Question

The ratio of the quantity of water stored in root zoon of the crops to the quantity of water actually delivered in the field is termed as

Answer 1

Water Requirements of Crops

Every crop requires a certain quantity of water after a certain fixed interval, throughout its period of growth. If natural rain is sufficient and timely so as to satisfy both these requirements, no irrigation water is required for raising that crop.

In a tropical country like India, the natural rainfall is either insufficient, or the water does not fall frequency of the rainfall varies throughout a tropical country, certain crop may require irrigation in certain part of the country .The area where irrigation is a must for agriculture is called the arid region, while the area in which inferior crops can be grown without irrigation is called a semiarid region.

Crop Period or Base Period

The time period that elapses from the instant of its sowing to the instant of its harvesting is called the crop period. 

The time between the first watering of a crop at the time of its sowing to its last watering before harvesting is called the base period or the base of the crop.

Crop period is slightly more than the base period, but for all practical purposes, they are taken as one and the same thing, and generally expressed in days. 

Delta of a Crop (Δ)

Each crop requires a certain amount of water after a certain fixed interval of time, throughout its period of growth.

The total quantity of water required by the crop for its full growth may be expressed in hectare metre (ha.m) or simply as depth to which water would stand on the irrigated area if the total quantity supplied were to stand above the surface without percolation or evaporation. This total depth of water (in cm) required by a crop to come to maturity is called its delta (Δ).

Explanation- The depth of water required every time, generally varies from 5 to 10 cm depending upon the type of the crop. If this 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 final figure will represent the total quantity of water required by the crop for its full-fledged nourishment.

Example: If rice requires about 10cm depth of water at an average interval of about 10 days, and the crop period for rice is 120 days, find out the delta for rice.

Solution: Water is required at an interval of 10 days for a period of 120 days. It evidently means that 12 no. of waterings are required, and each time, 10 cm depth of water is required. Therefore, total depth of water required.

 = 12 x10 cm = 120 cm.

Hence Δ for rice = 120 cm. Ans.

Example: If wheat requires about 7.5 cm of water after every 28 days, and the base period for wheat is 140 days, find out the value of delta for wheat.

Solution: Assuming the base period to be representing the crop period, as per usual practice, we can easily infer that the water is required at an average interval of 28 days up to a total period of 140days.

This means that 5(140/28) no. of waterings are required 28days

The depth of water required each time = 7.5 cm.

Total depth of water required. In 140 days = 5 x7.5 = 37.5 cm

Hence, Δfor wheat = 37.5 cm. Ans.

 

Delta for certain crops

The average values of deltas for certain crops are shown in table. These values represent the total water requirement of the crops. The actual requirement of irrigation water may be less, depending upon the useful rainfall. Moreover, these values represent the values on field, i.e. ‘delta on field’ which includes losses.