Vergara - 1976 - Physiological and morphological adaptability of ri

526 censure AND RICE
disease- and insect-free situation. Rice is grown once in 3 to 4 years in rotation
with pastures. and oftentimes grain yield response to nitrogen is negligible compared
with that recorded in Japan or in the United States. Pests and disease
problems are very serious in Japan compared with those in southern Australia
or in the Llnited States.
In the tropical monsoon countries, the average farm size is about 3 hectares
and irrigation facilities and cultural practices. particularly fertilizer application,
insect. disease. and weed control. are far less intensive than those in Japan. As
a result. the nitrogen response of rice in fanners" fields is considerably lower in
the Asian tropics than in temperate Japan, although solar energy levels during
ripening period in both regions are similar. Nitrogen response under experimental
conditions (De Datta et al., 1968) and yield potential of rice in the
tropics are. hOWIH-‘Ct’, similar to those in Japan (Yoshida and Cock, 1971).
These and other data clearly demonstrate the seasonal effects of solar energy
and moisture level on the nitrogen response of ricc. However. there arc lcss differences
in N response between dry and wet seasons at farm levels in the tropics
than in the experiment stations. This can be explained by poor soil. poor water
supply, and weeds, insects. and diseases, all of which constrain yield. Some of
these factors can be controlled at farm levels if sufficient incentive is proitided to
the farmers in the fonn of credit to purchase inputs. One factor, adequate and
timely ivater supply, is not easily provided by individual farmers.
NITROGEN RESPONSE IN IIPLAND RICE
Effect of plant type, moisture supply and solar energy
Since upland rice is grown entirely ivith rainwater, the amount and distribution
of rainfall are of considerable importance. Water is more critical for growing
upland rice because raimvater cannot be stored by bunds as it can be in growing
rainfed lowland rice. The lower the rainfall during the growing season. the lower
the grain yield of upland rice. Hoxvever, results from several experiments at the
International Rice Research Institute and other experiment stations, as well as
in fanners" fields. demonstrate that even in an area receiving high annual rainfall
(2,000 mm), rain distribution still exerts a major influence on grain yield of
upland rice (Jana and De Datta, 1971; De Datta ct al., l9T4).
In monsoon Asia. the amount of rain and duration of the rainy season vary
not only between countries but also in different regions within a country. For
example. upland rice is grown under heavy rains in eastern India, particularly’
in the states of Assam and West Bengal. and in the coastal area in Kcrala
as well as in the low" rainfall area in Madhya Pradesh. In eastern Uttar Pradesh.
the growing season is extremely short and rainfall is highly‘ variable. The upland
areas in Bangladesh are similar to the easteni Indian states, particularly West
Bengal. The rainfall pattern in Indonesia is as diverse as in India.
In the Philippines, the average yields of upland rice are closely associated
with climatic zones, particularly the rainfall pattern (De Datta and Vcrgara,
1975).