Vergara - 1976 - Physiological and morphological adaptability of ri

509
Nitrogen response of lowland and
upland rice in relation to tropical
environmental conditions
S. K. De Datta and J. Malabuyoc
SUMMARY
the tropics. rainfall is the most limiting thctor alike-ting nitrogen response of
Inrainfed rice. ln irrigated rice. nitrogen response is primarily determined by
solar energy levels during the reproductive and ripening stages. Solar energy
levels being higher during the dry season. nitrogen response is higher than in the
wet season. provided no other adverse tactors such as poor moisture supply‘.
poo!‘ soils. insects. diseases. and weeds would limit crop grotflh. In any sermon.
varieties with good plant tvpe give higher nitrogen response than varieties with
poor plant type ln lowland rice. inigated or rainfed. nitrogen response at Tami
level is largely detennined by moisture supply, soils. weeds. insects. and diseases.
As a result. differential responses of improved rice varieties to solar energy are
often less pronounced in tarniers‘ fields than in the experiment stations.
Upland rice is grown entirely as tainted in the cloudy monsoon season. Therefore.
nitrogen response is largely detemiined by the amount and distribution
of rainfall. Solar energy appears to be less critical than the moisture supply from
rain for obtaining high yields and nitrogen response. However. as with lowland
rice. nitrogen response of improved varieties is higher than that of the varieties
bred or selected for upland rice in the past in various countries Even under
good moisture supply". nitrogen response of upland rise is limited by management
factors. particularly weed control.
In the tropics. it is more critical now to maximize nitrogen response in rice.
upland or lowland. since both availability and prices are becoming less lhvorable
than in the past. Therefore, all factors, climatic. varietal. and management.
should be considered together in evaluating the nitrogen response of rice.
INTRODUC TION
Of the various climatic factors affecting nitrogen rcsponsc of tropical ricc,
moisture supply and solar energy arc particularly significant. Because of the
farmer's dependence upon rainfall to meet Water needs. without irrigation
he must grow his crops under conditions of high moisture variability‘ and low
sunlight intensity‘ during the rainy season. The amount of rainfall received
during the wet season. provided it is uniformly distributed. should be adequate
S. K. De Darla. J. .“i-1Glflblt_1‘()0'- Agronomy Department. lntemational Rice Research Institute (IRRI).
Los Bafios. Laguna. Philippines.