Introductory Agrometeorology/Atmospheric Temperature

Objectives of the chapter

• To understand:
  • diurnal and seasonal variation in temperature
  • measurement of ambient temperature
  • significance of atmospheric temperature in crop production

Diurnal and seasonal variation of air temperature

1. The minimum air temperature occurs at about sunrise after which there is a constant rise till it reaches to maximum.
2. The maximum air temperature is recorded between 1300 hrs and 1400 hrs although the

maximum solar radiation is reaches at the noon.

1. A steady fall in temperature till sunrise is noticed after is attains maximum. Thus the daily March displays one maximum and one minimum. The difference between the two is called the diurnal range of air temperature.
2. The diurnal range of air temperature is more on clear days while cloudy weather sharply reduces daily amplitudes.
3. The diurnal range of temperature is also influenced by soils and their coverage in addition to seasons.
4. Addition of daily maximum and minimum temperature divided by two is daily mean / average temperature.
5. In northern hemisphere winter minimum occurs in January and summer maximum in July.

Ambient temperature

the temperature of surrounding medium of given location at certain time is ambient temperature.

Measurement of Temperature

1. Mercury or alcohol in glass thermometer
2. Maximum-Minimum thermometer
3. Bimetallic Thermograph
4. Thermocouples
5. Thermistors

Signifiacnce

Low temperature

1. Low temperature damages the tender leaves and flowers.
2. Rapidly growing and flowering plants are severely affected.
3. Low temperature and wet soil increases the amount of toxic substances in the plant cells. The accumulation of toxic substances increases with the increasing wetness.
4. Extremely low temperature with snowfall(freezing and thawing) causes plants to get uprooted themselves.
5. Low night temperature increases the sugar content in plants. At optimum temperature (25 degree Celsius), sugar translocation in maximum.

High temperature

1. High temperature with high humidity is the cause of various plant diseases.
2. High night temperature increases the growth of leaves but decreases the growth of fruits, cambium, stolons, etc, causing imbalance in growth rates of various plant parts.
3. Temperature of 50-60 degree celsius is called thermal death point. At this range of temperature, plants die due to excessive heat.
4. High temperature results in desiccation, inhibits seedling growth and causes premature drop of fruits due to lack of starch.