304 Agricultural Revolutions and Change
without fertilizer they sometimes did worse on poor soils.^34 Not surprisingly, aver-
age rates of application of nitrogen fertilizers, mostly ammonium sulphate and
urea, doubled and redoubled over a very short period (Figure 13.9).
Because the new varieties were more exacting in their requirements, good irri-
gation, by providing a controlled environment for growth, became crucial. Most
developing countries have both a dry and a wet growing season. Potentially, dry-
season yields are 50–100 per cent greater than in the wet, but the lack of rainfall
in the dry season and the high evapotranspiration rates resulting from absence of
cloud cover make the crops liable to water stress. Without adequate irrigation,
yields tend to be low and variable, whatever the level of fertilizer application. With
irrigation and heavy fertilizer application, some of the highest cereal yields in the
world have been attained. In south and southeast Asia the irrigated area grew from
some 40 million hectares to over 65 million hectares between 1960 and 1980, a
growth rate of 2·2 per cent per annum. By 1980 one-third of the rice area was
irrigated, producing a rapid increase in the dry-season rice crop.
Just how much of the increased cereal production has been due to the availa-
bility of the new varieties, how much to increased fertilizer use and how much to
the growth of irrigation is a matter of argument. An analysis of the eight countries
(Bangladesh, Burma, China, India, Indonesia, Philippines, Sri Lanka and Thai-
land) responsible for 85 per cent of the Asian rice crop suggested the three factors
had a roughly equal contribution. Of the extra 117 million tons produced between
1965 and 1980, 27 million tons were attributable to the new varieties, 29 million
tons to increased fertilizer use and 34 million tons to irrigation.^35
Inevitably, the need to provide high levels of fertilizer and controlled, irri-
gated environments meant that some locations were favoured over others.
Source: FAO, 1994 [Fertilizer data diskettes], Rome, Food and Agriculture Organization
Figure 13.9 The growth of fertilizer use in the developing countries