32 The Global Food System
Farmers themselves recognize the value of mixtures. In Indonesia, farmers in
rainfed conditions plant a greater mix of crop combinations during the more risky
seasons (Castillo, 1992). In the dry season, they plant 42 combinations; in the
uncertain middle season, they use 25; and in the rainy season, they plant just 7.
The author of a recent comprehensive review of intercropping, John Vandermeer,
has put it: ‘In personal conversation with [farmers] in southern Mexico, Costa
Rica and Nicaragua, I have frequently ... been told that two crops make a good
combination because one is taller than the other and “fits in” to the spaces where
the other does not, or that the root systems go to different depths and thus use
nutrients from different parts of the soil.’ Such popular knowledge is common.
It is, however, impossible to say categorically whether a mixture will result in
better yields than the monocropped alternatives, except perhaps for legume–non-
legume mixtures (Trenbath, 1976; Willey, 1979; Vandermeer, 1989). Much
depends upon the local conditions and characteristics of the crops themselves. Pest
attack is frequently reduced in intercrops, because of a variety of factors (Risch et
al, 1983). Host plants are more widely spread and so harder to find; one species
may trap a pest; or one species may repel the pest; and/or predators may be
attracted. Weeds are also more likely to be suppressed by mixtures.
Recent surveys of non-irrigated rice systems in Cambodia, Indonesia, Laos,
Madagascar, Myanmar, Nepal, Philippines and Thailand have found that farmers
manage their highly diverse conditions with different land use strategies (Fujisaka,
1990, 1991; Fujisaka et al, 1992). Farmers described different combinations of
landscape position, soil type, hydrology, and flood and drought risk, and showed
how they matched these to different combinations of rice varieties and manage-
ment practices. In upland Laos, for example, farmers distinguished 20 different
types of soil. Each grew up to four varieties of rice, with 29 varieties grown in the
two regions of Luang Prabang and Oudomasay. But these mixes are not static.
Farmers are continually experimenting with new varieties or readopting old or
existing ones. In Bukidnon, Philippines, farmers were cultivating 18 varieties, hav-
ing dropped another six in recent years.
In Myanmar, 52 different varieties of rice were encountered in rainfed uplands
and lowlands, and in deepwater conditions. Each farmer does not seek to maxi-
mize yield, nor do they have one preferred variety. They grow up to six varieties
each, with a range of different taste, colour, pest resistance, growth pattern, dura-
tion, flood/drought tolerance, milling recovery and market price qualities
(Table 1.5).
The decline under modernization
It is only recently that fields monocropped to single species and varieties have
become common. The introduction of modern varieties and breeds has almost
always displaced traditional varieties and breeds. During the 20th century, some
75 per cent of the genetic diversity of agricultural crops has been lost. Only about
150 plant species are now cultivated, of which just three supply almost 60 per cent