Climate is the most important dominating factor influencing the suitability of a crop to a particular region. The yield potential of the crop mainly depends on climate. More than 50 per cent of variation of crops is determined by climate. The most important climatic factors that influence growth, development and yield of crops are solar radiation, temperature and rainfall.
Effect of Temperature on Plant Growth
Temperature and crop production
Important for growth and development
Optimum temperature is required for maximum dry matter accumulation.
High night temperature – growth of shoot
Cardinal temperature points
All plants have maximum, optimum and minimum temperature limits. The limits are cardinal temperature points. Optimum temperature range is very important.
Wheat
3 – 4°C
minimum
25°
optimum
30° - 32°C
maximum
Rice
10-12°C
minimum
30-32°C
optimum
36-38°C
maximum
(1) Low temperature injury
(2) High temperature injury
1) Low temperature:
Low temperature affects several aspects of crop growth viz., survival, cell division, photosynthesis, water transport, growth and finally yield.
Chilling injury
If the plants grown in hot temperature are exposed to low temperature, they will be killed (or) severely injured. When the night temperature is below 15°C field crops may show yellowing symptoms (eg) Tropical annuals.
Freezing injury
When the plants are exposed to how temperature, water freezes into ice crystals in the intercellular spaces.
(eg) Cell dehydration
Temperate crops (potato, tea etc.,)
Suffocation
Formation of thick cover of ice/snow on the soil surface presents the entry of oxygen and crop suffers. This presents the respiration and lead to accumulation of harmful substances.
Heaving
Lifting of plants along with soil from its actual position by ice, crystals. This is a mechanical lifting.
Frost damage:
Low temperature near the canopy due to earth’s re-radiation. If the cell size is large the probability of frost damage is high.
(1) Advective frosts
Advective frosts are due to incursion of large masses of cold air over a region from the colder areas.
(2) Radiation frost:
Occur on clear calm nights when heat is freely radiated from all exposed objects.
(i) Hoar frost (or) white frost:
This is caused due to sublimation of ice crystals on objects like tree branches.
(ii) Black frost:
The vegetation is frozen because of reduction of air temperature.
Plant management against frost damage:
Frost free growing season
Adjusting the sowing time
Selection of resistant varieties
Sprinkler irrigation
HIGH TEMPERATURE INJURIES High temperature adversely affects mineral nutrition, shoot growth and pollen development resulting in low yield.
The critical temperature above which plants gets killed is called thermal ‘death point’.
The temperature above 50°C may kill many annual crops. –
The limit varies with plants; shade loving plants are killed at lower temperature.
Mineral Nutrition
High temperature stress causes reduction in absorption and subsequent assimilation of nutrients.
Absorption of calcium is reduced at temperature of 28º C in Maize.
Nutrient uptake is affected by both soil and air temperature in rice.
Nitrate reductase activity decrease under high temperature.
Shoot growth
High temperature, even for short period, affects crop growth especially in temperate crops like wheat.
High air temperature reduces the growth of shoots and in turn reduces root growth.
High soil temperature is more crucial as damage to the roots is severe resulting in substantial reduction in shoot growth.
High temperature at 38º C in rice reduced plant height, root elongation and smaller roots.
Pollen development
High temperature during booting stage results in pollen abortion.
In wheat, temperature higher than 27º C caused under-development of anthers and loss of viability of pollen.
A temperature of 30º C for two days at reduction division stage decreased grain yield by drastic reduction in grain set.
Scorching:
High temperature lead to dehydration and leaves are scorched.
Physiological activities:
High temperature disturbs the photosynthesis and respiration.
Injury due to scorching sun:
High temperature causes injury on the exposed area of the plant (eg) Barcks it is know as ‘Sun sclad’
Burning off:
The symptoms are noticed on young seedlings due to high soil temperature. The seedlings are killed.
Stem gridle:
High soil temperature causes stem scorches at the ground level (eg) cotton.
