Monoculture and the risk of crop failure

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 specialise on one specific host, increasing the chance they will mutate into a more pathogenic form.

  • Farmers tend to choose the same crop cultivated by neighbouring farms because of efficiency gains (e.g. in spraying and seed storage); but this makes it easier for a disease to spread – for example, foot and mouth disease spreads more easily where neighbouring 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.

    For more Economic Intuition research summaries
    For more on Agricultural Monoculture

    RSA Note:
    According to a geneticist consulted by the FMF, seed companies and farmers are very well aware of the danger. Seed companies therefore ensure the availability of a large number of different varieties of seed of any particular plant type, and the different varieties have a range of qualities that enable them to resist various types of diseases and pests.
    Eustace Davie, Director, FMF.

    FMF Policy Bulletin\17 April 2002
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