Vergara - 1976 - Physiological and morphological adaptability of ri

oration-win‘ AND (ILIAIATE or RICE
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Not onlv must man provide water in such environments but he must also
provide drainage to prevent the accumulation of salts in the surface layers of
the soil. Without adequate drainage the loss of productive capacity" can be very
rapid. as Pakistan discovered during the 1950's and 1960's. The provision of
drainage is still another man-made modification of the environment which
requires additional energy inputs.
If man is Willing to invest suficient energy. then the hot desert areas are capable
of providing the highest yields per unit of surface obtained from any area
in the world. High levels of output can be maintained year after year with little
variation.
This environment is not favorable for the pathogens of plant diseases and does
not encourage the development of insect pests. Solar radiation is at very high
levels and shows little variation from year to year. Clearly. the limiting factor is
the availability of the energy needed to provide irrigation and drainage. As long
as the food energy derived from the crop exceeds the volume and value ofenergy
inputs. then hot desert areas Will remain excellent producers.
Some producing areas on polar margins of the rice World have shown remarkable
expansion of output in recent decades. Hokkaldo and Manchuria are
examples. Here the chief environmental or climatic problems are short growing
seasons and low temperatures. especially‘ early in the season. Again. man
through his technological skills and the application of energy derived from fossil
fuels has been able to modify the environment so that rice can be produced.
Breeding programs have developed varieties with a shorter growing season. and
electric heating cables buried in the soil of the nursery beds have provided increased
soil temperatures and protection for the young plants against temperatures
too cool for normal plant development. With this use of stored energy and
the provision of supplemental irrigation during the long hot summer day's. Hokkaido
has been converted to an excellent rice-producing area with yields per
hectare among the highest in all of Japan.
For optimum growth the rice plant needs several climatic conditions. lt must
have high temperatures. a moderately long growing season. sufficient solar radiation,
a large volume of water evenly distributed through a major portion of
the growing season, and a ripening period which is relatively dry". The ideal rice
climate must provide all of these conditions and, in a perfect ‘world, should
provide these parameters consistently year after year. Llnfortunately for man.
the perfect rice climate does not exist. On the other hand, man has the capability
to modify any or all of the existing parameters to produce artificially an
optimum climate at any location he chooses. The further removed from optimum
conditions man chooses to produce rice. the greater must be the climatic
modification and the greater must be maifs use of energy t0 achieve the desired
results.
PERCEPTION OF CLIMATE
The world map of rice production can be very’ crudely divided into three types of