Mineral Fertilizer Use and the Environment International Fertilizer Industry Association United Nations Environment Programme

particularly in Sub-Saharan Africa and South
America, but three quarters of this land suffers
from soil and terrain constraints. Much is under
forest. The amount of additional fertile, well-
watered, non-erodable, unforested land that can
be brought into agricultural production at low
cost is very limited. Somewhat more land could
be brought into production with significant
investment in reclamation or irrigation, but the
rate of increase of irrigation is slowing because
water is another increasingly scarce resource.
In any case, over the last 50 years, the
increase in agricultural production has been
achieved mainly by increasing crop yields - the
overall agricultural area has expanded relatively
little. In 1960, the global area under arable and
permanent crops was about 1.4 billion ha. By
1990, this had expanded by just 3.5% to 1.48
billion ha. But the world’s farmers were able to
grow about one billion tons more cereals in 1990
compared with 1960. According to FAO, four-
fifths of agricultural growth in developing
countries is likely to come from intensification
(increased yields, multiple cropping and shorter
fallows.
15.1.4. Water
Agricultural irrigation uses over 70% of the
world’s supplies of developed water and in the
drier farming regions crop production is heavily
dependent on irrigation practice. Agriculture is
facing increased competition for limited water
resources. During the next three decades, there
will be an increasing number of water-deficit
countries and regions including not only West
Asia and North Africa but also some of the major
agricultural producing regions of the world such
as the Indian Punjab and the central plain of
China. The efficiency of utilization of irrigation
water is often low and around 50% of the
increase in demand for water could be met by
increasing the effectiveness of irrigation
(D. Seckler et al., 1998). It is therefore extremely
important to improve the efficiency of water use
and it is established that something approaching
the economic maximum of plant material ensures
high water use efficiency. This objective will be
achieved only with a well nourished plant. Other
experiments have shown that the return from
nitrogen is much increased by irrigation (G.
Cooke., 1966, pages 245 -246, J.C. Ignazi., 1992
and J.S.P. Yadav et al., 1998). The dependence of
water use efficiency on plant nutrient supply is
reviewed by J.G. Davis, 1994. In fact any input
factor that increases economic yield will improve
water use efficiency (FAO, 1984).