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

terraces of the northern Philippines are situated
in one of the wettest rice-growing regions of the
world, with an average annual rainfall of 3,530
mm.
As a further complication, when rain comes
in Asia it usually arrives in torrents over a short
period, during a single monsoon that lasts from 4
to 6 mo. The rest of the year is almost dry. As a
result, much of the runoff simply flows into the
ocean as waste, at the same time eroding the
uplands, sometimes catastrophically. Furthermore,
the monsoon is often erratic, so that, in
many countries, floods and seasonal water
shortages occur concurrently.
Environmental costs of increased
rice production
Water was a critical input to the Green
Revolution, through irrigation, flood control, and
drainage, and it has contributed most to the
growth in rice production for the past 30 years.
But this expansion has occurred at a cost to the
environment: a proportion of the chemicals
applied as fertilizer and for pest and weed
control pollutes rivers and lakes through runoff
or groundwater through leaching.
In some upland areas, intensive agricultural
practices, coupled with deforestation, have
resulted in high rates of soil erosion and degradation
of both land and water resources in lowlands
below. The effects can reach as far as coastal
waters, with a consequent effect on riverine and
marine life.
Another problem involves long-standing
surface water, which causes waterlogging, makes
the land unproductive, and leaves soils salty as
the water evaporates. In India, about 6 million ha
of irrigated land are known to be affected by
waterlogging. Nearly 10% of Pakistan’s irrigated
13.5 million ha is estimated to be affected by
salinity, and northwestern India and northeastern
China are similarly degraded.
Overexploitation of tube and shallow wells
also presents problems. This is the case in large
areas of India, Pakistan, and Bangladesh. The
practice causes shortages of drinking water and
pollution when aquifers are recharged with
irrigation water contaminated with chemicals.
Capital costs of irrigation systems have
recently soared. In Sri Lanka, it cost almost three
times as much per hectare of land to set up an
irrigation system in the 1990s as it did in the
1960s, twice as much in India and Indonesia, and
nearly 50% more in the Philippines and Thailand.
At the same time, market prices for rice
have plummeted by nearly 40% over the past 30
years, while political pressure from
environmental groups against large-scale projects
is mounting.
What this will mean for future rice
production is that it will depend heavily on the
development of water-efficient measures
producing more rice per unit of water input. The
trend now is to develop management policies for
the efficient operation of irrigation systems;
technologies that reduce water consumption;
changes in the rice plant itself and the ways in
which it is grown, so as to use water more
efficiently; and to provide economic incentives
to farmers to reduce water losses.
Aerobic rice
One way to save water is to make a rice plant
that needs less of it. IRRI scientists are working
on creating a high-yielding tropical rice plant
that grows on dry but irrigated land instead of in
flooded paddies, calling it “aerobic rice.” An
Aerobic Rice Working Group has been formed,
consisting of plant breeders, physiologists, and
water and soil scientists, to address the many
difficulties of taking the plant out of its natural
environment and growing it as a dryland crop
like maize. Some upland rice varieties already
withstand drought but they are low-yielding and
do not respond to fertilizers.
A first step has been testing aerobic
varieties, already used commercially in Brazil
and experimentally in China, in tropical
conditions. In Brazil, the aerobic rice crops are
rotated with other crops. However, when the
plants are used as a single crop, as on most Asian
farms, yields fall dramatically after the first few
seasons, a phenomenon called “yield collapse.”
This is the major problem that the research is
now addressing.
Dry seeding—which can avoid the waste of
400–600 mm of rainfall—is assuming an
important role in rice production in rainfed areas.
The early harvest of dry-seeded rice can allow
planting of a second crop, which makes use of
rainwater that arrives later in the season. This
practice also reduces risk of drought where the
rainy season is short, and because dry-seeded
cultivars can generate more roots.
32 Rice almanac