Vergara - 1976 - Physiological and morphological adaptability of ri

258 CLIMATE arm RICE
mum
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It
Lulstuno clay I/ R‘
, \
v—e m» 5| - e ‘c
r--4 20'C
¢-¢ 30's
----o 3-» no‘:
'7. Influence of temperature on the kinetics of water-stumble Fc~ .
concentrations of water-soluble Fe“ were short-lived in the 38% 20°C regime
and the 30°C regime. This is good for rice because excess Fee is toxic to rice.
Low temperature retarded but did not prevent the build-up of high l"'e1'
concentrations. The concentrations were highest and most persistent at 15°C
and 20°C. The subsequent increase in temperature in the l5°a 3l°a 18°C regime
hastened the decrease in Fe” concentration. The temperature effects were least
in Maahas clay (pH : 6.6; organic matter: 2.0 %; free Fe: 1.6%).
Cho and Ponnarnperuma (I971) have suggested that excess water-soluble
l’ e1" may be one cause of cold temperature injury in submerged. acid rice soils.
Reduction of manganese
The reduction of manganese followed patterns similar to those of iron (IRRI.
unpublished). In all soils. except Luisiana clay. reduction was fastest at 45°C
and slowest at 15°C. In Luisiana clay it was slower at 45°C than at 25° and 35°C.
In Pila clay loam. temperature had little effect, for almost all the manganese
was reduced within I uteek of submergence at all temperatures.
It is remarkable that Pila clay loam. which gave the fastest rates for denitrifieation.
reduction ol‘ iron. and the reduction ol‘ manganese. also showed the
smallest response to temperature changes.
Water-soluble Mn“
The kinetic patterns of water-soluble Mn“ were similar to those of Fe”, but
low temperature retardation was less severe and the differences among 15°.
25°, 35°. and 45°C were less marked (IRRI. I967, I968“).
The concentrations of \\’3l€l'-SOltlblB Mnl“ in the range encountered (1 to 8O
ppm) may not be injurious to rice plants