Page 55 - soil-plant-water relationship and water requirement

SOIL-PLANT-WATER RELATIONSHIP AND WATER REQUIREMENT

Where,
GIR – Gross Irrigation Requirement
FIR – Field Irrigation Requirement
TL – Transportation Losses

The gross irrigation requirement can be determined for a field, for a farm, for
an outlet command area, and for an irrigation project, depending on the need
by considering the approximate losses at various stages of crop.

Figure 5.5.2-1: Relation of NIR,FIR and GIR

All the quantities are usually expressed in terms of water depth per unit of land
area (ha/cm) or unit of depth (cm).

5.5.3 Irrigation Scheduling

In order to prepare schedule of irrigation it is necessary to decide the time
interval between successive irrigations.

Irrigation scheduling is essential for good water management and it deals with
two classical questions related to irrigation. These are

 How much to irrigate and
 How often to irrigate.

How often and how to irrigate is function of irrigation water needs of the crop.

For example, if irrigation water need of crop is 5 mm/day, each day crop needs
a water layer of 5 mm over the whole cropped area. However, 5 mm of water
need not be supplied every day.

Generally, drips irrigation systems are designed to meet irrigation water
requirement on daily or at an interval of 2-3 day days. However, longer gap
between irrigations is maintained in other irrigation system.

In any case, irrigation interval is chosen such that crop does not suffers from
water tress.

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