Maharashtra Board Class 11 Agriculture Science and Technology Chapter 2 Weather and Climate PDF Download

Weather And Climate

2.1 Definition: Weather And Climate

2.1.1 Weather

Weather may be defined as follows.

Weather is the condition of the atmosphere at a particular place over a short period of time.

Weather refers to every day changes in the behaviour of atmosphere at the given place and a given time.

Do You Know?

Which are the different cropping seasons in Maharashtra? How they are identified?

What is the difference between weather and climate?

What is the role of meteorological department in farming?

What do you mean by meteorology, agrometrology and atmosphere?

Remember This

The success or failure of crops is intimately related to weather condition during the crop growth period. People often confuse weather with climate, but both are not the same. Between these two, climate is of prime importance. It is often rightly said that 50% of the variation in crop yields are due to climatic condition alone. Weather has significant influence on every phase of agricultural activity from preparatory tillage to harvesting. Climate is a factor which is beyond the control of farmer. Therefore, a sound knowledge of weather and climate with their elements is essential for successful agriculture.

Weather pertains to smaller area like village, city or even district and smaller duration of time i.e part of a day e.g. rainy day, hot day or cloudy weather, etc. It always differs from time to time.

2.1.2 Climate

Climate may be defined as follows.

Climate pertains to average weather condition over a period of time or season.

Climate is the weather conditions related to longer periods like month, season or year and is described by normal and average e.g. cold season, tropical, subtropical climate. It is more or less stable and differs from region to region.

Atmosphere

The earth has a thick layer of air called as the atmosphere.

It is colourless, tasteless and odourless mixture of gases that surrounds the earth. The atmosphere is present within a height of 32km from the earth surface.

Composition Of Air

According to NASA the gases in earth's atmosphere include.

Composition:

78% Nitrogen

21% Oxygen

0.03% Carbon dioxide

0.93% Argon

Teacher's Note

Weather changes every day but climate stays the same for many years. Like in Maharashtra, it rains in monsoon season every year.

Exam Trick

Remember: Weather = short time (today it is hot). Climate = long time (summer is always hot). Weather can change daily, climate cannot.

Points To Remember

Weather is for short time like one day or few hours.
Climate is for long time like seasons and years.
Weather changes daily but climate is stable.
Atmosphere is made of gases around the earth.
Nitrogen is 78% of the air we breathe.

2.2 Weather Elements And Their Effect On Crop Growth

2.2.1 Temperature

Temperature is the degree of hotness or coldness of a substance. Solar radiation is the main source of heat energy through which the atmosphere is indirectly heated up.

The rotation of earth cause the change in temperature during day and night. Temperature is measured by thermometer calibrated in the scale of Celsius (°C), Fahrenheit (°F) and Kelvin (°K).

Try This

Observe the thermometer and convert the reading from Celsius into Fahrenheit °F = \[\frac{9}{5}\]°C + 32

Fahrenheit into Celsius °C = \[\frac{5}{9}\](°F - 32)

Celsius into Kelvin °K = °C + 273

Effect Of Temperature

Temperature has great influence on the existence of plants. Each plant species has maximum and minimum limits of temperature for growth. Optimum temperature is essential for better growth and development of plants. Most of the crop plants make their best growth and development between 7°C to 32°C. Optimum temperature is necessary for seed germination, vegetative growth, flowering, fruiting, maturity and higher yields. Photosynthesis and respiration rate increases in high temperature. It also reduce sugar content, increase water requirements. Low temperature causes chilling or freezing injuries.

Teacher's Note

Temperature is very important for crops. Different crops need different temperatures to grow well, just like rice needs heat and wheat needs cool weather.

Exam Trick

Remember: Best crop growth = 7°C to 32°C. Too cold or too hot = bad for plants. Write this temperature range in your exam.

Points To Remember

Temperature is measured with a thermometer.
Most crops grow best between 7°C to 32°C.
High temperature increases photosynthesis rate.
Low temperature causes freezing injury to plants.
Temperature changes between day and night.

2.2.2 Rainfall

Rainfall is precipitation in the form of liquid drops larger than 0.5 mm in diameter falling on earth. Ordinary rain drop varies from 0.5 to 4 mm in diameter.

Effect Of Rainfall

Rainfall has beneficial as well as harmful effects on crop growth.

It is the main sources of water for plant growth. Water performs number of vital functions in crop growth. Quantity of rainfall is not only important but its even distribution increases crop yield. Rainfall pattern determines cropping system. It reduces salt, maintains pH and nutrient availability.

Heavy and excess rain results in flood and waterlogged condition in the field. Flood causes soil erosion and damage to the crops on river banks. Water logging affects soil aeration and root function. Heavy rain affect pollination and fertilization. Long dry spell affect growth and yield of the crop. Heavy and continuous rains during harvesting period result in prolonged harvesting time. There may be mouldy grain formation on earhead, which reduce quality of entire produce.

Teacher's Note

Rainfall is like the blood of farming in India. Without rain, crops cannot grow. Too much rain can also damage the crops by making the field waterlogged.

Exam Trick

Remember: Rain drops = 0.5 to 4 mm. Good rain = good crops. Heavy rain = soil erosion and floods. Write this in your exam.

Points To Remember

Rainfall is water that falls from clouds to earth.
Water is most important for crop growth.
Even distribution of rain increases crop yield.
Heavy rain causes floods and soil erosion.
Waterlogging affects root function of plants.

2.2.3 Sunlight (Solar Radiation)

Sun is the prime source of energy injected into the atmosphere. Solar radiation is received in the form of electromagnetic waves. It consist of stream or flow of particles. These particles are called quanta or photon.

Effect Of Sunlight

Growth of crop is favoured by sufficient sunlight and retarded by lack of sunlight. Quantity, duration and intensity of solar radiation influences plant development and plant processes. It is necessary for photosynthesis, the process in which green plant prepare their own food material. The life process of many plants is influenced by the length of day which is called photoperiodism. On the basis of photoperiod required for flowering plants are classified as short day and long day plants. Red and blue colour light stimulate plant growth, flowering, while green light has minimum effect. Insufficient light produces weak plants which are susceptible to diseases.

Teacher's Note

Sunlight is food for plants. Without sunlight, plants cannot make food through photosynthesis. This is why we grow plants in sunny places like fields and gardens.

Exam Trick

Remember: Red and blue light = good for plants. Green light = no use. Photosynthesis needs light. Short day and long day plants depend on sunlight hours.

Points To Remember

Sun is the main energy source for all plants.
Plants need light for photosynthesis to make food.
Red and blue light help plants grow well.
Photoperiodism = how many hours of light plants need.
Insufficient light makes weak plants that get diseases.

2.2.4 Humidity

Humidity refers to the water vapour content of the atmosphere. Liquid water is converted into water vapour by evaporation. The amount of water vapour in the atmosphere depends upon wind and temperature.

Humidity are of two types (a) Specific humidity (relative). It means weight of water vapour per unit weight of air (including water vapour). (b) Absolute humidity - It is actual quantity of water vapour by weight present in a given volume of air.

Do This

Distribute different agronomic crops as short day and long day crop on the basis of photoperiod. Also distribute crops which are grown as irrigated and rainfed.

Try This

Calculate absolute humidity (g/m³) when 2 cubic metres of air contains 10 g of water vapour.

Use formula - Absolute humidity (g/m³) = \[\frac{\text{Weight of water vapour}}{\text{Volume of air}}\]

Effect Of Humidity

Relative humidity directly influences water relations of plants and affects crop growth. High humidity reduce transpiration and evaporation losses of soil water. Low humidity increases the water requirements of the crop and affect the growth and yield of crop. Atmospheric humidity affects pollination, photosynthesis, flowering, fruiting, etc.

Leaf enlargement is more in humid condition. High humidity increases the attack of pest and diseases.

Teacher's Note

Humidity is the water in the air. High humidity in monsoon makes plants wet and can cause diseases. Low humidity in summer makes plants dry quickly.

Exam Trick

Remember: High humidity = high pest and diseases. Low humidity = more water needed by crops. Two types = relative and absolute humidity.

Points To Remember

Humidity is the amount of water vapour in air.
High humidity reduces transpiration loss.
Low humidity increases crop water needs.
High humidity increases pest and disease attack.
Relative humidity is shown as a percentage.

2.2.5 Wind

Wind is the horizontal flow of gases from high pressure area to a low pressure area. The natural movement of air, especially in the form of current air blowing from particular direction. Lee ward - from which it blows and wind ward - where it blows.

Effect Of Wind

Wind increases crop water requirements by increasing evaporation. It is useful for pollination in cross pollinated crops. It helps to increase supply of carbon dioxide for photosynthesis. Wind alters balance of hormones. Wind helps in winnowing operation. Tall crops during high wind velocity lodge which adversely affect quality as well as quantity of yield. It also causes shedding of flowers and fruits, damages shoot, increases rate of evaporation and transpiration, reduces soil moisture, causes soil erosion.

Teacher's Note

Wind can be good and bad for crops. Light wind helps flowers pollinate. Strong wind can break tall plants and blow away flowers and fruits like in a storm.

Exam Trick

Remember: Light wind = good for pollination and CO2 supply. Strong wind = lodging (plants fall down), flower shedding, soil erosion. Wind ward = where wind goes. Lee ward = where wind comes from.

Points To Remember

Wind is the flow of air from high to low pressure area.
Light wind helps in pollination of crops.
Strong wind causes lodging of tall crops.
Wind increases evaporation from soil.
Wind helps in winnowing grain after harvest.

2.2.6 Dew

Dew is water in the form of droplets that appears on thin object in the morning or evening due to condensation. The temperature at which condensation occurs is called the dew point. It is the form of direct condensation of water vapour to liquid drops. It occurs on grass cover, leaves, metallic surface, paper, window glasses, etc.

Effect Of Dew

It occurs in winter season during morning hours and useful for dry rabi crops like wheat, gram, etc. Foliar absorption of dew is an important factor in survival of natural vegetation in arid region. Dew reduces transpiration losses of water and minimizes crop water requirements. Dew formation increases humidity which increase incidence of pest and diseases.

Teacher's Note

Dew is the water drops you see on grass in early morning in winter. It helps dry crops like wheat get water without irrigation. But too much dew can cause diseases.

Exam Trick

Remember: Dew = water droplets in morning. Dew point = temperature where dew forms. Dew good for rabi crops like wheat and gram. High dew = more pests and diseases.

Points To Remember

Dew is water droplets that form on objects at night.
Dew point is the temperature where dew forms.
Dew reduces water loss from plants.
Dew is helpful for winter crops like wheat.
Too much dew increases pest and disease attack.

2.2.7 Fog

Fog is a visible aerosol consisting tiny water droplets or ice crystals suspended in the air at or near the earth surface.

Teacher's Note

Fog is like a cloud on the ground. You see it in winter mornings. It reduces sunlight reaching plants and can cause leaf diseases in vegetables.

Exam Trick

Remember: Fog = low-laying cloud. Forms when temperature falls below dew point. More than 75% humidity needed. Fog in winter season mostly. Harmful for vegetables.

Points To Remember

Fog is tiny water droplets suspended in air near ground.
Fog forms in early morning in winter season.
Fog needs more than 75% humidity to form.
Fog reduces sunlight and increases diseases.
Fog increases soil water availability.

Can You Imagine?

Why particular crop is grown in specific region and season?

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