Page 49 - soil-plant-water relationship and water requirement

SOIL-PLANT-WATER RELATIONSHIP AND WATER REQUIREMENT

 Amount of weather used by plants (WP) for its metabolic activities which
is estimated as less than 1% of the total water absorption. These
three components cannot be separated so easily. Hence the ET loss is taken
as crop water use or crop water consumptive use.
 Other application losses are conveyance loss, percolation loss, runoff
loss, etc., (WL).
 The water required for special purposes (WSP) like puddling
operation, ploughing operation, land preparation, leaching, requirement, for
the purpose of weeding, for dissolving fertilizer and chemical, etc.

Crop Water Requirement is symbolically represented as:

WR = T + E + WP + WL + WSP

(The other application losses and special purposes are mostly indented for wet land
cultivation. Hence for irrigated dry land crop the ET loss alone is accounted for crop
water requirement).

The estimations of the water requirement of crop are one of the basic needs for crop
planning on the farm and for the planning of any irrigation project. This crop water
requirement is also needed to decide the stream size and design the canal capacity.
Water requirement may be defined as the quantity of water required by a crop or
diversified pattern of crop in a given period of time for its normal growth under field
conditions at a place.

Water requirement includes the losses due to ET or CU and losses during the application
of irrigation water and the quantity of water required for special purposes or operations
such as land preparation, transplanting, leaching etc., Hence it may be formulated as
follows

WR = ET or Cu + application loss + water for special needs.

It can also be stated based on “Demand” and “supply source” as follows

WR = IR + ER + S

Where,

IR - Irrigation requirement
ER - Effective rainfall
S - Contribution from ground water table.

Hence the idea about crop water requirement is essential for farm planning with respect
to total quantity of water needed and its efficient use for various cropping schemes of
the farm or project area. This crop water requirement is also needed to decide the
stream size and design the canal capacity.

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