Vergara - 1976 - Physiological and morphological adaptability of ri

GEOGRJIPHH’ AND (jLlh-DYTE OF RICE 37
In mid-l974 rice carry-over from the previous years production totalled
450.000 tons in the USA and about 3.5 million tons in India. Supplies in Thailand
and Burma ivere modest and the only other supply. in Japan. was of shortgrain
rice. not a preferred variety in most tropical markets. At best the total
world cany-over was no more than 6 million tons of rice. only 3 1/3 percent
of world production.
On the surface 6 million tons of rice is a very“ impressive volume, a bit less than
thc 1966 carry-over. but almost thc same as the world stock in 1971. But how
much is 6 million tons when viewed from the perspective of world demand‘? Just
for a moment let us suppose that India was to undergo serious production
problems late in 1974 or in 1975. Certainly" it is possible that rice production
could fall from the high level of 43.5 million tons achieved in 1973 to the more
modest figure of 37.5 million tons produced in 1971. Such a decline is conceivable
given a shortage of nitrogenous fertilizers and a very poor monsoon season.
The WOfld stock is barely sufficient to make up this difference and to ward off
serious famine providing that shipping. storage. and distribution facilities are
readily available. If such a shortage were to develop. the world stock would be
totally depleted and the volume of exports to other areas ivould depend completely
on output from the current crop. There would no longer be a cushion of
reserves to meet emergencies should they develop in other rice-consuming
regions.
PHYSICAL CONSIDERATIONS
Let us now turn our attention to the physical geography ofrice-producing regions
and look in particular at climate. The first seemingly natural question appears to
be. “What is a rice climate?" A search of the literature reveals many interesting
insights into the question. We learn for example that rice is "a crop suited to the
wet tropics" or that "the highest yields are obtained in countries enioyiing a subtropical
or ivarm-temperate climate.“ Such statements are so general as to have
little meaning. Other sources tell us that rice "thrives over a wide range ofconditions
within about 45 latitude north and 40 south of the equator" or that
“paddy crops may be grown from sea level to about 10.000 feet in the appropriate
latitude."
More detailed analysis rebeals a number of additional constraints variously
reported by the different authors. A point made by almost all authors is that
high temperatures and a great deal of sunshine are needed. There is almost
universal agreement that high water availability is the most critical requirement.
and that the magnitude of this requirement is a function of the local evapotranspiration
rate combined with seepage losses and percolation through the soil.
Most authors agree that water is needed over a long growing season (120 days to
175 day's), but that ideally the ripening and harvest periods should be dry. wann,
and sunny. Total water need is most commonly stated as being between two and
{W0 and one-half times the pan evaporation or somewhere from 1 to 2 meters
per crop.