1. Plant density and crop productivity
Plant distribution
Environmental factors affecting growth and yield
Strategies for maximizing solar energy utilization, leaf
area, interception of solar radiation and crop growth
Photosynthesis
Factors essential for photosynthesis
Physiological limitations to crop growth
Solar radiation concept and agro-techniques for
harvesting solar radiation
2. Plant density and crop productivity
Plant density is the number of plants per unit area in a
cropped field. It indicates the size of the area available
for individual plant.
Establishment of optimum plant population is essential
to get maximum yield.
3. FACTORS AFFECTING PLANT DENSITY
The factors affecting plant density are grouped
into two as
(a) Genetic
(b)Environment factors.
4. A. Genetic Factors (plant or internal factors)
(i) Size of plant - The volume occupied by the
plant at the time of flowering decides the spacing
of the crop.
• Plants of red gram, cotton, sugarcane etc.,
occupy larger volume of space in the field
compared to rice, wheat, etc. Even the
varieties of the same crop differ in size of
plant.
5. (ii) Elasticity of the plant - Variation in size or plant between the
minimum size of the plant that can produce some economic yield to
the maximum size of the plant that can reach under unlimited space
and resources is the elasticity of the plant.
For example, in indeterminate red gram varieties the optimum plant
density ranges from 55 to 133 thousand plants/ha. The elasticity of
plants is due to branching or tillering. For determinate plants like
maize, sorghum etc., the elasticity is less and hence the optimum plant
density range is small. The removal of auxiliary buds is done to get
uniform and early maturity in castor.
6. (iii) Foraging area or soil cover –
The crop should cover the soil as early as
possible so as to intercept maximum sunlight.
More interception of solar radiation leads to
more dry matter production. Closely spaced
plants intercept more radiation than widely
spaced plants. Area of root spread also decides
the density.
7. (iv) Dry matter partitioning –
Dry matter production is related to the amount
of solar radiation intercepted by the canopy,
which depends on the plant density. As the
plant density increases, the canopy expands
more rapidly, more radiation is intercepted and
more dry matter is produced.
8. B. Environmental Factors (management factors)
The primary management factor affecting the
plant density of any crop varieties is the
method of stand establishment/sowings like
transplanting or broadcasting. For
transplanting/direct drilling, the genetic factors
are the deciding factors on the number of
plants per unit area. For broadcasting, the
factors are:
9. (i) Time of sowing –
The crop is subjected to different weather conditions when sown
at different periods. Among the weather factors, the most
important factors that influence optimum plant density are day
length and temperature. Photosensitive varieties respond to day
length resulting in change in size of the plant. As low
temperature retards the growth, higher density is established for
quicker ground cover.
(ii) Rainfall/irrigation –
Plant density has to be less under rainfed than irrigated
conditions. Under higher plant densities, more water is lost
through transpiration. Under adequate irrigation or under evenly
distributed rainfall conditions, higher plant density is
recommended.
10. (iii) Fertilizer application - Higher plant density is
necessary to fully utilize higher level of nutrients in the
soil to realize higher yield. Nutrient uptake increases
with increase in plant density. Higher density under
low fertility conditions leads to development of
nutrient deficiency symptoms. For example, rice does
not respond to plant density without nitrogen
application.
(iv) Seed rate - Quantity of seed sown/unit area,
viability and establishment rate decides the plant
density.
11. Optimum plant density is necessary to obtain maximum
yield.
• Optimum plant density depends on size of the plant
• Elasticity
• Foraging area
• Nature of the plant,
• Capacity to reach optimum leaf area at an early date and
• Seed rate used.
12. CROP GEOMETRY
Crop geometry is the pattern of distribution of plant over
the ground or it refers to the shape of the space available
for individual plants. It influences crop yield through its
influence on light interception, rooting pattern and
moisture extraction pattern. Crop geometry is altered by
changing inter and intra-row spacing (Planting pattern).
• Plants which requires no restriction in all directions
are given square geometry
• Usually perennial vegetation like trees/shrubs are
under this arrangement
13. (i) Square planting - Square arrangements of plants will be more
efficient in the utilization of light, water and nutrients available to
the individual plants than in a rectangular arrangement.
(ii) Rectangular planting - Sowing the crop with seed drill,
wider inter-row and closer intra-row and closer intra-row
spacing leads to rectangularity. Rectangular arrangement
facilitates easy intercultivation. Rectangular planting mainly
suits annual crops, crops with closer spacing etc., the wider
section (row) is given for irrigation, intercultural operation etc.
• It is an arrangement to restrict the endless growth habit in order to
switch over from vegetation to the productive phase.
• This method accommodate high density planting
• It can facilitate intercropping also.
14. • (iii) Triangular planting - It is a method to accommodate
plant density under perennial/tree crops.
• (iv) Miscellaneous planting - In rice and ragi transplanting is
done either in rows or at random. Skipping of every alternate
row is known as skip row planting. When one row is skipped
the density is adjusted by decreasing inter-row spacing. When
theinter row spacing is reduced between two rows and
spacing between two such pair are increased then it is known
as paired row planting. It is generally done to introduce an
inter crop.
15. Yield of individual plant and community
The full yield potential of individual
plant is achieved when sown at
wider spacing.
When sown densely, competition
among plants is more for growth
factors resulting in reduction in the
size and yield of the plant.
Yield/plant decreases gradually as
plant population/area increases (Fig
1 below). However, yield/area is
increased due to efficient utilization
of growth factors. Highest yield/area
can, therefore, be obtained when
the individual plants are subjected
to severe competition.
16. • Decrease in the yield of individual plants at higher plant density is due to
reduction in the number of ears in indeterminate plants.
• In determinate plants, wherein the terminal bud ends in a flower or
inflorescence, the reduction in yield is mainly due to the reduced size of ears
or panicles.
• Highly branching or tillering plants behave as indeterminate plant and
yield reduction is due to reduction in the number of seeds.
• Red gram produces about 20 pods/plant at 3.33 lakh/ha while it produces
more than 100 pods/plant at 50000 plants/ha. Conversely, non-tillering or
non branching plants produce less yield due to reduction in size of ears as in
the case of maize and sorghum.
Plant population and yield
17. Plant distribution
• The organisms are influenced by their environment in a number of ways.
These environmental factors govern the survival and growth of individuals at all phases
of their life cycle.
• The distribution or physical location of individuals within a population at a particular
time is called dispersion.
• In other words, dispersion is the internal distribution pattern of individuals within a
population. The distribution of individuals in a population may follow three broad
patterns
Random Uniform Clumped
18. Random distribution
• Random distribution– in this case, the individuals in a
population are scattered over an area without regularly or any degree
of affinity for each other. The probability of locating an individual
at a point in the populated area is equal for all the point. Random
distribution is relatively rare in nature and is expected to occur only
when the environment is uniform and the resources are evenly spread.
There must also not be any interactions among individuals to repel
each other or social attractions causing tendency to aggregate. When
many small environmental factors are acting together on population,
random distribution is expected in nature. However, when a few
major factors are dominating, random distribution is not expected.
19. Uniform distribution
• Uniform distribution – In this case, the
individuals are evenly spaced and tend to be as far
apart from each other as possible within a
particular density. The distribution of individuals is
more regular than random. It may be found in
places where there is severe competition among
individuals or where positive antagonism is
predominant leading to even spacing.
20. Clumped distribution
Clumped distribution – Here the individuals of a population are found scattered in
groups here and there. This is perhaps the most common pattern of distribution and
may result from nonuniformity of the habitat or attraction among individuals. This is
also called irregular or nonrandom distribution. There may be variations in the
intensity of clumped distribution and it may be present only at certain times of the
individual’s life cycle. The seeds from annual or perennial plants will normally drop
nearer to the parent and hence clumps of genetically related individuals may
characterize the distribution. However, the distribution of groups may tend to be
random or even uniform if the individuals of the population have a tendency to form
groups of certain size viz. vegetative clones in plants or groups in animals. Depending
upon the distribution of groups, clumped distribution may therefore, be
•
a. Random clumped (groups randomly distributed)
b. Uniform clumped (groups uniformly distributed) or
c. Aggregated clumped (groups aggregated among themselves).
21. Environmental factors
affecting growth and yield
• Temperature
• Light
• Light intensity
• Light quality
• Light duration
• Water
• Chemical stimulants and inhibitors
• Pollutants
• Oxygen supply
• Ionizing radiation
• Nutrition supply
• Soil structure and composition of soil air
• Soil reaction
• Biotic factors
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22. • Temperature - The growth of plant occurs in the
range of about 0 to 35 oC. Within most of this range,
raising the temperature by 10 oC increases the growth
by 2-3 times. There are three temperatures known as the
cardinal points for growth, the minimum or the lowest
temperature at which growth can be detected; the
optimum or temperature of maximum range of growth;
and the maximum or the highest temperature at which
growth can be detected. These are not very sharp
temperatures and they vary from species to species.
23.
24. • Light – although growth of higher plants eventually
depends upon photosynthesis, light as such is not essential
for the process of plant growth as long as sufficient amount
of organic materials are available. Some plants can complete
their life cycle in the dark e.g. tuberous or bulbous plants.
The higher plants grow in dark show a weak growth known
as etiolation. Usually the leaves remain free of
chlorophyll and the colour is therefore pale yellow,
although some ferns, gymnosperms, seedlings and algae can
synthesize chlorophyll in the dark. Light effects variously
and depends upon its intensity, quality and periodicity.
25. •
• Light intensity – Weak light promotes shortening of internodes and
expansion of leaf. Very weak light reduces the rate of overall growth and
also photosynthesis. Development of chlorophyll is dependent on light and
in its absence etiolin compound is formed which gives yellow colour to the
plant. Similarly high light intensity affecting indirectly increases the rate of
water loss and reduces the rate of growth.
•
• Light quality – Different wavelengths of light affect the growth of plant.
Blue violet light enhances the intermodal growth while green light
reduces the expansion of leaves as compared with complete spectrum of
visible light. Red light favours growth. Infrared and ultraviolet lights are
detrimental to growth.
•
• Light duration – Duration of light remarkably affects vegetative as well
as reproductive structures. The induction and suppression of flowers are
dependent on duration.
