Climatic Requirement:
A) Solar Radiation :
- Rice is short day plant requiring about photoperiod of about 10 hours.
- Local landraces are sensitive to photoperiodism . Examples are Pokhreli masino , kali namak , Jumli masino.
- However modern varieties are mostly day neutral , slightly sensitive to photoperiodism. Examples are CH-45 , chaite 2 , Chaite-4 , laxmi.
B) Tempertature :
- Temperature range frr rice prosuction is 20-25 0
- Optimum temperature is about 250
C) Rainfall :
- Rice is semi-aquatic plant.
- Optimum total rainfall is 1000-1250 mm.
- In Nepal , national GDP depends upon productivity of rice and which depends upon the monsoon and its distribution throughout the growth period.
D) Relative Humidity :
- Maximum photosynthesis occurs at RH of 50-60 %.
- Generally during vegetative phase , RH is > 90 % from anthesis to maturity , RH lowers below 90 %.
- higher RH favours growth of insects and pathogens.
E) Wind velocity :
- Gentle wind of velocity between 0.75 to 2.25 cm/ second has a positive effect on photosynthesis and pollination.
- High velocity of wind causes lodging in long duration varieties.