Systems of irrigation

Various types of irrigation techniques differ in how the water obtained from the source is
distributed within the field. In general, the goal is to supply the entire field uniformly with
water, so that each plant has the amount of water it needs, neither too much nor too little. The various irrigation techniques are as under:
i) Surface irrigation
ii) Sub-surface irrigation
1) Surface irrigation:-
a) Flow irrigation
b) Lift irrigation
When the water is available at a higher level and it is supplied to lower level by the mere
action gravity, then it is called flow irrigation. But if the water is lifted up by some mechanical (or) manual means such as by pumps etc. and then supplied for irrigation then it is called Lift irrigation. Use of wells and tube wells for supplying water for irrigation falls under the category of Lift irrigation.
Flow irrigation:-

Perennial irrigation

Flood irrigation

Perennial Irrigation: In perennial system of irrigation constant and continuous water supply is assure to the crops in accordance with the requirements of the crop throughout the crop period. In this system of irrigation water is supplied through canal distribution system taking off above a weir or a reservoir. When irrigation is done by diverting the river runoff into the main canal by constructing a diversion weir or a barrage across the river then it is called direct irrigation but if a dam is constructed across a river to store water during monsoons so as to water in the off taking channel during periods of low flow.
Flood Irrigation: Flood irrigation is also known as inundation irrigation. In this method of irrigation soil is kept submerged and thoroughly flooded with water so as to cause thorough saturation of the land. The moisture soaked by the soil when occasionally supplemented by natural rainfall (or) minor watering.
2) Sub surface irrigation: It is termed as sub surface irrigation because in this type of irrigation water does not wet the soil surface. The underground water nourishes the plant roots by capillary. It may be divided into the following two types.

Natural sub irrigation

Artificial sub irrigation

Natural sub irrigation: Leakage water from channels etc. goes underground and during passing through the sub soil it may irrigate crops sown on lower lands by capillary.
Artificial sub irrigation: When a system of open joined drains is artificially laid below the soil so as to apply water to the crops by capillary then it is known as artificial sub irrigation
Various techniques of distribution of water in the farms:-
a. Flooding irrigation
b. Drip irrigation
c. Furrow irrigation
d. Sprinkler irrigation
Flooding irrigation methods:

Free flooding method

Basin flooding method

Border flooding method

Check flooding method

Free flooding method: In this method ditches are excavated in the field, and they may be either on the contour or up and down of the slope . Water from these ditches, flow across the field. After water leaves the ditches no attempt is made to control the flow. Since the movement of water is not controlled, it is sometimes called wild flooding. Although the initial cost is low, labour requirement are usually high and water application efficiency is also low. This type is suitable for close growing crops etc., particularly where the land is steep. Contour ditches, are generally spaced at about 20 to 50 m apart.
Border flooding method: In this method, the land is divided into number of strips, separated by low levees called borders. The land areas confined in each strips is of the order of 10 to 20 m in width and 100 and 400 m in length. Ridges between borders should be sufficiently high to prevent overtopping during irrigation. To prevent water from concentrating on either side of the border, the land should be levelled perpendicular to the flow. Water is made to flow from the supply ditch into each strip. The water slowly towards the lower end and infiltrates into the soil ass it advances. When the advancing water reaches the lower end of the strip, the supply of water to the strip is turned off.
Check flooding method: Check flooding is similar to ordinary flooding that the water is controlled by surrounding the check area low and flat levees. Levees are generally constructed along the contour, having vertical interval of about 5 to 10 cm. these levees are connected with cross levees at the convenient places. In this method, water at fairly high rate and allowed to stand until the water infilitrates. This method is suitable for permeable and non permeable soil.
Sprinkler irrigation method: In this form water application method water applied to the soil in the form of spray through a network of pipes and pumps. Is kind of an artificial rain and therefore gives very good results. It is costly process and widely used in U.S.A. It can be used for all type of soils and for widely used in all topography and slopes. It can advantageously be used for many crops, because it fulfils the normal requirement of uniform distribution of water. In this method is very suitable for irrigation area in Rajasthan in India, where other type of irrigation are very difficult. In spite of the numerous advantages which this method over other methods. It has not become popular in India for the simple reason that occurs in a poor and developing nation. This method is only costly but requires lot technicalities. The correct design and efficient operation are very important for the success of this method.
Types of Sprinkler system are classified under three heads as
a. Permanent system
b. Semi-Permanent system
c. Portable system
Permanent system: The main pipes and lateral pipes are buried in the soil and they not interfere the farming operation.
Semi-Permanent system: The main pipes are buried in the soil and lateral pipe are portable.
Portable system: The main pipe and lateral pipes both are portable and the network can move from farm to farm.
Advantages of sprinkler irrigation
a) Seepage losses are completely eliminated.
b) Land leveling is not required.
c) No cultivation area is lost for making ditches.
d) Avoid surface run off.
e) Fertilizer can be uniformly applied.
f) Leaches down salt and prevent water logging or salinity.
g) It is labor oriented and 80% efficiency is achieved.
The limitation of sprinkler irrigation is
a. High wind may distort sprinkler pattern and non – uniform spreading of water on the crops.
b. In areas of high temperature and considerable evaporation losses of water may take place.
c. They are not suitable to crop requiring frequent and larger depths of irrigation irrigation such as paddy.
d. It require large electrical power
e. A constant supply water is needed for commercial use of equipment.
Drip/Trickle Irrigation Method: This system involves laying of a system of head, mains, sub mains, laterals and drop nozzles. Water oozes out of these small drip nozzles uniformly and at a very small rate directly into the plants root area. The head consists of a pump to lift power so as to produce the desired pressure of about 2.5 atmospheres for ensuring proper flow of water through the system. The lifted material like black PVC. These are generally buried or laid on the ground. There sizes should be sufficient to carry the design discharge of the systems. The laterals are very small sized (usually 1 to 1.25 cm) specially designed black PVC pipes taking off from the mains (or) sub mains. Laterals can usually be up to 59 m long and one lateral line is laid for each row of crops. Hardie Biwall is a patented name of dual chambered micro tubing manufactured from a linear low density polyethylene and is being used these days for laterals. The drip nozzles also called emitters (or) valves are fixed on laterals of about 0.5 to 1 m (or) discharging water at very small rates of the order 2 to 10 Liters per hour. Like the sprinkler system this method also involves specialized knowledge and is not being adopted by our ordinary farmers. This method is however being used for small nurseries, orchards or gardens. The widely known commercial Indian company which specializes in this field irrigation method is known as Jain irrigation systems Ltd. This firm can be contacted in special needs for layout of such an irrigation system.
Quality of Irrigation Water
The quality of irrigation water is very much influenced by the constituents of the soil which is to be irrigated. The various types of impurities which make the water unfit for irrigation, are classified as:
i) Sediment concentration in water
ii) Total concentration of soluble salts in water
iii) Proportion of sodium ions to other cat ions
iv) Concentration of potentially toxic elements present in water
v) Bicarbonate concentration as related to the concentration of calcium plus magnesium
vi) Bacterial contamination
Proportion of sodium ions to other cat ions
Most of soils contain Ca and Mg ions and small quantities of Na ions. The %of the Na ions is generally less than 5% of the total exchangeable cat-ions. If this % increases to about 10% or more, the aggregation of soil grains breaks down. The soil becomes less permeable and poorer tilth. It starts crusting when dry and its pH increases towards that of an alkaline soil. High Na soils are, therefore, plastic, sticky when wet, and are prone to form clods, and they crust on drying. The proportion of Na ions present in the soils is generally measured by a factor called Sodium-Absorption Ratio (SAR) and represents the Sodium hazards of water