AGRICULTURE (808) - Academics

Unit II: Physical EnvironmentA. Climate and Weather, Elements of Weather, Rainfall, Temperature,Humidity, Wind, Sunshine.Climate Change, Global warmingMeteorologyMeteorology can be defined as the Science of atmosphere which deals with thephysics, chemistry and dynamics of atmosphere and also their direct and indirect effects upon the earthsurface, oceans and thereby Life in generalClimatology:- It is defined as a scientific study of climate. It discovers, describes, & interprets the climate onthe basis of cause’s processes that generate them.OrClimatology is the science which studies average condition of weather or the state behavior of theatmosphere over a place or region for a long period of time.Ecology:- In general ecology is a branch of biology that deals with the relation of living things to theirsurroundings.Weather:- Weather is the atmospheric condition of any place for a short period of time with respect to itsone or more elements such as temperature, pressure, wind, humidity, precipitation, sunshine, cloud cover etc.The periods of the year which are characterised by particular set of weather conditions are mainlycaused by the inclination of the earth’s axis and the revolution of the earth around the sun, are known asseasons.Climate:- The average weather conditions, prevalent from one season to another in the course of a year, overa large area is known as climate. The average of these weather conditions is calculated from the datacollected for several year (about 35 years) for a larger area. Rajasthan, for example, experiences hot and aridclimate, Kerala has tropical rainy climate, Greenland has cold desert climate and the climate of Central Asiais temperate continental. Climate of a region is considered more or less permanent.Sr NoDifference between weather and climateWeatherClimate1Instantaneous physical state of atmosphereat particular place.Normal physical state or generatedcondition of atmosphere or long termaverage condition of a place.2Weather changes refer to specific instant oftime( day or week)It is generalized over a longer span of timeand for a longer area.3It is expressed in terms of numerical valuesof meteorological elements.It is expressed in terms of time averagesand area averages of meteorologicalelements.4Weather is measured in observatory. So theobservatory must at a place for whichweather is to be described.This is derived information on regionalbasis. So scripts of observatories extendingover a region are necessary.5It provides meteorological information.It constitutes geographical information inrespect of weather.6Weather of two places having samenumerical value must be same.Climate of the two places having the sameaverages of weather can not be same,because their distribution over the years9

may be different.1.7Weather can be categorized as fair, unfair,excellent etc.Climate is classified as desert climate,marine climate, tropical climate etc.8Weather decides the success or failure of acrop in a particular season.Climate decides the type of crop suitablefor a region, while introducing new cropsclimate is considered.9Adverse weather results into crop failure orloss and warrants short term contingentplanning.Climate is considered in long termsagricultural planning.Weather forecast:- Means any advance information about the probable weather in future, which is obtainedby evaluating the present and past meteorological conditions of the atmosphere is called weather forecast.Agricultural weather forecast:- Forecasting of weather elements viz sunshine hours, occurrence of dew,relative humidity, rainfall, temperature, winds etc. Which are important in agriculture and for farmingoperations is known as agricultural forecast.In weather forecasting the advance information of weather elements like distribution of rain fall,warming for heavy rain fall, temperature change important special hazardous weather like if thunderstormhailstorm, show or frost, sky cover, winds, humidity, dew drought, evaporation rate etc is provided.Classification weather forecasting:- Weather forecasting on the basis of their validity periods or time scaleis classified as follows :1. Short range forecast (SRF):- It is based on synoptic situation prevailing at the time of forecasting and isvalid up to 3 days or 72 hrs and is issued twice a day. It broadcasted from local weather centre.2. Medium range forecast (MRF):- Forecasting of meteorological elements over different agro climaticzones for periods ranging from3-10 days is known as medium range forecast. It is broadcasted from WeatherForecasting Centre, Noida, UP.3. Long range forecast (LRF):- The forecast valid for more than 10 days i.e. a month or a season is knowsas long range forecast. It is broadcasted from Indian Metrology Department (IMD), Pune, Maharashtra.Facture affecting of Climate:Latitude or Distance from the EquatorThe places near the equator are warmer than the places which are far away from it. This is becausethe rays of the sun fall vertical on the equator and slanting in the temperate and polar regions. The verticalrays are concentrated over a small area than the slanting one.Again, the vertical rays pass through a shorter distance in the atmosphere before reaching theearth’s surface. Therefore, lower the latitude higher is the temperature and vice versa. Malaysia which isnear the equator is warmer than England which is far way from the equator.2. Altitude or the Height from the mean sea levelWe all know that mountains are cooler than the plains. Shimla situated on a higher altitude iscooler than Jalandhar, although both are almost on the same latitude. The temperature decreases with theheight of a place. For a vertical rise of 165 metres there is an average decrease in temperature at the rate of1 C. Thus the temperature decreases with increase in height.3. Continentally or the Distance from the SeaThe water is a bad conductor of heat i.e. it takes longer time to heat and longer time to cool. Dueto this moderating effect of the sea, places near the coast have low range of temperature and highhumidity. The places in the interior of the continent do not experience moderating effect of the sea. Theseplaces have extreme temperatures. The places far from the sea have higher range of diurnal (daily) andannual temperatures. Mumbai has relatively lower temperature and higher rainfall than Nagpur, althoughboth are almost situated on the same latitude.4. Nature of the Prevailing WindsThe on-shore winds bring the moisture from the sea and causerainfall on the area through which they pass. The off-shore winds coming from the land are dry10

and help in evaporation. In India, the on-shore summer monsoon winds bring rains while offshore winter monsoon winds are generally dry.5. Cloud CoverIn areas generally of cloudless sky as in deserts, temperature even under shade are very highbecause of the hot day time sunshine. At night this heat radiates back from the ground very rapidly. Itresults in a large diurnal range in temperature. On the other hand under cloudy sky and heavy rainfall atThiruvananthapuram the range of temperature is very small.6. Ocean CurrentsOcean waters move from one place to another partly as an attempt to equalize temperature anddensity of water. Ocean currents are large movements of water usually from a place of warm temperatureto one of cooler temperature or vice-versa. The warm ocean currents raise the temperature of the coast andsometimes bring rainfall, while the cold currents lower the temperature and create fog near the coast. PortBergen in Norway is free from ice even in winter due to warm North Atlantic Drift while Port Quebec inCanada remains frozen during winter months due to chilling effect of the Cold Labrador Current in spiteof the fact that Port Quebec is situated in much lower latitude than Port Bergen. The on-shore windspassing over a warm current carry warm air to the interior and raise the temperature of the inland areas.Similarly, the winds blowing over cold current carry cold air to the interior and create fog and mist.7. Direction of Mountain ChainsThe mountain chains act as natural barrier for the wind. The on-shore moisture laden winds areforced to rise after striking against the mountain; and give heavy rainfall on the windward side. These windsdescending on the leeward side cause very low rainfall. The great Himalayas check the moisture ladenmonsoon winds from crossing over to Tibet. This mountain chain also checks biting polar cold winds fromentering into India. This is the reason for which northern plains of India get rains while Tibet remains aperpetual rain shadow area with lesser amount of rainfall.8. Slope and the AspectThe concentration of heat being more on the gentler slope raises the temperature of air above them.Its lesser concentration along steeper slopes lowers the temperature. At the same time, mountain slopesfacing the sun are warmer than the slopes which are away from the sun’s rays. The southern slopes ofHimalaya are warmer than the northern slopes.9. The Nature of the Soil and Vegetation CoverThe nature of soil depends upon its texture, structure and composition. These, qualities vary fromsoil to soil. Stony or sandy soils are good conductor of heat while black clay soils absorb the heat of thesun’s rays quickly. The bare surface reradiates the heat easily. The deserts are hot in the day and cold in thenight. The forest areas have lower range of temperature throughout the year in contrast to non-forested areas.Weather componentsNearly 50 % of yield is attributed to the influence of climatic factors. The following are the atmosphericweather variables which influences the crop production.1. Precipitation:- Precipitation includes all water which falls from atmosphere such as rainfall, snow, hail,fog and dew.Rainfall one of the most important factor influences the vegetation of a place. Total precipitation in amount and distribution greatly affects the choice of a cultivated species in aplace. In heavy and evenly distributed rainfall areas, crops like rice in plains and tea, coffee and rubber inWestern Ghats are grown. Low and uneven distribution of rainfall is common in dryland farming where drought resistancecrops like pearl millet, sorghum and minor millets are grown. In desert areas grasses and shrubs are common where hot desert climate exists Though the rainfall has major influence on yield of crops, yields are not always directly proportionalto the amount of Precipitation as excess above optimum reduces the yields Distribution of rainfall is more important than total rainfall to have longer growing period especiallyin drylands2. Temperature:- Temperature is a measure of intensity of heat energy. The range of temperature formaximum growth of most of the agricultural plants is between 15 and 40ºC.11

The temperature of a place is largely determined by its distance from the equator (latitude)and altitude. It influences distribution of crop plants and vegetation. Germination, growth and development of crops are highly influenced by temperature. Affects leaf production, expansion and flowering. Physical and chemical processes within the plants are governed by air temperature. Diffusion rates of gases and liquids changes with temperature. Solubility of different substances in plant is dependent on temperature. The minimum, maximum (above which crop growth ceases) and optimum temperature ofindividual’s plant is called as cardinal temperature.CropsMinimumOptimumMaximumtemperature ºCtemperatureºCtemperature -1428-3036-38Sorghum8-1030-3236-38Average for rage for Rabi0-525-3031-353. Atmospheric Humidity (Relative Humidity - RH):- Water is present in the atmosphere in the formof invisible water vapour, normally known as humidity. Relative humidity is ratio between theamounts of moisture present in the air to the saturation capacity of the air at a particulartemperature.If relative humidity is 100% it means that the entire space is filled with water and thereis no soil evaporation and plant transpiration. Relative humidity influences the water requirement of crops Relative humidity of 40-60% is suitable for most of the crop plants. Very few crops can perform well when relative humidity is 80% and above. When relative humidity is high there is chance for the outbreak of pest and disease.4. Solar radiation (without which life will not exist):- From germination to harvest and even postharvest crops are affected by solar radiation. Biomass production by photosynthetic processes requires light. All physical process taking place in the soil, plant and environment are dependent on light Solar radiation controls distribution of temperature and there by distribution of crops in aregion. Visible radiation is very important in photosynthetic mechanism of plants.Photosynthetically Active Radiation (PAR - 0.4 – 0.7µ) is essential for production ofcarbohydrates and ultimately biomass. 0.4 to 0.5 µ - Blue – violet – Active12

0.5 to 0.6 µ - Orange – red - Active 0.5 to 0.6 µ - Green –yellow – low active Photoperiodism is a response of plant for flower inatation to day length. Basis of photoperidism plantclassified in 4 gropus.1. Short Day Plnt:- If any plant require less than 9 hours day lenght for flower ination is calledShort Day Plant. Eg. Rice, lima bean, cluster bean and cotton.2. Long day Plants:-If any plant require more than 13 hours day length for flower ination is calledLong Day Plant. Eg.Barley, oat, carrot, onion, garlic and cabbage3. Day neutral Plant:- If any plant flower inatation is no or less influence on day length. Eg.Tomato, maizerinjal, cucurbits, chilli etc. Phototropism –– Response of plants to light direction. Eg. Sunflower Photosensitive – Season bound varieties depends on quantity of light received5.Wind velocity: The basic function of wind is to carry moisture (precipitation) and heat. The moving wind not only supplies moisture and heat, also supplies fresh CO 2 for thephotosynthesis. Wind movement for 4 – 6 km/hour is suitable for more crops. When wind speed is enormous then there is mechanical damage of the crops (i.e.) it removes leavesand twigs and damages crops like banana, sugarcane. Wind dispersal of pollen and seeds is natural and necessary for certain crops. Causes soil erosion. Helps in cleaning produce to farmers. Increases evaporation. Spread of pest and diseases.5. Atmospheric gases on plant growth Atmosphere Composition:- CO2 – 0.03%, O2 - 20.95%, N2 - 78.09%, Argon - 0.93%, Others - 0.02%.CO2 is important for Photosynthesis, CO2 taken by the plants by diffusion process from leavesthrough stomataCO2 is returned to atmosphere during decomposition of organic materials, all farm wastes and byrespirationO2 is important for respiration of both plants and animals while it is released by plants duringPhotosynthesisNitrogen is one of the important major plant nutrient, Atmospheric N is fixed in the soil by lightning,rainfall and N fixing microbes in pulses crops and available to plantsCertain gases like SO2, CO, CH4, HF released to atmosphere are toxic to plantsClimate Change, Global warmingClimate change, also called global warming, refers to the rise in average surface temperatures on Earth.Temperature records going back to the late 19th Century show that the average temperature of theEarth's surface has increased by about 0.8C (1.4F) in the last 100 years. About 0.6C (1.0F) of this warmingoccurred in the last three decades.Satellite data shows an average increase in global sea levels of some 3mm per year in recent decades.A large proportion of the change in sea level is accounted for by the thermal expansion of seawater. Asseawater warms up, the molecules become less densely packed, causing an increase in the volume of theocean.But the melting of mountain glaciers and the retreat of polar ice sheets are also importantcontributors. Most glaciers in temperate regions of the world and along the Antarctic Peninsula are in retreat.Since 1979, satellite records show a dramatic decline in Arctic sea-ice extent, at an annual rate of 4% perdecade. In 2012, the ice extent reached a record minimum that was 50% lower than the 1979-2000 average.13

The Greenland Ice Sheet has experienced record melting in recent years; if the entire 2.8 millioncubic km sheet were to melt, it would raise sea levels by 6m.Satellite data shows the West Antarctic Ice Sheet is also losing mass, and a recent study indicatedthat East Antarctica, which had displayed no clear warming or cooling trend, may also have started to losemass in the last few years. But scientists are not expecting dramatic changes. In some places, mass mayactually increase as warming temperatures drive the production of more snows.The effects of a changing climate can also be seen in vegetation and land animals. These includeearlier flowering and fruiting times for plants and changes in the territories (or ranges) occupied by animals.Causes of Global WarmingGreenhouse GasesSome gases in the Earth's atmosphere act a bit like the glass in a greenhouse, trapping the sun's heatand stopping it from leaking back into space.Many of these gases occur naturally, but human activity is increasing the concentrations of some of them inthe atmosphere, in particular: carbon dioxide (CO2)methanenitrous oxidefluorinated gasesCO2 is the greenhouse gas most commonly produced by human activities and it is responsible for64% of man-made global warming. Its concentration in the atmosphere is currently 40% higherthan it was when industrialisation began.Other greenhouse gases are emitted in smaller quantities, but they trap heat far more effectivelythan CO2, and in some cases are thousands of times stronger. Methane is responsible for 17% ofman-made global warming, nitrous oxide for 6%.Causes for rising emissionBurning coal, oil and gas produces carbon dioxide and nitrous oxide.Cutting down forests (deforestation). Trees help to regulate the climate by absorbing CO2 from theatmosphere. So when they are cut down, that beneficial effect is lost and the carbon stored in thetrees is released into the atmosphere,adding to the greenhouse effect.Increasing livestock farming. Cows and sheep produce large amounts of methane when they digestth

1. Agronomy word drive from two Greek word "Agros" means field and "Nomos" means to manage. Agronomy (Greek) Definition:-It is defined as an agricultural science deals with principles and practices of crop production and field management. or Agronomy is branch of agricultural science, which deals with principles, & practices of soil,