, however, since nitrogen can be and is added as fertilizer.

Perhaps the most striking conclusion is that the depth of the topsoil has not diminished–erosion has not taken a toll on China’s soils. And the quantity of farmland has apparently increased over the past half-century, as recently confirmed by the Chinese government, rather than decreasing significantly as has been often claimed by Lester Brown, Vaclav Smil, and others.

Lindert summarizes what has happened to soil quality in China: “The most reliable . . . basic inference is that the overall soil quality did not decline between the 1950s and the 1980s” (page 145). In fact, some of his estimates indicate a modest increase in soil quality. Thus in a period of rapid change–the creation of the communes, the period of the Great Famine, the Cultural Revolution, and the reforms of the late 1970s and early 1980s when the communes were abolished and the household responsibility system emerged–the evidence is very strong that the quality of the soil was not diminished.

Similar findings for Indonesia

In addition, Lindert finds no evidence that erosion of agricultural land in Indonesia was a problem. This conclusion is based on two types of evidence: the absence of a decline in the content of major nutrients in the soil, and the adjustment of the depth of topsoil data to account for certain problems in the data for the early years.

His overall estimate is that the average soil chemical quality declined by 4 to nearly 6 percent. This decline was due primarily to bringing new lands into cultivation in the outlying islands–the soil quality index for the established agricultural areas in Java and Madura may have increased by as much as 10 percent. The area under cultivation more than doubled between 1940 and 1990. If land is adjusted to the Javanese quality level and adjustment is made for the small decline in average quality, the increase in quality-adjusted land under cultivation during this period was more than 75 percent.

Farmers make good and stewards

To summarize the results presented in this very important book, Lindert shows that for two of the most populous countries in the world, farm people have taken very good care of their land. Yes, erosion exists–but careful analysis is required to determine whether it is human induced and whether it affects agricultural land.

Lindert’s careful analysis supports two important conclusions, though these conclusions are not stated explicitly by him. His work confirms that “farmers are as smart as the rest of us” and that “farm people of China and Indonesia have been good stewards of their land.”

Studies similar to this one should be made for other countries or areas for which soil surveys exist over extended periods of time to determine whether farmers elsewhere have been good stewards of their land. My expectation is that they have been. I do not believe the experiences in China and Indonesia were unique.

D. Gale Johnson is the Eliakim Hastings Moore Distinguished Service Professor of Economics Emeritus at the University of Chicago. He is the author of World Agriculture in Disarray, revised edition 1991, and “Agricultural Adjustment in China: Problems and Prospects,” Population and Development Review, Vol. 26, No. 2, June 2000.

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