External or Environmental Factors- Anthropic or Management or Man or Skillful Mgt & climate
Anthropic or Management /Man or skillful management by the man:
Finally, man must so manage the soil-water-plant complex to produce efficiently food & fodder and for that purpose a number of mechanical devices & useful cultivation practices have been evolved such as ploughs for ploughing, harrows for seeded preparation, hoes for hoeing, seed cum fertilizer driller for sowing the seeds & application of fertilizers. Man has to perform the operations at proper time such as land preparation sowing, thinning & gap filling and also the plant protection measures, optimum plant population, recommended fertilizer application at right time & depth, proper water mgt Practices. The soil, water, plant& management are the four factors, which govern successful crop production.
Climate: Another factor that influences the growth, development, & production of crop is the climate which is out of control by the man but mgt. practices of the crops can be altered to harvest maximum yield. Climate is the most dominating factor influencing the suitability of a crop to a particular region. The yield potential of a crop mainly depends on climate. More than 50% of variation in yield of crops is solar radiation, temperature & rainfall Relative humidity & wind velocity also influence crop growth to some extent. Atmospheric factors which affect the crop plants are called climatic factors which include.
1. Precipitation,
2. Temperature,
3. Atmospheric humidity,
4. Solar radiation,
5. Wind velocity and atmospheric gases.
1. Precipitation: – It results from evaporation of water from sea water and land surfaces. The process involved in the transfer of moisture from the sea to the land & back to the sea again what is known as the hydrologic cycle. Continuous circulation of water between hydrosphere, atmosphere & lithosphere called as hydrologic cycle. Precipitation includes rainfall, snow or hail, Fog drip & dew also contribute to moisture. Fog consists of small water droplets while dew is the condensation of the water vapour present in the air. Precipitation influences the vegetation of a place. Most of crops receive their water supply from rainwater which is the source of soil moisture so essential for the life of a plant. The yearly precipitation, both in total amount & seasonal distribution greatly affects the choice of cultivated crops of a place.
2. Temperature: It is considered as a measure of intensity of heat energy. The range of maximum growth for most argil, plans is between 15 & 400C, every plant community has its own minimum, optimum & maximum temperature known as their cardinal points. Temperature is determined by the distance from the equator (latitude) and the altitude; Apart from the reduction in yield many injuries such as cold injury which included chilling injury, freezing injury, suffocation & heaving and heat injury.
Maize & sorghum (8-100C, 300C, 40ºC) Rice (10-110C, 35ºC) Wheat (50C, 25ºC, 30º-320C)
3. Atmospheric humidity: Water which is present in the atmosphere in the form of invisible water vapor, termed as humidity of the air, ET of crop plants increases with the temperature but decreases with high relative humidity affecting the quantity of irrigation water, Moist air favors the growth of many fungi & bacteria which affect seriously the crop.
4. Solar radiation: Solar energy provides two essential needs of plants:
a) Light required for photosynthesis & for many other functions of the plant including seed germination, leaf expansion, growth of stem & shoot, and flowering, fruiting & even dormancy.
b) Thermal conditions required for the normal physiological functions of the plant. Light helps in synthesis of chlorophyll pigment. Light affects the plants in four ways: intensity, quality (wave length), duration (Photoperiod) and direction.
5. Wind velocity: It affects growth mechanically (damage to crop) and physiologically (evaporation & transpiration), Hot dry winds may adversely affect photosynthesis & hence productivity, by causing closure of the stomata even when soil moisture is adequate. Moderate winds have a beneficial effect on photosynthesis by continuously replacing the CO2 absorbed by the leaf surfaces.