MSc 1996

It is known that there exists varietal differences in tolerance to
nutrient deficiency conditions among rice cultivars. The sandy soils of
Onattukara region is inherently deficient in K which resulted in a higher
POP recommendation for rice in terms of K application. So to exploit
the varietal differences of rice in deficiency tolerance of K, a field
experiment was undertaken to screen 48 rice cultivars belonging to tall
indicas and dwarf high yielding groups of varying growth durations.
The experiment was laid in 384 microplots in "Group Balanced. Block
in Split Plot Design" with four K levels and two replications. The
various growth and yield attributes and yield were studied with a view
to locate varieties which could produce similar yields even at lower
levels of K.
The results indicated that in general the varietal influences on
most of the growth characters in all the four groups were profound.
Moreover positive and significant effect of K doses were observed.
However LAI showed no variation with differing levels of K.
Differential response of varieties to varying K doses as manifested by
root spread was considerable only in medium duration varieties while

an appreciable difference was noticed in the root spread in all the
groups. Root length, thin root-thick root ratio and root CEC appeared
to be varietal characters which increased with increasing levels of K.
The plant nitrogen content at varying levels of K was more of
a varietal character. On the contrary, long duration varieties exhibited
significant variation in P content with differing K levels at all critical
stages of crop growth. Both K levels and genetic variability of the
varieties were equally important in deciding the K content in plants and
the response to added K was of a higher magnitude.
All but long duration varieties responded positively and
significantly to K in terms of productive tiller formation and generally
tall indicas produced relatively longer panicles than dwarf varieties.
Higher levels of K also led to the production of heavier grains. Yield
increases over control was comparatively higher in tall short duration
varieties than. any other varieties for higher levels of K. Differential
response of K was highly pronounced in tall short duration varieties
with Ptb23, Ptb29, Cul 7005-6-1, Cul 7004-3-1, and Cul 7006-2-1 giving
comparable yields at 22.5 kg K20 ha-1 as that of the POP
recommendation. However as this experiment was done in microplots
the final recommendation of varieties tolerant to K deficiency could be
done only after extensive studies in large plots and in farmers' fields
during various seasons.