Vergara - 1976 - Physiological and morphological adaptability of ri

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Climatic influence on yield
and yield components of lowland
rice in the tropics
S. Yoshida and F. T. Parao
SUMMARY
n an experimental field at Los liafios. Philippines. when an improved early-
Iniaturing variety xi-"as grown throughout the year with good cultural practices,
grain yields were highly correlated positively with average daily solar radiation
and negatively with average daily‘ mean temperature during the reproductive
stage. i.e_ the 25-day period before flowering.
Analysis of yield components indicated that spikelct number per square meter
alone explained 60% of yield variation while the combination of all the yield comporlents
accounted for 81% of yicld variation. filled grain percentage and grain
weight together accounted for 21 “*0. These results. combined with those obtained
from CO; enrichment experiments. showed that sink size WtlS more limiting to
grain yield at Los Bafios than was grain filling.
Controlled-environment and field studies demonstrated that variations in
temperature and solar radiation within ranges commonly encountered during
the vegetative stage do not have any overall effects on yield and yield coinponents.
Relatively low temperature and high solar radiation during the reproductive
stage have remarkable effects on increasing spikelet number and hence
grain yield. Solar radiation during the ripening period influences grain lilling.
An examination of yield and yield components data collected from various
locations in the tropics seem to indicate whether weather conditions before
flowering or after have a greater effect on yield is location- or season-specific.
A 3-year average annual production from four crops a year was 23.7 tflia.
Hence, total dry-matter production ivould be estimated at about 35 t- ha 1- yr‘.
On a yield-per-crtip basis, the tropical environment may not necessarily be more
productive than the temperate region. but it has a greater potential in terms
of annual production.
CLIMATIC INFLUENCE ON CROP YIELD
Climatic factors such as temperature. solar radiation, and rainfall influence
growth and hence yield of rice in two ways. Directly, they affect the physiological
processes involved in grain production. such as vegetative growth. formation of
storage organs. and grain filling. Indirectly. they affect grain yield through
incidence tifdiseases and insects.
S. Yoshida. F. T. Parao. Plant Physiology Department. International Rice Research Institute (IRRI),
Los Bafios, Laguna. Philippines.