Maclean et al. - 2002 - Rice almanac source book for the most important e

Aerobic rice cropping is not an option in
semiarid to arid climates, nor on saline and acidsulfate
soils. Removal of a permanent water
layer and thereby reduced percolation could
result in soil degradation such as salinization,
alkalinization, and acidification. Water-saving
efforts under these conditions concentrate on the
replacement of long- and medium-duration
varieties by short-duration varieties and on good
water management (e.g., irrigation stops 2 weeks
before maturity).
In the Sahel, short duration has been a target
for introduction and breeding for some time. In
the mid-1990s, cultivar Sahel 108 was
introduced and quickly proved popular,
occupying one-third of the rice area of the
Senegal side of the Senegal River Valley in the
wet season and two-thirds in the dry season, and
up to a third of the area on the Mauritanian side
of the river in 1999. It thus saves at least 11
million m 3 of water use by plants; at 40%
irrigation efficiency, this amounts to 28 million
m 3 , or $400,000 in saved fuel costs for pumping.
The water-weed connection
One reason farmers keep rice fields continuously
flooded is to keep down weeds, which compete
less well with rice under such conditions. But if
flooding is reduced, other ways of controlling
weeds will be necessary.
Scientists are now examining the place of
weeds in the entire rice-growing system, with the
aim not simply of attacking and killing them by
one means or another, but of managing them in a
way that will not interfere unduly with rice
production. This involves studying the interaction
of such components as water, tillage
practices, and weeds, and incorporating in the
rice plant characteristics that increase
competitiveness with weeds, such as early vigor.
It also involves investigating naturally occurring
pathogens of weeds and how they might be used
to suppress weed growth.
By such means, scientists at CIAT, IRRI,
and WARDA are developing environmentally
sound integrated weed management systems that
they hope will prevent the kind of excessive
reliance on chemical herbicides that happened
with insecticides a decade or so ago. Meanwhile,
herbicides remain an important component of
integrated weed management and their use is
rising rapidly. At the same time, weed resistance
to them is increasing. Up to 15 major weed types
now show such resistance and strategies are
needed that minimize herbicide use and promote
the development of further resistance.
A new research initiative
So important is the water problem worldwide
that the Consultative Group on International
Agricultural Research (CGIAR)—a consortium
of donors supporting 16 international research
centers including CIAT, IRRI, and WARDA—
has mounted a water conservation campaign. The
International Water Management Institute and
several other CGIAR and national research
centers are investigating the effects of on-farm
water management on system performance
through a network called SWIM—Systemwide
Initiative on Water Management. The objective is
to enhance the productivity of water in an
environment of growing scarcity and
competition. The result is expected to include not
only ways to increase water productivity but also
the development of methods to measure water
productivity that will be widely adopted by
researchers and the building of research capacity
in water management. The main focus of SWIM
is a comprehensive assessment of the benefits,
costs, and future directions of irrigated
agriculture.
Adding protein, vitamin A, and
other micronutrients
Vitamin A is one of the most important nutrients
in maintaining life and health. Consequently,
dietary lack or deficiency of this vitamin leads to
severe clinical symptoms. Africa, Asia, and Latin
America and the Caribbean have areas where this
is a severe problem. Overall, around half a
million children become irreversibly blind each
year as a result of vitamin-A deficiency. A much
larger number of children develop other eye
problems—5 million children per year in
Southeast Asia alone. Worldwide, an estimated
124 million children are deficient in vitamin A to
some extent, and improved intake would prevent
1–2 million deaths each year of 1- to 4-year-old
children.
IRRI is joining an international research
endeavor to find out whether rice consumption
can help prevent this problem. The research has
been made possible by the development in
European laboratories of Golden Rice, a
genetically modified rice variety that contains
International issues 33