Factor Effecting Duty

The duty of water of canal system depends upon varieties of factors. The principal factors are as follows:

• Methods and system of irrigation : In the perennial irrigation system, soil is continuously kept moist, and hence water required for initial saturation is less. Also, due to the shallow depth of water table, deep percolation losses are less. In the inundation irrigation, there is wasteful use of water. Hence, the perennial irrigation system has more duty than the inundation irrigation. The flow irrigation system has lower duty due to the conveyance losses in the network of the canals, while the lift irrigation system has higher duty because the command area of each well is very near to it. Tank irrigation gives high duty dur to rigid control.

• Mode of Applying Water : The flood irrigation system has lesser duty than the furrow system. Sub-irrigation system gives still higher duty. The ring basin irrigation and uncontrolled flooding give less duty.

• Mode of Cultivation : If the land is properly ploughed and made quite loose before irrigating, soil will have high water retention capacity in its unsaturated zone. Thus, the number of waterings can be reduced, increasing the duty. The old and the convention methods of cultivation gives less duty in comparison to modern method.

• Time and frequency of Tilling : Frequency of cultivation reduces the loss of moisture through weeds. Soil structure affects the plant growth to a very great extent. A structure (i.e. the good arrangement of soil particles in relation to one another) is called good tilth of soil. When the soil is in good tilth, evaporation losses from the surface of soil is less, soil becomes properly aerated, and hence yield of the crop is better.

• Type of the crop : The duty varies from crop to crop.

• Base period of the crop : If the base period of the crop is more, the amount of water required is high, hence duty will be low.

• Climatic condition of area : The climatic condition which effects the duty are temperature, wind, humidity and rainfall. Due the high temperature and wind, evaporation losses will be more and the duty will be less. A humid atmosphere reduces the losses. Rainfall during the crop period will reduce the irrigation water requirement and the duty will thus be higher.

• Quality of water : If harmful salt content and alkali content of the water is more, water will to be applied liberally so that the salts are leached off. This will, in turn, reduce the duty.

• Method of assessment of water : Volumetric method of assessment always leads to higher duty. This is because the farmer will use the water economically. If, however, the method of assessment is based on area under cultivation, the farmer has a tendency to use more water, and the duty will be low.

• Canal Conditions : In an earthen canal, seepage and percolation losses will be high, resulting in low duty. If, however, the canal is lined, the losses will be less, and the duty will be high.

• Character of soil and sub soil of the canal : If the canal is unlined and if it flows through coarse grained, permeable soils, the seepage and the percolation losses will be high. If the canal flows through fine grained soil, such losses will be less and the duty will be higher.

• Character of soil and sub soil of the irrigation fields : If the soil and the sub-soil of the fields will be coarse grained, percolation losses will be high. However, if there is hard pan at depth 1 to 2 metre below the surface, the percolation loss reduces. The duty is also affected by the topography of the land. If the field is not level, the lower portions get more water, while the higher portions may remain drier. In order to supply water to the higher places, more water will be used, and the duty will be reduced.

Methods of Improving Duty

When once the various factors affecting duty are properly understood, the duty can be improved by making those factors less effective which tends to reduce the duty.

1. Suitable method of applying water to the crops should be used.
2. The land should be properly ploughed and levelled before sowing the crops. It should be given good tilth.
3. The land should be cultivated frequently, since the frequent cultivation reduces loss of moisture specially when the ground is within the capillary reach of ground surface.
4. The canals should be lined. This reduces percolation and seepage losses. Also, water can be conveyed quickly, thus reducing evaporation losses.
5. Parallel canals should be constructed. If there are two canals running side by side, the F.S.L will be lowered, and the losses will be reduced.
6. The idle length of canal should be reduced.
7. The alignment of the canal in sandy soil and fissured rock should be avoided.
8. The canals should be so aligned that the area to be cultivated are concentrated along it.
9. The source of the supply should be such that it gives good quality of water.
10. The rotation of the crop must be practised.
11. Volumetric method of assessment should be used.
12. The farmers must be trained in the proper use of water, so that they apply correct quantity of water at the correct timing.
13. The land should be redistributed to the farmers so that they get only as much land as they are capable of managing it.
14. Research station should be established in various localities to study the soil, the seed and the conservation of moisture.
15. The canals administrative staff should be efficient, responsible and honest. The operation of canals should be such that the farmers both at the head as well as at the tail end get water as and when they need.