Dry Land Agriculture
Drought Adoptation
Drought Escape: Plants escape the drought due to their ephemeral characters
Drought Resistance:
Drought avoidance: “Ability to maintain a favourable water balance and
turgidity even when exposed to drought condition”
a). Water conservation
·
Stomatal
regulation
·
Increased
photosynthetic rate: Due to stomatal closure, C3 plants cannot satisfy
photosynthates need. But C4 plants do efficient photosynthesis even under low
carbon dioxide. So they are more drought tolerant. CAM
plants are very important drought tolerant crops. Since they open stomata in
night only, CO2 occurs in day. Presence of awn also increases the amount of
photosynthates
·
Reduction
of leaf area: by reduction in the leaf area, reduction tillering, leaf rolling,
parahelionastic movement of leaf, senescence and dropping of old leaves.
·
Thickness
of leaf cuticle, waxy surface, development of spines and pubescences.
·
Water
storage in plants
b). Improved water uptake.
·
Development
of roots
·
High
root and shoot ratio
·
High
liquid phase conductance
·
Osmotic
adjustment-breakdown of photosynthates-lower osmotic potential-development of
roots-ABA reduction
Drought tolerance
It differs from avoidance because
the plants here feel the water stress on plant parts and then overcome by their
morphological and physiological modification. So it is defined as “level of
stress at which 50 per cent of cells die”
a). Mitigating stress: Resistance to dehydration by having thick cuticle
and maintenance of high osmotic pressure.
b). High degree of tolerance: Avoids both metabolic train (CO2
and N2 assimilation) and plastic strain
Soil water dynamics
One of the best
methods to promote increase water availability for cultivation is by improving
the soil moisture storage. For that soil moisture dynamic should be understood
properly. It is defined as “change in soil moisture content with time”. These
changes can be grouped into
·
Run
off
·
Infiltration
and deep percolation
·
Redistribution
and storage
·
Evapo-transpirational
loss
There is no practical method to
improve the soil moisture storage, but it can be improved by changing the clay,
silt and organic matter content of the soil
Water Harvesting
Collection and storage of water on
land surface for subsequent use in arid and semi arid regions.
The difference between arid and
semi arid region in water harvesting are
Arid region
Catchment
area is bigger than Command area
Run
off is induced
Semiarid
Smaller
only excess water collected
Methods of water harvesting
Arid Regions
a). Run off Farming: Practiced in Negav desert of Israel
b). Water spreading: In arid regions, limited rainfall received in short
intense storms. So water swiftly drains into gullies, even affect the cropped
areas y flood due to sudden run off. Therefore, water is deliberately diverted
from the natural courses and spread over in adjacent plains. It uses check
dams, ditches, dukes and brush fences.
c). Microcatchment: Crops can be cultivated even with very low rainfall
if crop is surrounded by micro catchment basin.
Semi Arid region
a). Tanks: It consists of catchments area, tank bund, storage tank,
sluices, spillways and command area
b). Farm Ponds: 100-300m3 ponds dug in fields to collect run off water. The
main problem with farm pond is seepage loss. This can be controlled y
application of bentonite, soil depressant and soil cement mixtures.
c). Percolation tanks: Flowing rivulets/gullies are obstructed and
collected. It is as such raises water table due to percolation. So it can be
used for supplemental irrigation.
d). Inter row water harvesting
done in maize and sugarcane cultivation
e). Broad bed and furrow collects
excess water and diverted into farm ponds for later use.
f). Supplemental irrigation to
collect run off water.
Reducing evapo-transpiration loss
Evaporation is not directly
related to productivity so it should be prevented, transpiration also to some
extent should be controlled. ET can controlled by
Mulches: “any material applied on
soil surface to check evaporation and improve soil water.
·
It
improves soil water y reducing run off, interception of solar radiation,
prevention of evapo-transpiration, weed control and improvement in infiltration
·
Mulches
moderates soil temperature
·
It
controls soil salinity by increased infiltration and reduced evaporation
There are different types of
mulches used for this purpose. They include soil mulch, stubble mulch, plastic
mulch, vertical and straw mulch.
Antitranpirants: They prevent transpirational loss of water from the
plant surface
a). Stomatal closing type: They influence the plant to close
their stomata through which most of the water is lost. Ex. Phenyl Mercuric
Acetate, Atrazine
b). Film forming type: they are normally plastic and waxy materials used to
form film like coating on the plant surface. They allow the exchange of gases
but prevent the transpiration. The film should maintain continuity,
c). Reflectants: White coloured material which reflects light from the plant
surface. It reduces the leaf temperature, vapour pressure gradient from leaf to
atmosphere. Ex. 5% Kaolin, diatomaceous earth (Celite)
d). Growth retardants: It increases root growth and reduces shoot growth
and close stomata. Ex. Cycocel. Since they reduce the plant growth, they can
only be used under extreme moisture stress conditions.
Wind breaks and shelter belts
They prevent evaporation of water
from the soil and plant surface due to heavy winds. It also protects from wind
erosion and crop damages.
Weed control: One of the most important factors for the loss of
water from the soil surface is weeds. Therefore effective weed control is
important for effective water management.
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