Water requirement of crops-Water Resource Engineering

Water requirement of crops

Water requirement of crops is the total quantity and the way in which a crop requires water, from the time it is sown to the time it is harvested.The water is the essential constituent for plant growth.Vary with the crop as well as with the place .

Different crops will have different water requirements,& same crop may have different water requirements at different places of the same country.There are different sources of water.The movement of water in the environment depends upon hydrologic cycle.

Depend on

  • Climate
  • Type of soil
  • Method of cultivation
  • Useful rainfall

Water requirement of crops


Crop period

The time period that elapses from the instant of its sowing to the instant of its harvesting

Base period or Base of the crop

The time between the first watering of a crop at the time of its sowing to its last watering before harvesting.Crop period is slightly more than the base period.All practical purposes, they are taken as one and the same thing, and generally expressed in days.It is represented by B.

Duty and Delta of a crop

The delta and duty are the major factors in Water requirement of crops.


Each crop requires a certain amount of water after a certain fixed interval of time, throughout its period of growth. Depth of water required every time, generally varies from 5 to 10 cm depending on the type of crop.If the depth of water is required five times during the base period, then the total water required by the crop for its full growth , will be 5 multiplied by each time depth

The total quantity of water required by the crop for its full growth

Expressed in hectare-metre (Acre-ft) or in million cubic metres (million cubic ft)

The total depth of water (in cm) required by a crop to come maturity is called its delta (Δ )

Duty of water

Relationship between the volume of water and the area of crop it matures. This volume of water is generally expressed by : a Unit discharge flowing for a time equal to the base period of the crop, called base of a duty.

Relation b/n area of crop irrigated and the quantity of irrigation water required during the entire period of the growth of that crop

If water flowing at a rate of one cubic metre per second, runs continuously for B days, and matures 200 hectares, then the duty of water for that particular crop will be defined as 200 hectares per cumec to the base of B days

Duty is defined as the area irrigated per cumec of discharge running for base period B

Duty is represented by D

Relation b/n duty and delta

Let there be a crop of base period B days

Let one cumec of water be applied to this crop on the field for B days
Volume of water @ 1m3sec in one day = 1×24*60*60 = 86400 m3

Now the volume of water applied to this crop during B days = V=1×24*60*60 *B= 86400B m3

By definition of duty(D), one cubic metre supplied for B days, matures D hectares of land This quantity of water (V) matures D hectares of land or 10∧4 D sq m of area

Total depth of water applied on this land=Volume /Area

By definition , total depth of water is called delta=86,400B/10­∧4

  = 8.64B/D In meteres = 864 × B/D in cm.


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