Water Requirement of crops

Water Requirement of crops, Duty, Delta, Relation between duty and delta, Fectar affecting duty 

Water Requirement of crops:-

• Each crop requires a fixed amount of water after a certain fixed interval, throughout the crop period.
• In India, the natural rainfall is either insufficient or not regularly as required by crops.
• The magnitude as well as the frequency of the rainfall varies throughout the country.
• As the water requirement of crops not fulfil by rainfall then it requires irrigation.
• The area where irrigation is must for agriculture is called the Arid Region.
• The area where some crops can be grown without is called Semi-arid Region.
• The water requirement of the crop 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 requires will vary with the crops as well as with the place.
• The water requirement depends upon the variation in climate, types of soil, method of cultivation, and useful rainfall etc.

Crop Period or Base Period:-

• The time period between from the instant of its sowing to the instant of its harvesting is called the Crop period.
• The time period between the first watering of the crops at the time of its sowing to its last watering before harvesting is called Base period.
• Crop period is slightly more than Base period but they are taken as same.
• It is expressed in days.
• It is represented by B.

Delta of a crop:-

• It is denoted by Δ.
• Every crop requires a fixed amount of water at regular interval of time, throughout its Base period.
• The depth of water required in each irrigation, vary between 5 to 10 cm depending upon the types of crop, climate and soil.
• The time interval between two consecutive irrigations is called Frequency of irrigation or rotation period.
• The frequency of irrigation is expressed in days.
• The frequency of irrigation may vary between 6 to 15 days for different crops.
• It is the total depth of water required by the crop in irrigation at different interval of time, throughout its base period is called Delta of crop.
• The actual requirement of irrigation water may be less, depending upon the useful rainfall.
• Delta of crop includes the evaporation and percolation losses also.
• It is expressed in cm or m.

Duty of a crop:-

• It is denoted by D.
• The duty of water is the relationship between the volume of water and the area to be matures
• It is defined as the number of hectares of land that can be irrigated for full growth of a given crop by supplying of 1 m³/sec (one cumec) of water continuously during the entire base period of that crop.
• It is expressed in hectares per cumec.
• It is convenient in case of direct flow irrigation from canals, because by knowing the duty of water and the area of land to be irrigated for growing crop, the required discharge of canal can be determined.
• In case of tube well, the area which can be irrigated annually by the well is called the duty of well.
• If duty is expressed in hectares/million cubic metre of water available in the reservoir, then it is called Storage Duty.
• Duty of canal in direct irrigation is called Flow Duty.  
• It is expressed as hectares/cumec (ha/cumec or ha/m³/sec).

Relation between Duty and Delta:-

Let B is the base period of the crop. Let water is supplied to this crop on the field at a rate of one cumec for base period (B days).

The volume of water supplied to this crop in B days-

                                                         V = 1×60×60×24×B cubic metre

                                                            = 86400B cubic metre

Let D is the duty of water in hectare per cumec (or 10⁴ m2 per cumec), Δ is the total depth of water in metre supplied to the crop during the entire base period B days.

The total volume of water supplied to the crop-

                                                      V = D×Δ ha-m

                                                         = D×10⁴×Δ cubic metre

Hence, 

                                       D×10⁴×Δ = 1×60×60×24×B