পৃষ্ঠাসমূহ

Factors Affecting Growth of Crops :

Factors Affecting Growth of Crops :

Crop growth factors :

The factors that affect the vegetative and reproductive growth of crop are called crop growth factors. Crop growth factors may be shown in following diagram.

Factors




Biological

Non biological















Fig. Factors affecting crop growth.

A. Non-biological factors :

1. Climate factors :

(e) Light :

Plant produces carbohydrate using CO2 and water with the help of light and chlorophyll. This process is called photosynthesis. It is expressed by the following equation.

6CO2+ 12 H2O light & chlorophyll C6H12O6 + 6O2 + 6H20

Only Visible light of the radiant energy spectrum having 400 to 700 nm wavelength is used by the plant for photosynthesis. This is known as Photosyntheically Active Radiation (PAR). Leaf holds some part of the sight falling on it which is called intercepted radiation and the rest is either reflected or passed downward through the leaf. The solar radiation falling on the green part of the plant affects the plant growth positively i.e. The more the fractional intercepted radiation in the green plants, the more the growth of the plant. Thus plant growth can be expressed by the following equation.

W = Es Esc

Where, W = Dry matter

Es = Conversion efficiency or light use efficiency

Si = Intercepted radiation

Esi = Cumulative total of intercepted radiation.

Light intensity :

Very low high intensity reduces the rate of photosynthesis and may even results in the closing of the stomata. This result in reduced vegetative growth of the plants. At very high intensity plants become thick and dwarf. It increases the rate of respiration and thus disturbs the photosynthesis-respiration balance. It causes rapid loss of water resulting in the closure of stomata.

In addition to photo synthesis, light also play role in chlorophyll formation. In the absence of light etiolin is produced in the plant. As a result, plants become yellowish which is called etiolating.

(ii) Temperature :

Temperature affects the plant growth directly and indirectly almost all physiological processes of plant such as germinations photosynthesis, respiration, absorption, osmosis, etc. are influenced by air and soil temperature. Basically, the quantitative difference between photosynthates produced in plant by photosynthesis and the photosynthates exhausted by respiration is the plant growth which is, in general, measured by the dry matter accumulation in the plant.


During the day adequate sunshine and high temperature increase the rate of photosynthesis and respiration whereas low temperature during night reduces the rate of the two processes. Consequently such environment of sunlight and temperature is conducive to plant growth. But assimilation process in plants take place within a certain temperature range. Plant growth occurs within the limit of maximum and minimum temperatures. Each plant community has its own minimum, optimum and maximum temperature known as their cardinal temperature. Cardinal temperature varies in different plant species (Table-1).

Table-1: Cardinal temperature of certain crops :

Crops

Min. (oC)

Opt. (oC)

Max. (oC)

Rice

5

30

40

Wheat

4

25

30-32

Maize

8-10

32

40-44

Tobacco

B-14

28

35

(iii) Precipitation :

Water is essential for plant growth, development and other physiological processes of the plant. It is a principal element of protoplasm. Through the process of osmossis the hydrostatic turgor pressure of the cell increases which results in the plant growth. Thus growth can be expressed as

Where, dt = an interval of time

dv = the change in the cell volume over this time interval

P = turgor pressure of the cell

Y = the thurgor pressure that must be exceeded before the cell wall with expand

M = cell wall extensibility.


With the rise of water potential in plant, leaf expansion rate increase. Due to the lack of water leaf is willed and the growth is arrested. Again, at excessive. Soil moisture content abnormal growth occurs or even the plant may die. Owing to continuous increase of water if the cell is saturated, differentiation is hampered. Experimental result shows that plant growth is optimum at moisture content slightly below the joe condition of the soil Fig.1










Text Box: Growth rate





Fig. 1. Effect of moisture on plant growth

At optimum soil moisture level transpiration increase plant growth is positively related to transpiration. Plant growth can be expressed as follows-

W = Ew E Et

Where,

W = Dry matter

Ew = Water use efficiency

E Et = Cumulative total evapotranspiration.

(iii) Air :

Oxygen and carbon dioxide are the most important components of the air relating to plant growth. Carbon of the CO2 is synthesized into carbohydrate through photosynthesis, and again this carbohydrate is oxidized and changed into chemical energy (ATP) through respiration. If oxidation is occurred in presence of air (O2), then 38 ATP is produced. But in anerobic respiration only 2 ATP is produced. This kinetic energy (ATP) helps to perform all the vital activities of plant.

Again, wind velocity helps indirectly in the growth of plant. Wind velocity enhances the rate of transpiration by lessening the density of air around the guard cell. As a result, plants absorb more water and minerals from the soil which accelerates plant growth. High wind tear the leaf and the plants are in danger of being uprooted and blown away. Lodging of crops (wheat, Rice, Maize, Sugarcane) are caused by violent winds.

(iv) Humidity :

Oxygen and carbon directly affects plant growth by influencing the rate of transpiration. In addition, it also influences the physiological processes of the plant by controlling temperature. At very low humidity the pollen grain dries up. Again, at very high humidity the pollen grains are attacked by fungi. As a consequence at both the conditions fertilization is impaired.

2. Edaphic Factors :

Soil provides physical support to plant as well as supplies necessary water and nutrient elements for plant growth and development. Plant growth basically depends on physical, chemical and biological properties of soil. They are discussed below:

a. Soil physical factors :

The main soil properties influencing crop growth are soil texture, soil structure matter, etc. Water and nutrient holding capacity of soil, soil aeration, drainage conditions, soil compactness etc. are influenced by soil texture. A certain crop prefers a specific soil texture. For example, through clay soil is suitable for rice growth, it does not favour the growth of potato tuber. Potato grows well in sandy or sandy loam soil.

Soil structure directly influence crop growth by influencing soil moisture, aeration and root growth. For example, grannular structured soil contains more macro pore and porosity of such soil is high. such soil is ideal for seedling establishment as root penetration and drainage of water takes place rapidly.

Soil temperature directly influences crop growth. The prevailing temperature of soil besides affecting the physical and chemical processes going on in the soil also influences to a very great extent the rate of absorption of water and solutes, the germination of seeds and the rate of growth of the underground portions of the plant body. The maximum absorption of water by the roots take place generally between 20 and 300C. Lowering of temperature below 200C causes an appreciable reduction in the rate of absorption of water.

b) Soil chemical factors :

Most important chemical factors influencing crop growth are plant nutrient elements and soil PH. Crop growth is influenced by the supplied plant nutrient. Again, the nutrient status of soil greatly influenced by the mineral content of the soil, derived from the weathering of the rocks and minerals. The total amounts of elements contained in soils depend partly on the nature of the rock from which they are formed and partly on their age and the extend to which solable products have been leached away. Nutrient availability of macro-nutrients and Mo increases with the increase of soil PH while microelements show a inverse relationship. Some plants prefer high acidity such as tea, fungi etc. But most plants grow well in slightly acidic to neutral soil. However, some plants grow well in alkaline soil e.g. sugar beet, lettace.

c) Soil biological factors :

In relation to plant growth soil biological factors are classified into two groups : beneficial and harmful. Fungi, bacteria, virus, nematode and so on affect plant growth directly. Some microorganisms play important role in maintaining soil fertility.

Rhizobium bacteria fix atmospheric nitrogen in the roots of legumes through symbiosis. But many microorganisms such as fungi, bacteria, nematodes and virus causes damage to the crop at different grows stages.

3. Habitating factors :

i) Attitude and topography :

With the change of attitude plant adaptation and ecology are changed which influence the distribution of plants in various ways. With the rise of attitude availability of solar radiation is altered including atmospheric humidity, temperature.

Land topography influences cropping patter. Again the fertility status of same AEZ may differ due to pography.

ii) Latitude :

With the change of latitude air temperature, pressure, rainfall, light and humidity are changed. Thus affect plant growth.


iii) Slope and direction :

Slope and directions influence the local climate. If the slope is high i.e. steep, water does not stand there. As a result, water lading capacity is limited there which affect plant growth.

Factors affecting development of crops :

1. Temperature :

For completing each development process in plant there is a certain level or limit of temperature in which the process of development continues. Like growth process development processes also have cardinal temperature, they are:

i. Base or threshold temperature :

At this temperature developmental process begins. It is expressed by Tb.

ii) Optimum temperature :

Development rate is highest at this temperature. It is expressed by to.

iii) Ceiling temperature :

At this temperature development rate is minimum and beyond this temperature the process of development is cased. It is expressed by tee.

Thermal time / Duration :

A certain temperature is required to complete the developmental process of temperature sensitive plant. Above base temperature when the total neat energy obtained from every day’s solar radiation equals to that certain temperature, the development process is ended. This means that with time cumulative heat energy is increased gradually and the developmental processes come to on end. At last it is observed that when the total heat is reached that certain limit the process of development is complete.

The half of the difference between ceiling temperature (Tce) and base temperature (Tb) is known as average temperature (Tce-Tb) = T. At the time of developmental process if every base temperature is cumulated a certain heat energy is obtained. This is called thermal duration or time.

q =

Where,

q = thermal time / duration

n = number of days during development

T = average temperature

Tb = base temperature

2) Light :

i) Photoperiod or day length :

Development processes of most plant species are influenced by day length. Flowering is one of the developmental processes of the plant which is affected by day length. Plant is divided into three classes on the basis of sensitivity of flowering to photo period, they are-

a. Photo insensitive or day neutral plant :

The plants where flowering is not dependent upon day length are called photoinsentive or day neutral plants e.g. groundnut, tomato, etc.

b. Short day plant :

Plants which flower when the day length is less than the critical length e.g. Tobacoo, Mustard etc.

c. Long day plant :

Plants which flower when the day length is longer than critical lengths e.g. Gram, wheat etc.

Note : The response of plants to the relative lengths, and alternations of light and dark periods with regard to the initiation of flowering is called photopenriodism.

3. Assimulate supply

4. Strees.

“Every living organism is a product of its biological heredity and its environment”. Explain


Every living organism (e.g. plant species) has a specific genetic make up. Complete expression of the potentiality of the genetic make up takes place under suitable environmental condition. If only of the environmental factors limit the growth and development of the plant, than, if fails to express it actual potentiality. For example, yield potentiality of BRRIdhan 29 (6.5 t ha-1), may not be achieved, if the would cultivate under stress condition. Thus environment can modify the genetical potentiality of crops. Again, cultivation of different cultivar (e.g. BR 3 and BRRIdhan 29) under same environment may give different yield due to difference in their genetical make up.