Agriculture Reference
In-Depth Information
temperature is also a major factor in affecting the availability of
zinc. Larger corrective applications of zinc are required in cool
seasons. Phosphorus-induced zinc defi ciencies do not appear to
be a signifi cant problem in rice. Cold soil reduced phosphorus
uptake, as well as, most other chemical and biological activities
in the soil. Optimum soil temperature for potassium uptake is
60-80°F. Potassium uptake is reduced at low soil temperature.
Low temperature retards the respiratory rate and reduces
nutrient uptake.
Takahashi et al. (1954) showed that the depression of mineral
absorption came in the order magnesium > manganese > silicon
> calcium > nitrogen > phosphorus. The uptake of potassium
seemed to be enhanced by low temperature. Fujiwara and
Ishida (1963) found that the absorption of manganese was
greatly enhanced by low temperature but drop below normal
when low temperature treatment was extended. Fujiwara and
Ishida (1963) reported that the inhibition of absorption are
equally severe at 17°C for phosphorus, potassium, nitrogen,
iron, silicon, calcium and magnesium for the fi rst 2 weeks
after transplantation. At tillering stage, severe inhibition
occurred for phosphorus, potassium and calcium at 17°C, the
absorption of manganese was accelerated. Low temperature
during early growth stages causes yellowing of leaves and
stunting. The limited supply of photosynthates and nutrient
elements coupled with the direct effect of low temperature on
the respiration rate in growing parts and the reduced effi ciency,
all combine to reduce the growth of the growing organs (Murty
1980). The translocation of the carbohydrates to the growing
seedling is also impaired (Fig. 19).
CO
2
assimilation underpins plant productivity and is
therefore central to any analysis of the response of plants to a
change in temperature. Photosynthetic characteristics in rice
leaves after treatment with low temperature (15°C) and high
