Plant Population Point Wise Notes for Competitive exam

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Plant Population

• Establishment of optimum plant population is essential to get maximum yield.

• In crops grown on stored soil moisture under rainfed conditions, population should not be high to deplete most of the moisture before crop matures and not low to leave moisture unutilized.

• Under conditions of sufficient soil moisture and nutrients, higher population is necessary to utilize other growth factors efficiently.

• If soil moisture and nutrients are not limiting, yield of crop is limited by solar radiation.

• Level of plant population should be such that maximum solar radiation is intercepted.

• Full yield potential of individual plant is achieved at wider spacing.

Yield per plant decreases gradually as plant population per unit area is increased, but yield per unit area is increased due to efficient utilization of resources.

Maximum yield per unit area is obtained when individual plants are subjected to severe competition.

• Plant height increases with increase in plant population due to competition for light.

• Sometimes moderate increase in plant population may not increase but decrease plant height due to competition for water and nutrients but not for light.

• Increase in plant height due to higher plant population is advantageous for better light interception due to exposure of individual leaves at wider vertical interval.

Leaf thickness increases with increase in plant density.

Leaf orientation is altered due to population pressure.

• Leaves are erect, narrow and are managed at longer vertical intervals under high plant densities.

Drymatter production per unit area increases with increase in plant population up to a limit when the reduction in the growth of a plant is more than compensated by increase in the number of plants per unit area.

• In indeterminate plants at higher plant density yield reduces due to reduction in number of ears.

• In determinate plants at higher plant density yield reduces due to reduction in size of ears or panicles.

Highly branching or tillering plants behave as indeterminate plants, and yield reduction is due to reduction in number of ears, pods etc.

• In non tillering or non-branching plants reduced yield is due to reduction in size of ears.

• Under very high population levels, plants become barren.

Holliday suggested two types of response curves, asymptotic and parabolic to quantify the relationship between plant population and yield.

ASYMPTOTIC RESPONSE

• In fodder crops where entire dry matter is the economic product or in tobacco where most of the dry matter is economic product, response to increasing plant density is asymptotic.

• In asymptotic response with increase in plant population after a limit, yield or dry matter does not decreases instead it remains constant.

• For fodder crops, dense stands are recommended to get maximum yield.

• Dense stands in fodder crops provides lean stems and more leafy fodder.

Asymptotic curve is expressed as follows Y = Ap + 1/1+Abp Y = Yield of dry matter/unit area A = Apparent maximum yield per plant P = number of plants per unit area b = linear regression coefficient

• Maximum yield obtained in particular situation when the plants are widely spaced with practically no competition is denoted as A or apparent maximum yield per plant.

• The term 1/1+Abp represents maxima in which maximum plant yield (A) is reduced by increasing competition resulting from greater plant density.

PARABOLIC RESPONSE:

• In crops where economic yield is a fraction of total dry matter, relationship between plant population and yield is expressed by parabolic curve.

• In parabolic response, yield increases with increase in plant population, then reaches maximum. With further increase in population yield decreases unlike asymptotic curve.

• Parabolic response can be fitted to quadratic equation. Y= a + bp + cp2 Y = Yield/unit area P = plant population a, b and c = regression coefficients

Drawback in representing parabolic response as quadratic equation is yield does not fall suddenly with increase in plant population, there is a plateau for some range of plant population depending on elasticity of plants.

Disadvantage of quadratic function can be overcome by square root function Y = a + bp + cp

• As density increases, the amount of drymatter in vegetative parts increases.

Economic yield increases with increase in plant population up to a point and subsequently decreases with increase in plant population.

Biological yield increases with increase in plant population up to a point and with further increase in plant population no additional biological yield can be obtained.

• Most important factors that influence optimum plant population are day length and temperature.

Photosensitive varieties respond to day length resulting in change in size of the plant.

Red gram plants sown as winter crop will have half the size of those grown in monsoon crops.

• Optimum population of monsoon season red gram is 55,000 plants/ha, whereas for winter crop it is 3.33 lakhs/ha.

• In winter as low temperature retards rate of growth, higher population is established for quicker ground cover.

• In sorghum, when climate is favourable during pre-anthesis period, optimum plant population is two lakh plants/ha, when climate is not congenial for growth during pre-anthesis it is four lakh plants/ha.

• In non tillering plants like maize, higher the fertility more should be the plant population to get higher yield.

• Increasing plant population increases the proportion of ears or fruits in the upper layer of canopy which facilitates ease in harvesting.

Cotton sown with a closer spacing, produces mostly sympodial branches and most of the bolls appear in the top layer of the canopy.

• With higher plant population, rice panicles appear in the upper layer of the canopy

Plant geometry refers to the shape of plant.

Crop geometry refers to the shape of space available for individual plants.

• Crop geometry is altered by changing inter and intra-row spacing.

Square arrangement of plants will be more efficient in the utilization of light, water and nutrients available to the individual plants than in rectangular arrangement.

• In wheat, decreasing inter-row spacing below the standard 15-12 cm i.e., reducing rectangularity, generally increases yield slightly.

• In crops like tobacco, intercultivation in both directions is possible in square planting and helps in effective control of weeds.

Groundnut sown with a spacing of 30 x 10 cm gave higher yield than same amount of population in square planting.

Pod yield is reduced either by increasing rectangularity or approaching towards square planting.

• Skipping of every alternate row is known as skip row planting.

• When one row is skipped, the population is adjusted by decreased intra-row spacing, it is known as paired-row planting.

• Skip row planting is generally resorted to introduce an intercrop.

Gap filling is not advantageous for short duration crops.

 

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