(ii) Photosynthetic effect of Radiation: A portion of solar radiation upto 28% of energy is used in photosynthesis.
(iii) Photoperiodic effect: It plays an important role as regulator and controller of growth and development. Temperature Cardinal Temperature: For each species of plants, there are maximum and minimum limits of temperature as at which growth is negligible optimum temperature at which growth is maximum. Most of the crop plants grow at 15 °C to 30 °C. Influence on Growth Substances: At optimum temperature, the activity of the growth promoters are high and activity of the growth regulator is low with the result that growth rate is increased.
At high or low temperature, the balance of growth substances change and affect growth. Influence of Temperature on Development: Temperature has great influence on developmental rates like rate of germination, leaf initiation, tillering, flowering. Spikelet initiation and grain filling. All the development processes proceed at a faster rate at higher temperature. Low Temperature Stress: Cell division and cell elongation. Photosynthesis. Water transport. Vegetative growth.
Reproductive growth. Rainfall: Rainfall analysis helps in taking decisions on time of sowing. Scheduling of irrigation, time of harvesting etc.
Amount of Rainfall: Rainfall may also be in excess of the optimum and thereby cause reduced yields which may appear paradisiacal to semi arid climates. When the rainfall is concentrated in 4-5 months of the year, there may be periods when the rate of precipitation exceeds the intake rate of soil. Intensity of Rainfall: It influences erosion of soil.
Relative Humidity: Relative humidity has considerable influence on evapotranspiration and hence on the water requirement of crops. Photosynthesis: When relative humidity is low, transpiration increases causing water deficit in plant. Water deficit cause partial or full closure of stomata and increase mesophyll resistance blocking entry of CO2.
Pests: The incidence of insect pests and diseases is higher under high humidity conditions. Grain Yield: Very high or very low relative humidity do not conducive for high grain yield. Impact of changing environment on cropping pattern as indicators of environment.
Factors Responsible for Environment Change:
i. Human population ii. Urbanisation and industrialisation iii. Fossil fuel utilization — over exploitation iv. Deforestation v. Mismanagement in agriculture vi. Emission of green house gases Impact in India (i) Increasing temperature: a) Tree line shifting towards the higher altitude (Apple in Shimla).
b) Delaying of sowing of wheat crop. c) Rabi crop in north India production is under threatened (wheat, rapeseed, chick pea). (ii) Precipitation: a) All mathematical models projection is increase in precipitation in India. b) But the intensity will be more i.
e. less rainy days which cause floods and drought. c) Which cause production decline? (iii) CO2 level increase: a) Favourable for C3 plants upto some extend. b) But increase the C3 weed competition to C4 plants.
c) Increase the production and reduce the quality of the produce. Finally due to climate change the wheat production in north India will be severely affected and the people should change their food habit towards rice.