NCPA - National Center for Policy Analysis

Monoculture And The Risk Of Crop Failure

April 10, 2002

By cultivating a small number of crops over large areas, farmers can dramatically increase profitability. This is why monoculture, cultivation of a single crop over a large area, is increasingly common in agriculture.

But despite its short-run advantages, monoculture may also impose a long-term risk of crop failure. Economist Martin Weitzman of Harvard University says the vulnerability of a crop to a pathogen is highest when the amount of the plant in cultivation is small -- or when it is very large.

The vulnerability of a small crop is obvious, but that of a widespread crop is less so.

In the Quarterly Journal of Economics, Weitzman explains why it may in effect be too much of a good thing:

  • Large, homogeneous crops enable parasites -- bacteria, viruses, fungi and insects --- to specialize on one specific host, increasing the chance they will mutate into a more pathogenic form.
  • Farmers tend to choose the same crop cultivated by neighboring farms because of efficiency gains (e.g. in spraying and seed storage); but this makes it easier for a disease to spread -- for example, food and mouth disease spreads more easily where neighboring farms raise the same species.
  • Using a complex statistical model, Weitzman shows that once the size of a crop passes a certain threshold, crop extinction can be very abrupt.

Thus the author argues for diversity in the world's crops, even if this entails lower yields, as matter of food security.

Source: "The Risk of Catastrophic Crop Failure," Economic Intuition, Summer 2001; based on Martin L. Weitzman, "Economic Profitability Versus Ecological Entropy," Quarterly Journal of Economics, February 2000.


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