Some Important Definitions & Irrigation Efficiency

 Some Important Definitions & Irrigation Efficiency

Crop Ratio:-

• The area to be irrigated for Rabi crop is generally more than that of Kharif crop.
• It is defined as the ratio of area to be irrigated in Kharif season to the area to be irrigated in Rabi season.
• It is also called Kharif-Rabi Ratio.
• This ratio is generally 1:2.
• Crop ratio should be selected such that the discharge of the canal is almost uniform in all season. So that full capacity of the canal can be utilized.

Paleo Irrigation:-

• In initial stages before the crop is sown, sometimes the land is very dry.
• This happens generally at the time sowing of Ravi crop.
• In dry land condition, the soil is irrigated, so as to help in sowing of the crop. This irrigation is known as Paleo Irrigation.
• It is irrigation done prior to the sowing of a crop.
• It adds sufficient moisture to the land which helps in the initial growth of a crop.
• It is done to prepare the land for sowing.

Kor Watering:-

• The first irrigation applied to the crops, when the crops have grown a few centimetres high, is called Kor-watering.
• The optimum depth of Kor-watering is different for different cops.
• The optimum depth of Kor-watering for Rice is greater than that for Wheat.
• The Kor-watering must be applied within a fixed time period, which is called Kor-period.
• The Kor-period depends upon the climate.
• The Kor-period for Rice is less than that for Wheat.

Cash Crops:-

• It is the crops which have to be encashed in the market for processing etc. as it cannot be consumed directly by the cultivators.
• All non-food crops are cash crops.
• Cash crops are- jute, tea, cotton, sugarcane, etc.
• Food crops are- rice, wheat, maize etc.

Crop Rotation:-

• The method of growing different crops in rotation, one after the other, in the same field, is called Crop rotation.
• Crop rotation will help in extracting different nutrient from the soil, and thus avoiding the general deficiency of any particular nutrient.
• It helps in increasing the fertility of soil.

Optimum Utilisation of Irrigation water:-  

• If a crop is grown under identical condition, with different water depths, the yield is found to be different.
• The yield increase with the increase of water, reach a certain maximum value and then falls down.
• The quantity of water at which the yield is maximum, called Optimum water depth.
• The supplies of water to the various crops should be adjusted in such a way as to get optimum benefit.
• The water supplied more than optimum water depth as well as less than optimum water depth reduces the crop yield.

                                                Fig.5.1.Optimum Utilisation of Irrigation water

Irrigation Efficiencies:-

• It is the ratio of the water output to the water input.
• It is expressed in percentage.
• The input of water minus output of water is called losses.
• If losses are more output is less and hence efficiency is less.
• Efficiency is inversely proportional to the losses.
• There are different kinds of efficiencies-

            1. Water Conveyance Efficiency

            2. Water Application Efficiency

            3. Water Storage Efficiency

            4. Water Use Efficiency

            5. Water Distribution Efficiency

            6. Consumptive Use Efficiency

1. Water Conveyance Efficiency:-

• It is denoted by η_c.
• It is the ratio of water delivered into the fields from the outlet of canal, to the water entering into the canal from the river or reservoir, at its starting point.
• It accounts for Conveyance or transit losses.
• It is calculated as-

                                                 

         Where, W_f  = Quantity of water delivered to the field

                      W_r = Quantity of water delivered into the canal system from the river or reservoir

 

2. Water Application Efficiency:-

• It is denoted by η_a.
• It is the ratio of the quantity of water stored into the root zone of the crops to the quantity of water actually delivered into the field.
• It is also called on-farm efficiency.
• It takes into consideration the water lost on the farm.
• The common sources of loss of water during its application to the field are surface runoff and deep percolation.
• It is calculated as-

    

OR

                     

            Where, W_s = Quantity of water stored in the root zone

                        W_f = Quantity of water delivered to the field

                        R_f = Quantity of water lost as surface runoff

                        D_f = Quantity of water lost as deep percolation

 

 3. Water Storage Efficiency:-

• It is denoted by η_s.
• It is the ratio of the water stored in the root zone during irrigation to the quantity of water needed to bring the water content of the soil to the field capacity.
• The water storage efficiency should be high in order to keep salts washed out when the soil has excess salts.
• It is calculated as-

           Where, W_s = Quantity of water stored in the root zone

                       W_n = Quantity of water needed to bring the water content of the soil to field capacity.

 

4. Water Use Efficiency:-

• It is denoted by η_u.
• It is the ratio of the water beneficially used by the crops including leaching water to the quantity of water delivered to the field.
• It is calculated as-

         Where, W_u = Quantity of water beneficially used by the crops

                     W_f = Quantity of water delivered to the field

5. Water Distribution Efficiency:-

• It is denoted by η_d.
• It is also called Uniformity Coefficient.
• The effectiveness of irrigation may also be measured by its Water Distribution Efficiency.
• When the water has penetrated to a uniformly throughout the field the deviation from the mean depth is zero and water distribution efficiency is 1.0.
• Higher the value of η_d, more uniformly is the water distributed in the root zone.
• It is determined by-

            Where D = Mean depth of water stored during irrigation

                        d = Average of the absolute values of deviations from the mean

6. Consumptive Use Efficiency:-

• It is denoted by η_cu.
• It is the ratio of the normal consumptive use of water to the net amount of water depleted from the root zone.
• It can be calculated as-

          Where W_cu = normal consumptive use of water or evapotranspiration

                      W_d = Amount of water depleted from the root zone