Various methods can be used to supply irrigation
water to the plants
Surface irrigation is the application of water by gravity flow to the surface of the field.
•Either the entire field is flooded (Basin Irrigation) or the water is fed into small channels (furrows) or strips of land (borders).
•Basins are flat areas of land, surrounded by low bunds.
•The bunds prevent the water from flowing to the adjacent fields.
•Basin irrigation is commonly used for rice grown on flat lands or in terraces on hillsides. Paddy grows best when its roots are submerged in water. Hence, basin irrigation is the best method to use for this kind of crop.
•Trees can also be grown in basins, where one tree is usually located in the middle of a small basin.
•In general, the basin method is suitable for crops that are no affected by standing in water for longer periods.
•Basin irrigation is suitable for many field crops.
•Crops suitable for basin irrigation include pastures, citrus, banana and crops that are broadcasted such as cereals and to some extent row crops such as tobacco.
•Basin irrigation is generally not suited to crops, which cannot stand in wet or waterlogged conditions for periods longer than 24 hours; eg: potatoes, beet root and carrots
•The flatter the land surface, the easier it is to construct basins.
•It is also possible to construct basins on sloping land, even when the slope is quite steep. Level basins, called terraces, can be constructed like the steps of a staircase.
•Soils suitable for basin irrigation depend on the crop grown.
Basin should be small if the:
•Slope of the land is steep
•Soil is sandy
•Stream size to the basin is small
•Required depth of the irrigation application is small
•Field preparation is done by hand or animal power
Basin can be large if the:
•Slope of the land is gentle or flat
•Soil is clay
•Stream size to the basin is large •Required depth of the irrigation application is large
•Field preparation is mechanized
•The land slope, the soil type, the available stream size, the required depth of the irrigation application and farming practices mainly determine the shape and size of basins
•If the land slope is steep, the basin should be narrow; otherwise too much earth movement will be needed to obtain level basins.
•Three other factors, which may affect basin width, are depth of fertile soil, method of basin construction, agricultural practices.
•There are two methods to supply irrigation water to basins:
(i) The direct method: Irrigation water is led directly from the field channel into the basin through siphons, or bund breaks.
(ii) The cascade method: irrigation water is supplied to the highest terrace, and then allowed to flow to a lower terrace and so on.
Maintenance of basins
•Bunds are susceptible to erosion. This may be caused by, for example, rainfall, flood or the passing of people when used as footpaths.
•Rats may dig holes in the sides of the bunds.
•Therefore, it is important to check the bunds regularly, notice defects and repair them instantly, before greater damage is done.
Advantages of basin irrigation
•Conservation of rainfall and reduction in soil erosion.
•High water application and distribution eff iciencies.
•Useful in leaching of salts.
•Suitable to all close growing crops, row crops and orchards.
•Irrigation water flows from the field channel into the furrows by opening up the bank of the channel or by means of siphons or spiles.
•Furrows must be on consonance with the slope, soil type, stream size, irrigation depth, cultivation practice and field length.
•Uniform flat or gentle slopes are preferred for furrow irrigation.
•On undulating land, furrows should follow the land contours.
Advantages of furrow irrigation
•Suitable for row crops and vegetables.
•Suitable for soils in which the infiltration rates vary between 0.5 and 2.5 cm/hr.
•Ideal for slopes varying from 0.2 to 0.5 per cent and a stream size of 1-2 liters/sec.
•In areas requiring surface drainage or prone to temporary water logging, furrows are very effective.
•In areas where water for irrigation purposes. is scarce, the practice of alternate or skip furrow irrigation can save considerable quantity of water without significantly affecting yields.