Soil water relationship and importent role in plants .
1. IMPORTANCE OF SOIL WATER -
Water an excellent worker for most of the plant nutrients, is a primary requisite for plant grow.
Water serves for functions in plants it is the major constituent of plant
people 85-99, is essemial for photosynthesis and conversion of starch to sugar.
The solvent in which nutrients move into and through plant parts, and it provides
plant turgidity, which must the proper form and position of plant parts to capture sunlight.
In fact, the soil water is a great realtor of physical, chemical and biological activities is soilthebp .
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| Soil water |
STRUCTURE OF WATER -
Water can participate in a series of reactions occurring in soils and plants, only because of
its structural behaviour. Water is simple compound, its individual molecules containing
One atom and two much smaller hydrogen atoms.
The elements are bonded togethercovalently, each hydrogen or proton sharing its single electron with the oxygen.
Insted of the atbeing arranged linearly (H-O-H) the hydrogen atoms are attached to the oxygen.
Water structure
Heat of solution-
Who loso of body do theis known as heat of solution.
Head of wetting -
When clay particles as hydrated cenain amount of energy must be
released and this phenomina is known as heat of wetting.
4. SOIL WATER ENERGY CONCEPTS -
The retention and movement of water in its uptake and translocation in plant and potentialevapo-transpiration etc. are also related e to
energy.
5- CLASSIFICATION OF SOIL WATER
There are generally two types of soil water classification based on drying of wet soil
growing plants therein. (A) physical and) biological.
A. Physical Classification
Under physical classification soil water is grouped into three on the basis of retentiongravitational, capillary and hygroscopic water.
Gravitational water.
Gravitational water may be defined as the water that is held at a potentialgreater than-1/3 bat and that portion of the soil water that will drain freely from the soil by the force of gravity.
Gravitational water is of little use to plants water
occupies the larger pores resulting poor aeration.
Therefore, the removal of excess water is a must for the growth of most plants.
Capillary water-
Capillary water is held in the microspore of soil (capillary pores) .
Capillary water held by
water is retained on the soil particles by force of attraction between soil partical and water molecules .
Capillary water may be defined as the water that is retained in the soil
on the water potential of 1/3 bar to -31bars.
The force of retention of water
by the soil particle is high and part of water is available and part of it is unavailable and so all capillary water is not available to plants.
Hygroscopic water -
Hygroscopic water is defined as the water that is held by the soil particles
at suction of more than -31bars .
It is essentially non liquid and movies
primarity in the vapour form.
This water is held niously that plants are not able to absorb it and
theory unavailable to plants .
Some microorganisms can live much form of water.
B. Biological Classification-
There is a definite relationship between moisture retention and its utilization by plants.
Biological classification is based on the availability of soil moisture to the plant.
Soil water under this system of classification can be divided into three categories.
Available water-
Available water is defined as that portion of water which is retained
in the soil between field capacity and the permanent wilting coefficient (-15 bars).
This water is easily usable by plants and therefore, it is called plant available water.
Unavailable Water-
Unavailable water is defined as the water which is held at soil
water potential greater than -15 bars. It is unavailable to plants.
It includes the whole of the
hygroscopic water plus a part of the capillary water below the wilting point.
Superfluous water-
is defined as the water which is retained in
the soil beyond the field capacity soil moisture tension. This water includes gravitational
water plus a portion of capillary water removed from large interstices. Such type of water
is unavailable to plants and rather presence of such water in the soil for a long period causes
harmful effect for plant growth because of lack of air
Hygroscopic coefficient-
Hygroscopic coefficient is determined by placing an air-dry
soil in a nearly saturated atmosphere at 25°C until soil absorbs no more water.
Wilting coefficient.
Sometimes i is also used as permanemt wilting point
per is defined as that of which is held potential less than-15 bars and it is
held strongly that plants are not able to absorb.
condition is sometimes recovered with the addition of water and it is then called temporary
wiring point, while such wilting condition of the plast is not recovered in spine of addition
of water and the is called permanent wilting point Both the wilting points indicate low moisture.
Field capacity-
Feld capacity is defined as the capacity of a soil at the bowd pull of the force of gravity and moisture is held with soda water
rental less than-1/3 bar isd to determine the amount of irrigation water needed the amount of reserve
Soil water as vailable to plant .
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