Rice
- Its adaptation spreads from sea level to 3000m height in Nepal, from 49oN to 46o Crop requires relatively high temperature for optimum growth and development.
- Temperature requirement for rice production ranges from 20-370 The favorable temperature for physiological processes is 15-330C.
- Optimum temperatures required at different stages of rice crop growth are;
Germination |
20-35oC |
Seedling establishment |
25-30oC |
Tillering |
31oC |
Panicle initiation |
33oC |
Anthesis |
30-32oC |
Ripening |
20-25oC |
- A mean temperature of 220C is required during the growth period.
- A higher mean temperature greater than 330C would reduce the growth duration and accelerate flowering whereas average temperature less than 150C would cause a slow vegetative growth and plant fails to flower.
- Low temperature depresses germination, slows down the growth processes and delays the maturity.
- Rice yield is greatly reduced by the formation of sterile spikelet’s, which are induced by low temperatures. The period during which the low temperature is most critical is about ten to eleven days before heading occurs.
- When low temperatures do not occur during this critical period, sterility is generally not induced-even when temperature exceeds 350C during anthesis and lasts for more than 1 hour.
- In rice, problem is low temperature damage (10 to 210C). Low temperature in reproduction and ripening stages results in shattering of grains in many high yielding varieties.
- Optimum photoperiod for sensitive variety of rice is 10 hours.
- According to photoperiod sensitivity, rice cultivars can be classified as
Photoperiod sensitive variety: Traditional type, Pokhareli, Jumli masino
Weakly sensitive: Early variety like Radha-4, Heera
Non-sensitive: Modern varieties such as Durga and Khumal-4
- Low light intensity results in reduction of total photosynthesis.
- Shading makes the plant taller, shading during the first phase (transplanting to panicle initiation-44 days) reduces yield more than that at other stages through greater reduction in effective tiller and length and grains per panicle.
- There should be a monthly rainfall of 200 mm to grow lowland rice and 100 mm to grow upland rice, successfully.
- The feet of plant should remain submerged in water from the time of sprouting to the milk stage of the grain.
- At waxy ripeness, no standing water in the field is required.
- Stress during panicle development to early ripening is more harmful and irreversible than that at early or later stages.
- Prolonged stress during initial stage increases crop duration.