Surface irrigation system
- Water is applied to the soil surface from a channel located at the uppermost of the field.
- Water may be distributed to the crops in controlled flooding and uncontrolled flooding.
- Water is applied on the soil depends upon topography, texture, type of crop grown, quality and quantity of available water, source of available water and energy and labour required for irrigation
Surface irrigation can be applied in the following methods:
1) Uncontrolled flooding: This is most primitive and wasteful method of irrigation. It is followed in areas where unlimited water is available and a vast area like pasture is to be irrigated. In this method water is let into the field from the higher gradient and spread slowly all over the cropped area depending upon the slope.
Limitation
1) Greater loss of water and nutrients
2) More soil erosion
3) Depth of irrigation varies from place to place due to varied topography.
4) Greater percolation in certain pockets.
2) Controlled flooding: In this method of irrigation field plots, which are to be irrigated are divided into several plots convenient sizes of more or less even surface. The water is let into the field through main and sub channels for irrigation plot one after another. The different methods of controlled flooding are given as under:
a) Check basin method: Check basin method is applied in those areas where small stream of water is available, ground is nicely leveled and the crop needs a careful distribution of water. Bunds are constructed around the area forming basin within which the irrigation water can be controlled. The water is conveyed through main channel and branch channels which used to connect two consecutive parallel rows of beds or basins. Rectangular or square beds of 10-100 m2 areas are prepared. The basins are filled to the desire depth and the water is retained until infiltrate. Crops like onion, garlic; rice can be irrigated by this method.
Merits
i) Different kinds of crops can be grown in sequence in the same field without making major changes in design, layout or operating procedure.
ii) Check basins are useful when leaching is required to remove salts from soil profiles.
iii) This method usually results in high water application and distribution efficiency.
iv) This method enables the conservation of rainfall and reduction in soil erosion by retaining a large part of the rain in the basin to be infiltrated gradually, without loss due to surface runoff.
Demerits
i) Very expensive as preparation of ridges for making channels.
ii) Fairly large area is occupied by ridges and channels which remain uncropped.
iii) Ridges interfere in movement of animal drawn or tractor drawn implements for inter culture or harvesting of the crops.
iv) Precise land grading and shaping are required.
v) This method is not suitable for irrigated crops which are sensitive to wet soil conditions around the stem of plants.
b) Border strip method
In this method the field is divided into a number of long parallel strips called borders that are separated by two ridges. This method is suitable in areas having a slope of 0.5-1.0%. The width of strip may be 3-15 m and length may be 50-300 m, which depends upon type of soil and extent of slope exceeds 1% slope the contour borders are prepared. The border method is suitable for irrigating all close growing crops lime wheat, barley, fodder crops and legumes. Straight borders are suitable when land slope exceeds the safe limits; if fields are undulating and leveling is not feasible then the border method is suitable.
Merits
i) Border ridges are easily constructed with simple farm tools.
ii) Labour requirement is greatly reduced.
iii) Uniform distribution of water is maintained with higher application efficiency.
iv) Operation system is easy and simple.
v) Surface drainage can be easily made from the cross ridges.
vi) This method is more suitable to the soils having moderately low to moderately high infiltration rates.
Demerits
- It is not suitable for those crops which require water stagnation throughout their cropping period e.g. rice, jute etc.
- This method is not suitable in sloppy and undulated land areas and having coarse sandy soils (having high infiltration rates).
- It is also not well suited to soils having very low infiltration rates.
c) Furrow irrigation method: This method is generally used for those crops which are sensitive to saturated conditions at the root zone, these are root and tuber crops. It is adopted for irrigated row crops where furrow made between the crop plant during the land preparation and planting. The crop is sown on the ridges and the irrigation water is applied in the furrow so that most of the roots remain above the saturation zone and there is no soil compaction. Field is divided into ridge and furrows along or across the slope and the furrows are connected with main channels. Sometimes ‘V’ shaped furrows are prepared along the slope of the land which are called corrugated or corrugation method of irrigation. The length of time, the water is to flow in furrows depends on the amount of water required to replenish the root zone and the infiltration rate of the soil and the lateral spread of water in the soil.
Merits
- Water in the furrows contacts only one half to one fifth of land surface, thereby reducing puddling and crusting of the soil, and evaporation losses.
- Earlier cultivation is possible which is a distinct advantage in heavy soils.
- The labor requirements in land preparation and irrigation is greatly reduced.
- No wastage of land in field ditches.
d) Ring basin method of irrigation
Ring method of irrigation is generally applied to widely spaced crops where limited stream of water is available for irrigation. A ring is prepared around each plant and each row of rings is connected with each other through main channel which is prepared at the end of the row of rings. Rings may smaller during the early stage but the size increases as the plant grows.
