Vergara - 1976 - Physiological and morphological adaptability of ri

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Temperature and the chemical
kinetics of flooded soils
F. Ponnamperuma
SUMMARY
oil temperature is an impoitant factor determining the growth and yield of
rice in submerged soils. Apart from its direct influence on the physiology
of the roots and other submerged part. of the plants. soil temperature markedly
affects the nutrition of the rice plant through its effects on the chemical kinetics
of the soil.
Laboratory" and greenhouse studies on the chemical kinetics ofa total of 20
submerged soils maintained at l5‘. 25*‘. 35"’. and 45C or 38° ' 20C. 30°C. 15°
'
"
31° llPC. and 20°C revealed that the 35° and 33° " 20°C regimes produced
a rapid increase in pII of acid stiils. rapid and narrow‘ peaks of carbon
dioxide. volatile organic acids. reducing substances. and ferrous iron; and an
increased supply of anunonia and phosphate, compared with the other temperature
regimes. Temperatures below 25°C brought about a slow build-up of high
and persistent concentrations of carbon dioxide. volatile organic acids. ferrous
iron, and reducing substances, especially i11 the acid soils. A constant temperature
of 45°C leads to the production of high concentrations of reducing substances
and carbon dioxide.
INTRODUCTION
Growth and yield of rice was best under the 35°C and 38° " 20°C regimes,
and poorest below 20°C and at 45°C. The adverse effects of low temperature
were more scvcrc 011 acid soils than 011 neutral soils.
The temperature regimes in flooded rice soils vary wldClfy’. In the temperate
zone, soil temperature may range from 15°C at planting to 40°C in late summer.
In the subtropics, for the second crop, soil temperature declines as the crop
matures. The two main temperature regimes. in the tropics are fairly constant
temperatures of about 30°C at sea level and about 20°C in the highlands.
Rice physiologists have studied extensively‘ the effects of temperature on germination.
growth. flowering, grain fo1mation_ and the uptake of nutrients.
chiefly from culture solutions (Matsuda, 1930; Takahashi ct al.. 1955; Sasaki
and Fukuju, 1958; Aimi and Sawamura. I959; Chapman and Peterson, 1962;
and Takcshima, 1965). Others have reported thc effects of temperature on the
uptake of water and nutrients from submerged soils (Takeshima. I964; Suzuki
F. N. Ponnamperuma. Soil Chemistry Department. Intemational Rice Research Institute (IRRI). Los
Bafios. Laguna, Philippines.