Systems of Irrigation :

Several systems of Irrigation are in vogue to suit different crops, topography, soil types, water resources, climatic conditions and costs. The irrigation method should allow conservation of soil and should also provide enough water to satisfy the needs of plants but not cause waste and damage. These systems are :

A.

Flow
  i. Surface irrigation system
ii. Sub-soil irrigation system

B

 Sprinkler irrigation system

C

 Drip irrigation system.

A. Flow

Surface Irrigation system :

In this system, water is directly applied to the surface of the soil from conveyance system, channel or pipe located at the upper reaches of the field and spread by gravity flow incidental to the slope of the land. There are several methods in this system, the commonest being flooding, basin, border/ strip and furrow.

Flooding:

It is oldest and most primitive method of irrigation. flooding may be free flooding from the ditch, check flooding basin.

Merits:

Least cost method.
 

Does not require any skill.

Demerits:

Inefficient method
 

Result in ununiform stand of crop and low yield.
 

More wastage of water due to run off, deep seepage and evaporation.

Border Irrigation :

Irrigating a field by dividing it into number of strips, generally varying from 6 to 18 m, in width and 30 to 150 m in length and levelling the land and seperating the strips by earth bund about 30 cm., high is known as Strip method of Irrigation.

For moderate slope, of about 0.5 % , the following lengths are suggested:

    1. Sandy or sandy loam soils 30 m
    2. Medium silt loam soil 60 to 90 m.
    3. Clay loam or clay soil 90 to 150 m.

Merits:

i.   Uniform application of water.
 

ii.  Efficient use of water.

Demerits:

i.   The land needs to be graded uniformly

 

ii.  Requires repairing of ridges.
 

iii. Requires supervision during irrigation.

Basin:

It consists of letting water into level square plots of 3.6 x 3.6 m size surrounded by small bunds to retain desired depth of water.

Merits

 i. Suitable for all types of soil.
ii. Efficient use of water.

Demerits:

 i. Initial cost for leveling land is high.

Furrow Irrigation:

In row crops, furrows are made between the two crop ridges. The furrows can be made along the slope when the level of the land is sloping gently upto 3%. When slope exceeds upto 15% the furrows are laid out on graded counters or cross-slope furrows. The length of the furrows varies with the soil type, the slope and the quantity of the water to be applied.

Merits :

 i.Uniform application of water.
ii.Less evaporative losses.
iii.Less weed infestation
iv.Less intercultural operations.

Demerits

 i. Cost for preparing furrows is more. ii. Requires more labour.

Sub-soil irrigation:

In the sub soil irrigation system, water is applied into a series of field ditches deep down upto impervious layer. It then moves laterally and then vertically through capillaries and saturates the root-zone. A continous supply of moisture in the crop root-zone is, thus, assured from the artificial water-table conditions created by the ponding of irrigation water on the impervious layer. In artificial sub-irrigation, perforated or porous pipes are laid underground in the vicinity of the root-zone and water under pressure is distributed through these pipes. An impervious sub-soil at a depth of two metres or more, highly permeable loam or sandy-loam surface soil, uniform topographic conditions and moderate slopes favour sub-irrigation.

Merits:

a. Efficient use of water
 

b. Low evaporation losses

Demerits:

a. Initial investment and maintenance cost are high.
 

b. Not suitable for high rainfall areas


B. Sprinkler or Overhead Irrigation System:

In this system water is applied to the surface of any crop or soil in the form of a thin spray from above. A typical sprinkler system consists of a pump of lift and convey water under pressure, pipes or tubing of the conveyance of water, sprinkler heads or nozzles and risers which connect the sprinkler heads with a pipe line. Based on the equipments with which spraying is done, the sprinkler system has been classified as the rotating head type and the perforated head type.

The sprinkler system is also classified on the basis of portability of equipment as

  1. Portable
  2. Semiportable
  3. Stationary or permanent.

There are self-propelled sprinkler systems which move laterally or radically around a central pivot feeding-line. This portable system can be designed to cover any area ranging from three to four hectares to fifty to sixty hectares.

In aeroponic system nutrient solutions are sprinkled over the foliage in a regulated way. In mist chambers, phytotron and rhizotron irrigation is provided as aerosol droplets by sprinkling.

Merits
  1. Water application at controlled rate.
  2. Uniform distribution of water
  3. Highly efficient use of water.
  4. Suited to shallow sandy soils of uneven topography,
  5. Suited in areas where water and labour are scare.
  6. Suited in problematic soils.
  7. Application of fertilisers is possible.
  8. Used for cooling crops during high temperatures.
  9. Frost control during freezing temperatures.

Demerits:
  1. High initial costs.
  2. Require more maintenance

  3. High evaporatiopn losses.

 

C. Drip irrigation:

This system involves the slow application of water, drop by drop to the root-zone of a crop. The equipment consists of a pumping unit to create a pressure of about 2.5 kg/sq.cm, pipelines which may be of PVC tubing with drip type nozzles or emitters, and a filter unit to remove the suspended impurities in the water. The amount of water dripping from the nozzles can be regulated, as desired, by varying the pressure at the nozzles, and the size of the orifice of the nozzles. Water may be lifted and distributed through overhead pipe lines which are fitted with nipples to drop or trickle water to the desirable site or water may be held at a certain height from where it passes to the orifice which is impregnated into the root-zone.Water supply may be continuous or intermittent.

Merits:
  1. Very economic.
  2. Surface evaporation is reduced
  3. Suited to arid regions.
  4. Can be used for applying fertilisers.
  5. Increase yield by 50-60%

Demerits:
  1. Initial cost is more and
  2. Require high maintenance


Ag.
Technologies
(Water Mgmt.)