Unit - 6

Introduction to Irrigation

6.1 Definition

• It is the supply of water to the land or crop, to help growth typically by the means of channels.
• "It is an artificial application of water to the crops for assured production".
• “It is a controlled supply of water, as per the requirement of the crop".

Key Takeaways:

It is the supply of water to the land or crop, to help growth typically by the means of channels.

6.2 Function:

• The irrigation water dissolves the nutrients in the soil, which are required for the plant growth through roots.
• The irrigation water supplies moist to the soil. Which is required by the micro-life in the soil i.e., the de-composers in the eco-system.
• It helps to control the soil-temperature.
• It helps to soften the tillage pav i.e., the area to be irrigated.
• It provides a controlled and timely supply of water to be plant i.e., during sowing, growing and harvesting period.

Key Takeaways:

The irrigation water dissolves the nutrients in the soil, which are required for the plant growth through roots. The irrigation water supplies moist to the soil. Which is required by the micro-life in the soil i.e., the de-composers in the eco-system.

6.3 Advantages & Necessity:

Following are the advantages of irrigation:

1. The water is made available, when even required for the crops.
2. It has the controlled supply of water.
3. It can help to have more cropping season i.e., the summer crops are possible only through irrigation.
4. It helps to go for commercial crops.

6.4 Methods of Irrigation:

On the basis of the availability of water and source of water, the methods of irrigation vary as given below:

• A: Surface irrigation Methods
• B: Sprinkler Irrigation Methods
• C: Sub-surface or sub-irrigation Methods

6.4.1 Surface Irrigation:

• In these methods, the irrigation water is supplied to the field by spreading it either in a sheet or small stream forms.
• Three notable methods of surface irrigation, which again are sub-divided by the methods of spreading is applied either through the natural stream, by a paranal canal, taking the advantage of the natural slope of the land (gravity flow).
• This method is suitable for smooth and flat land. Where no pre-irrigation preparation is required. It is also applied to the lands having uneven and rough surface, if no other methods of irrigation are possible.
• This method is used in a region where the water to be used for irrigation is in abundance and cheap, because, a lot of water remains unused and so it has a lot of wastage of water. So, it is not an eco-friendly method of irrigation.

Key Takeaways:

In these methods, the irrigation water is supplied to the field by spreading it either in a sheet or small stream forms.

6.4.2 Subsurface Irrigation:

• In this method, the water is supplied to the plants, from below the surface by controlling the water table. It is given to the root zone of the plants.
• This method has two advantages, one as the water is directly provided to the roots of the plants, the evaporation loss is reduced and second. As the water is supplied from below there no need to have, borders, field channels or pipes etc. So maximum cultivable area is put under cultivation.

Methods of Sub-Surface Irrigation:

• The sub surface methods can be classified given below-

1. Natural Sub-irrigation.
2. Artificial Sub-irrigation.
3. Drip or Trickle irrigation.

Fig.: Sub-surface irrigation

Natural Sub-Irrigation:

• In this method the water is supplied to the crops by controlling the level of the water table.
• The method is called natural because, whatever water is received on the surface, gets percolated, through rivers, lakes streams drain and canals and reaches the water table which gets lifted upto the root zone of the crops and supplies the water for the growth of the plant. In this method to ensure the required supply of water for the growth of plants, the level of water table is required to be maintained by using artificial methods.
• For this a series of parallel channels with almost vertical sides are excavated in the fields which are to be irrigated.
• These channels are spaced about 15 to 100 metres from each after. This spacing depends upon the topography of the land and the permeability of the sub-soil. The depth of the channels varies between 0.3 and 1 metre and width between 0.25 and 0.5 metres. The beds of the channels are almost flat.
• The water is allowed to flow through these channels with very low velocity so, they always have enough water to get percolated in the sub soil and it helps to recipe the root zone of the crops.
• To prevent water logging conditions, it is necessary provide proper drainage to take out the excess amount of water. This can also be done by discontinuing the supply of water through the channels and by allowing the land to dry up, before harvesting.
• As the movement of water is always on upward side the water which comes up also brings salts and makes the soils saline and us less for cultivation, if it continues. So, there is need to have periodic leaching of soil, by applying more amount of water to get it percolated along the salts which have been brought up through the capillary actions.

Conditions Required to Apply Natural Sub Irrigation:

• The soil in the root zone must be loamy or sand-loam having maximum permeability.
• Below the surface at the depth of 2 to 3 metres there must be a free water table (developed, due to impermeable sub stratum.)
• The topographical conditions of the land to be irrigated must be uniform, with a flat surface.
• The water supply must be abundant and free from salts.
• It needs to have unusual natural conditions, so it is tried under different conditions', it may create unsafe conditions for the growth of the plants.

Artificial Sub-Irrigation:

• In this method, the water is applied beneath the land surface, by a network of buried perforated pipes. The water under pressure is allowed to percolate into the soil, to reach in the root zone of the plant and to provide the irrigation water for the growth
• The functioning of this method can be effective if the soil in the root zone has high horizontal permeability to permit free lateral movement of water and low vertical permeability to prevent deep percolation of water.
• To have uniform distribution of water which percolates in the soil the pipes are required to be very closely spaced (up to 0.45 metres space between two pipes).
• To avoid interference with the crops these pipes are buried at least 0.4 metres below the surface of the ground. The method is not commonly used due to the following limitations.

1. It is very expensive due high cost of pipes and the high installation charges as a skilled labour is required to lay down these pipes at a given depth.
2. As the rootlets tend to grow close to the outlets of the pipes, they clog the openings of the pipes and thus reduce the expected destruction of water and the performance of the pipe become very poor.

• To overcome these difficulties, mainly to avoid clogging of the small perforations, the water must be free from any type of silt sand or debris. The salinity of the water must be very low to avoid salinization of soil as in this method no laching is possible (to reduce the salinity of the soil.)

Drip or Trickle irrigation/Micro irrigation:

• This is one of the latest methods of irrigation and also a very popular method among the actual users of irrigation farming.
• In this method small diameter plastic pipes are used together with drip nozzles which are known as Emitters or Drippers. They deliver water to the land surface, near the base of the plant.
• In this method the application of water is at very low rate which varies between 2 and 10 lit/per hrs. This keeps the soil moisture within the desired range for growth of the plant.

Key Takeaways:

In this method, the water is supplied to the plants, from below the surface by controlling the water table. It is given to the root zone of the plants.

6.4.3 Micro Irrigation:

• This is one of the latest methods of irrigation and also a very popular method among the actual users of irrigation farming.
• In this method small diameter plastic pipes are used together with drip nozzles which are known as Emitters or Drippers. They deliver water to the land surface, near the base of the plant.
• In this method the application of water is at very low rate which varies between 2 and 10 lit/per hrs. This keeps the soil moisture within the desired range for growth of the plant.

Advantages of Micro-Irrigation:

• Drip irrigation or Micro-irrigation provides desired water and nutrients into the crop-root zones.
• It is ideal for a terrain with problematic soils and water resources.
• It saves the labour cost.
• It helps get higher yields.
• It saves water upto 70%.
• It is a custom-made irrigation system.
• It is an eco-friendly irrigation system, as it saves irrigations water.

Key Takeaways:

This is one of the latest methods of irrigation and also a very popular method among the actual users of irrigation farming.

6.5 Water Requirement of Crops:

• The total amount of water needed by a crop from the time of its sowing, up to the period of harvesting. If put together, the-sum total of water is known as "The water requirement of crop'.
• This quantity of water required by the crop varies from crop to crop, also varies from sowing harvesting period i.e., summer crops, winter crops, rainy season crops and naturally varies from soil to soil, depending upon the capacity of soil to retain the water i.e., higher the retaintivity less will be the amount of water needed to be supplied to the crop in that soil.
• For any crop, it is also necessary to maintain the quantity of readily available moisture in soil, by irrigation and so it is necessary to distribute the total amount of water required by any crop, in such a way that a part of it supplied at each irrigation, must be sufficient to meet the need of the crop, for a period in between two successive irrigation and is stored in the soil.
• So, together with the quantity of water required by the crop, it is necessary to calculate, the required frequency of irrigation and also the total quantity of water to be irrigated during each application. All these points (qualitative information) are based on the soil moisture conditions. Let us see what makes the conditions to retain the soil moisture.

Key Takeaways:

The total amount of water needed by a crop from the time of its sowing, up to the period of harvesting. If put together, the-sum total of water is known as "The water requirement of crop'.

6.6 Soil Moisture & Crop water relationship:

• It is known fact that the growth of most of crops is determined by either excessive or deficient amount of soil moisture contents. e.g., If excessive moisture is available in the soil, it fills the soil pores and aeration capacity of soil is reduced from the root zone.
• As the growth of the also depends upon the aeration, it affects the plant growth. On the other hand, if the soil has deficient amount of moisture, the soil in the root zone, holds it so tightly that the plants have to use an extra energy to get the moisture from the soil and it also affects the growth of the plant.
• If the rate of intake of moisture by the plant is not sufficient to maintain the turgidity of the leaves, this condition brings the permanent wilting point.
• So, between these two extreme moisture conditions, i.e., excessive moisture supply or deficient moisture supply there is a moisture content, which is designed as the optimum moisture content at which the growth of the plant is very rapid which finally results in the optimum growth of the crops.
• For most of the crops, this optimum moisture content is less than the field capacity of the soil (Refer Fig.).

Fig: Soil Moisture content

Key Takeaways:

It is known fact that the growth of most of crops is determined by either excessive or deficient amount of soil moisture contents. e.g., If excessive moisture is available in the soil, it fills the soil pores and aeration capacity of soil is reduced from the root zone.

6.7 Consumptive use of water

• "The total quality of water used for the plantation growth, of a given area, in transpiration and building of the plant tissues, and that evaporated from the soil in that area in a specific period of time is called as consumptive use of water or evapo-transpiration."
• So, this process includes not only the water (moisture) directly used by the plant but also the water removed from the soil by evaporation.
• Transpiration is a process, where in the water that enters the plant roots and which is used for the development of the plant tissues and finally which passes into the atmosphere in the form of vapour through its leaves.
• Evaporation is a process, where in the water from the soil passes into the air in the form of vapour; i.e., soil moisture is converted into the atmospheric moisture called as humidity.
• Dew, or the water drops of the rain water, settle for a short period of time on the leaves and get evaporated, after the day temperature rises. Though, these particles do not take part in the growth of the plants, still they are considered to be the part of consumptive use of water.
• This consumptive use is expressed in ha-m per hector or the depth of water in meters for a specified period of time, like a day, month or a cropping season (three or four months).
• As already discussed, the duty of water is used to express the water requirement of a crop and consumptive use also expresses the water requirement of the crop only. Between these two parameters, consumptive use of water is better parameter as it shown the accurate amount of water used (and required) by a crop.
• While the duty of water, includes the water lost by seepage, percolation and also evaporation (in the canal only), so that gives a general figure of the water requirement of the crop while consumptive use of water, considers only the water (moisture) used by the plant for its growth only.

Key Takeaways:

"The total quality of water used for the plantation growth, of a given area, in transpiration and building of the plant tissues, and that evaporated from the soil in that area in a specific period of time is called as consumptive use of water or evapo-transpiration."

6.8 Principal Indian crops: 

• The crops of any country depend upon various physical and climatic factors i.e. The types of soil, depth of soil, General slope of the region, Availability of water. Temperature condition and type of rainfall average rainfall, rainfall season etc.
• The type of crops also depends upon the economic conditions i.e., capacity to invest, need of the crops, transport facilities, market conditions etc. A country having a vast population to serve, needs to have food grains as a top, crop to be cultivated.
• India, we have a vast variation in all the physical and climatic factors e.g., south India has a tropical not and humid climate while in North India, it is sub-tropical, to temperature climate which is humid and cool. In Rajasthan and in Run of Kuch. It is dry climatic while in Assam, Meghalaya it is very humid climate.
• We receive the monsoonal type rainfall mainly due to south-west monsoons, which also have a huge regional variation i.e., coastal areas and states in the North-East directions observe heavy seasonal rainfall, while in the interior states and in western states rainfall is very low.
• The irrigational facilities also, make an impact on the selection of crops i.e., Uttar Pradesh, Bihar, Punjab, Haryana etc. states have good canal irrigation. So, the crops like wheat, Sugar cane cotton, oil seeds etc. are developed while in hot, dry region have lesser irrigation facilities, have dry non-irrigated crops mainly the food crops like, Jowar, Bajara, Rai, Pulses etc. Rice is cultivated in the stages having heavy rainfall. So west-Bengal, Odisha, Andhra Pradesh and Tamil Nadu have maximum are under Rice cultivation.
• So, India in general have high variation in the types of crops and also in cropping seasons i.e., Kharif and Rabi seasons the regions having good supply of irrigation water enjoy the third cropping season called as summer crops.

Key Takeaways:

The crops of any country depend upon various physical and climatic factors i.e. The types of soil, depth of soil, General slope of the region, Availability of water. Temperature condition and type of rainfall average rainfall, rainfall season etc.

6.9 Crop Season:

The Indian cropping season can be classified into two main season such as,

1. Kharif
2. Rabi

• This classification is based on the monsoon season i.e., South west monsoon and North-East monsoon.
• The Kharif cropping season is from July to October, during the S.W. Monsoon and the Rabi season is from October to March i.e., winter season. The crops which grown between March and June are called as summer crops.
• The Major Crops in India: The India crops can be classified by using different norms, as shown below:

Classification based on season:

1. Kharif crops,
2. Rabi crops
3. Summer crops

Classification Based on purpose of crops:

1. Food grains,
2. Fooder crops
3. Cash or Industrial crops

The classification based on the availability of water:

1. Rain fed crops
2. Irrigation crops

• The Important Kharip Crops: These crops are sown in the month of June after the arrival of S.W. Monsoon, rainfall. These crops include. Millets. i.e., Bajara and Jowar, Cotton, Soyabean, Sugarcane, Turmeric, Rice, Maize, Pulses (Moong), Groundnuts, Chillies etc.
• The important Rabi Crops: These crops are sown in the month of October i.e., in winter season. They are wheat, Barley, Mustard, Peas, Sesame etc.
• The Important Summer Crops: These crops are sown during the summer season i.e., between March and June. The main crops are vegetables, Muskmelon, Watermelon etc.

Key Takeaways:

The Indian cropping season can be classified into two main season such as,

1. Kharif
2. Rabi

6.10 Crop water requirement:

• How much water is required by a crop depends upon mainly factors, such as,

1. The type of crop
2. The cropping season
3. The duration of crop

• The short duration crops such as vegetables need lesser water but needs to have a controlled and assured water supply.
• The medium duration crop, e. General five-month crops, need lesser but assured water supply mainly for the crops during' non rainy season.
• The long duration crops i.e., the plantation crops need heavy water supply mainly through the controlled irrigation systems.

The Factors Influencing the Water Requirement of a Crop:

• Following are the important factors which affect the need of water for a crop

1. The annual average rainfall,
2. The rate of evaporation i.e., Temperature
3. The type of soil i.e., percolation
4. The growing season
5. The stage of plant growth
6. The sun-light
7. The wind velocity
8. The water availability
9. The quality of water

Key Takeaways:

How much water is required by a crop depends upon mainly factors, such as,

1. The type of crop
2. The cropping season
3. The duration of crop

6.11 Crop Planning:

• The fate of farmers in India, the determined by the rainfall as about 75% of the area under crop is served by rainfall i.e. no irrigational facilities are provided to these huge.
• Net Area sown 2015-2016, due to drought conditions, throughout India, the agriculture shuttered, with low to no yield, no food for persons and no fodder for the domestic animals, which created a very serious economic conditions in the rural parts of India.
• So, we need to have proper crop planning, mainly in the drought prone areas of India, extending from central and southern Rajasthan, central party of Madhya Pradesh, Marathwada Region of Maharashtra, central part of Andhra Pradesh upto the central parts of Karnataka.

The Crop Planning Methods:

• The Crop improvement Methods: In this method, new plants are introduced to a new area. This helps to improve the crops. It can be Inter-state as Intra-state.
• Acclimatization: It is an adaptation of an individual or a group of plant, under the changed climate. This helps to improve the crop.
• Mutation Breeding: The function of mutation with the help of mutagens is known as Mutagenesis. The commonly used chemical mutagens are Ethyl, Methane, Sulphonate (EMS) Ethylene imine (E.I.), Sodium azide. In India more than 300 varieties have been developed by using this Mutagenesis, namely BGM 408 (chick pea), Hans (Pea) JRO 3690 (Jute) Sharbati Sonora (Wheat). Jagannath (Rice) etc.
• The Tissue Culture: "The growth of tissues of living organism in a stable culture Mediuta Le in vitro is known as Tissue Culture This method has helped to improve the Toxicity resistance, Drought resistance.

Key Takeaways:

The fate of farmers in India, the determined by the rainfall as about 75% of the area under crop is served by rainfall i.e., no irrigational facilities are provided to these huge.

6.12 Agricultural Practices:

• The agriculture is the base or culture and has provided a sound occupation to the people in the rural areas and provides the 'food' to all the Indians. This age-old occupation has to face the following problems

1. It is based mainly on the S.W. Monsoons, so in case of drop the drought years the non-irrigated farming suffers.
2. The conventional seeds are used, so the yields and the total production of grains is lesser than the world average yields of these crops.
3. The investment capacity of the farmers is very low and hence they use the old techniques of farming.
4. The agricultural produce has a very high market fluctuations, so when the climate is better with the expected rainfall, the production i.e., supply goes above the market demand, to reduce the prices and when the demand is high, due to shortage of supply of the grains the farmers always suffer.
5. The export policy is not stable so when the local demand is less farmers wish to export but the central government, does not have the fixed rules for exports.
6. Due to law yields and low production the farmers as well as the landless labour or, migrate to cause problems to the urban areas and shortage of labour in the rural area.

Solutions

• To solve the problem of farming are farmers, the state as well as the as the Central Government has developed various plans like the Green Revolution.
• The concept developed by Dr. Swaminathan the new irrigation projects, the new seeds and fertilizers developed by various Agricultural Universities, market analysis of the agricultural produces. Drought Prone Area Development Programmes etc.
• With all these efforts, the Indian Farmer is not happy with the present uncertainties in farming activities.

Key Takeaways:

The agriculture is the base or culture and has provided a sound occupation to the people in the rural areas and provides the 'food' to all the Indians.

6.13 Calculation of Canal & Reservoir Capacities:

• The variable St is calculated via way of means of the subsequent equation: St = | St-1 + Rt - It | zero if bad or 0 if positive (1.2) The required garage potential is identical to the most of St values.
• Example 1.1: A reservoir is to be built at an area in which month-to-month float records are to be had for 28 months.

6.14 Duty & Delta:

• It is defined as, "it is the period to which the stated duty of water has reference." The total quantity of water is supplied to a crop, through a no. Of devices at central interval. The quantity of water to be given to a crop, during each watering. Varies and it is to be given a specific duration.
• So, the term "Duty of water" is used to indicate the quantity of water required to be given during each watering and it is referred to a specific period when the water is applied, so it is called as the base of the duty of water. When the duty of water is stated for each watering, its base also needs to be stated.
• The duty of water, expressed for each watering, also gives information about the actual rate at which is given to the crop on any day; or a number of days. But such information is not given, by the duty of water which is expressed
• For the entire base period of a crop, as it gives only the average rate of water application during that period. In fact, when the base is not mentioned, it is assumed that the duty of water refers to the entire base period.
• Delta (): "It is total depth of water required by a crop to came to maturity is called as Delta". It is measured in meters or centimeters.

Duty Hectares / Cumecs CD,

Delta A meters Base Period = 'B' day

One cumec of water flowing continuously for 'B' days; would give the depth of water 'A', over an area of 'D' hectares. The volume of water @ 1m3 sec in one day.

= 1x24x60x60 = 86400 m²

The volume of water @ 1 m³ sec 'B' days

= 1×24×60×60 = 86400 B m3

= 86400 m² m.    … (1)

As 1 hectare = 10,000 m², 1 m² = 1104 N

Then the equation becomes,

Volume of water @ 1 m³ sec in B days

= 86400 B m3

= 86400 B 1104 H-m volume of water @ 1 m³ sec in B days

= 864 x B H-m     …. (2)

The depth of water required by crop,

A = Volume of area A

= 8.64 x B H-m DHA

= 8.64 BDM (in F.P.S. System)

Let, Duty = D (Acres/cusecs)

Delta =A feat base period

= B days (by definition)

One cusec of water flowing continuously for B days, would give the depth of water 'A' over an area of 'D' acres.

The volume of water @ 1 ft3 sec. In one day

= 1x24 x 60 x 60 = 86400 ft3

The volume of water @ 1 ft2 sec for 'B' days

= 1×24×60×60 = 86400 B ft³

=86400 ft² ft

As 1 Acre = 43560 ft², 1 ft2=143560 Acres,

Then the equation becomes, volume of water @ lft3 sec, in 'B' days = 86400 ft3 = 86400 B × 143560 Acre-ft, volume of water @ 1 ft3 sec. In B days

= 1.983 B Acre-it      … (3)

The depth of water required by a crop.

'A' = Volume of Area 'A'

= 1.983 B Acre ft D Acre A = 1.983 x BD ft.

Key Takeaways:

It is defined as, "it is the period to which the stated duty of water has reference." The total quantity of water is supplied to a crop, through a no. Of devices at central interval. The quantity of water to be given to a crop, during each watering. Varies and it is to be given a specific duration.

6.15 Irrigation Efficiency:

• Irrigation efficiency (n.) is the optimum use of the water applied, for the growth of the plant. But it is fact that even with the best method of irrigation, there are always some losses through seepage, percolation and evaporation from the canals and also from the field.
• The ratio of, water available for use to the water applied can be defined as the efficiency of irrigation (Theoretically the ratio should be 1:1, to indicate optimum efficiency, but it never observed in reality.) Generally, the well irrigation has maximum efficiency as, the transit losses are almost nil as the well water is directly applied to the field (No chance of losses through seepage or percolation).
• Various methods are used to calculate various types of irrigation efficiencies which are expressed as below.

Water Conveyance Efficiency (nc)

• It is a ratio of the quantity of water delivered to the field (or to the irrigated land) to the quantity of water diverted into the canal system from the river or reservoir it is expressed in the following equation,

Where,

nc = water conveyance efficiency.

Wf = Quantity of water delivered to the field.

Wr= Quantity of water diverted into the canal system from the river or reservoir.

• So, this efficiency accounts for the losses of water, which occur in conveyance from the point of diversion into canal system to the field.

Water Application Efficiency (na)

• It can be defined as, "The ratio of quantity of water stored in the root zone of the plant, to the quantity of water delivered into the field". This ratio is expressed in the following equation.

Where,

= Water application efficiency.

Ws = The quantity of water stored in the root zone.

Wf = The quantity of water delivered into the field.

• So, this efficiency accounts for the losses of water, during the application of irrigation water to the field. The common losses during this process are from the surface runoff and from the deep percolation. So, if R, is the quantity of water lost due to surface runoff from the field and D, is the quantity of water lost due to deep percolation (which far below the root zone and so use less for the growth of plant).

∴

• This application efficiency varies as the methods of irrigation vary e.g. If the sprinklers are used for the irrigation of plants its efficiency is upto 80%, of the total quantity of water delivered to the field and in case of surface irrigation (canal or well) the efficiency never goes above 60% of the total quantity of water delivered to the field.

Water Use Efficiency (nu)

• It is the quantity of water used, beneficially, including the water required for leaching, to the quantity of water delivered. This ratio is expressed in the following equation.

Where,

= The water use efficiency,

Wu = The quantity of water used beneficially

Wf= The quantity of water delivered to the field.

Water Storage Efficiency (ns)

• It is the ratio of the quantity of water stored in the root zone (during the irrigation) to the total quantity of water needed to bring the moisture content of the soil to its field capacity. It is expressed in the following equation.

Where,

= Water storage efficiency.

Ws= Quantity of water stored in the root zone.

Wn = Quantity of water needed to bring the moisture content of the soil to the field capacity (Wn= field capacity available moisture in the soil, before irrigation).

Water Distribution Efficiency (nd):

• It is measure used to compare different methods of irrigation i.e., surface irrigation to sprinkler in irrigation methods. For that the following v equation is used:

Where,

= Water distribution efficiency.

y = The average numerical deviation in depth of water stored from the average depth of water.

d = The water stored in the root zone during irrigation.

• This efficiency evaluates, the degree, to which, the water is uniformly distributed throughout the root zone, during irrigation so, it is also called as "Uniformity coefficient".
• If the value of n, is higher, more will be the uniformity, which helps to get better crop response e.g. If n=80% means that, as compared to average depth of water application 10%, is the excess depth of water applied and 10% is the deficient depth of water applied.

Consumptive Use Efficiency (ncu)

• It is a ratio of normal consumptive use of water, to the net amount of water depleted from the root zone. The consumptive use efficiency can be calculated by using the following equation,

Where, = The consumptive use efficiency.

=We The normal consumptive use of water or evapotranspiration.

Wd = The net amount of water depleted from the root zone.

• So accounts for the loss of water by deep percolation any type of excessive evaporation, after the irrigation.

Key Takeaways:

Irrigation efficiency (n.) is the optimum use of the water applied, for the growth of the plant. But it is fact that even with the best method of irrigation, there are always some losses through seepage, percolation and evaporation from the canals and also from the field.

6.16 Piped Distribution Network for Irrigation (PDN): Introduction

• Pipe Distribution Network as an opportunity to standard open channel go with the drift irrigation device is the brand-new technique of irrigation wherein pipe community is laid rather than canal community with inside the command vicinity to deliver the water for irrigation.
• To deployation this device there are following recommendations to be followed - 

1. The intensity of PVC pipeline needs to be, 0.75m plus the dia. Of PVC pipe, from the floor, for the pipe diameters more or equals to 110mm.
2. Provide air launch valve at the best factor with inside the pipe community as indicated with inside the map.
3. Discharge on the chak head via pipe outlet is ruled through its diameter that's proportionate to the CCA of the chak. The designed dia. Of Main, Sub-main, and Lateral have to be strictly followed.
4. A drain valve has to be furnished anyplace pipeline crosses valley, nalla or river etc.
5. Valves have to be enclosed with RCC pipe having RCC cover. RCC pipe dia. Should be 1.0m for a Drain valve/Flow manage ball valve, and 0.6m for Air launch valves.
6. The pipe outlet needs to be 10 to 15cm. Above soil floor withinside the field.

6.17 Advantages & Disadvantages of PDN over conventional canal distribution network & its application:

Advantages of PDN:

• Following blessings are pretty probable because of properly planned, cautiously designed, nicely constructed, systematically operated and safely maintained PDN. Improved OPE

1. Less M & R problems (underground pipeline!)
2. Easy O & M (diploma of simultaneous irrigation being relatively more)
3. Saving in price of land acquisition
4. No want of fragmentation of fields
5. Benefit of percolation to wells withinside the command may, however, get decreased to a few extent

Disadvantages of PDN:

• Problems like much less availability of water withinside the reservoir, diversion of water from irrigation to non-irrigation or from glide to boost irrigation, encroachment of silt in stay storage, multiplied evaporation losses because of greater water use in HW, tendency of farmers to head for coins vegetation requiring greater water, unauthorized water use, deferred and / or loss of maintenance, vandalism & tampering of the machine, non-adherence to irrigation scheduling, loss of beneficiary- participation, etc. cannot be addressed most effective via PDN.
• PDN, therefore, ought to now no longer be visible and believed to be a panacea (treatment for all varieties of illnesses or troubles)! Success of PDN too will in the end rely upon stated macro stage problems.
• The effect of PDN and the significance of distinction it might make could be acknowledged most effective after critical intensive put up assignment assessment in due route of time.
• But it's miles really well worth attempting & attempting in a comprehensive & holistic way shall in reality make certain fulfillment of PDN Introducing PDN in current tasks is relatively hard because the machine constraints can also additionally create a few problems in scrupulously following the ideas of PDN.
• Combination of open-channel and PDN can also additionally call for unique preparations for water stage and discharge manage in discern open channel to make certain layout discharge in PDN. This is crucial due to the fact PDN in gravity machine is already designed for “low head”. If that “head” additionally receives similarly decreased or fluctuates significantly, then PDN might not supply favored results.

6.18 Assessment of Canal Revenue:

• To reduce the danger of unexpected variations in the S.W. Monsoon rainfall, the farmers are provided the irrigation water through the canals which fetch the water from the dammed reservoirs.
• The construction of dam and the main canals cost a huge amount to the government. So, it is necessary to collect this cost from the actual users of the canal water.
• For a better maintenance of the canal, regular expenses are required. So, it is necessary to get certain revenue from the farmers in the form of irrigation water charges.
• The need to collect the water charges is mainly to collect the funds to make these projects self-supporting and also to raise the funds to be used for some zero irrigation projects.
• Such irrigation water charges are justifiable because of the following reasons.
• A: The irrigation water supply not only makes agricultural activities safe (due to regular and controlled water supply) but also it helps to increase the yields, to get more profits to the farmers.
• B: The farmers can invest more amount for cultivation e.g., for better seeds, better fertilizers, better pesticides etc., as the danger of droughts has been put under control.
• C: When the rain fed agricultural land gets converted into irrigated land. The mark price of such land increase.
• So, the farmers always are ready to make the regular payments as the water charges to the government.

Key Takeaways:

To reduce the danger of unexpected variations in the S.W. Monsoon rainfall, the farmers are provided the irrigation water through the canals which fetch the water from the dammed reservoirs.

6.19 Various methods (Area basis or crop rate basis, Volumetric basis, Seasonal basis, Composite rate basis, Permanent basis or betterment levy basis):

Area or Crop Rate Basis:

• These rates are fixed per unit of land irrigated for each of the crop grown. These rates of water charges for different crops are based on the following factors.

1. The cash value of the crop (it indicates the paying capacity of the farmer).
2. The average water requirement of the crop.
3. Time of demand for water in relation to the available water in the river or reservoir e.g., in summer the storage of water is reduced while in winter due to less evaporation the storage is more.

Merits of area or Crop Rate basis Method:

1. The method is easy to be operated.
2. It is convenient to both the parties i.e., the supplies of water (government Irrigation department) and the actual user (the former).
3. It can be used for the lift-irrigation schemes.

Demerits of Area or Crop Rate basis Assessment Method

• As the water charges are not based on the actual water supplied but on the total land irrigated there is chance of wastage of water. i.e., the farmer does not try to have the economical use of the water.
• The cultivators near the head reaches of the canal make use of more water (than his share) and farmers who are near the tail end of the canal are deprived of their share of water. So, this creates uneven distribution irrigation water.
• The farmers make use of the irrigation water for a limited land (to be used for cash crop plantation) and make over use of water as they have to make payment on the basis of the area irrigated (and not the volume of water used.)

The Volumetric Assessment:

• In this method the water charges are fixed on the basis of total volume of water supplied to the farmer. To measure the actual water supplied the water meters are installed at the outlets of the canal.

Merits of Volumetric Assessment

1. As the farmer has to pay for the volume of water, he tries to make maximum use of water supplied to him, so this helps reduce the wastage of water.
2. It is an eco-friendly method to conserve the water resource.

Demerits of Volumetric Assessment

1. The initial cost of this system is very high as at each of the outlet the water meters are to be installed and they also need regular maintenance.
2. A full-time staff is to be appointed to keep the up-to-date record of the water-meters.
3. These water meters may not work on the small heads at the outlets.
4. The flow through meter may get obstructed due to saturation of silt, or debris.
5. The actual uses may make modification in the water meter illegally.
6. It is difficult to calculate the water supplied to each of the farmer in group who get water from one outlet only. (This problem is faced when the water is supplied a co-operative lift irrigation scheme, having the small holding of farmers.)

The Assessment on Seasonal Basis:

• In this, the water charges are fixed on the basis of the season and the type of crop grown. The value of the crop is not considered while fixing the water charges.
• These charges vary from season to season. e.g., The supply of water during summer per volume of water will be costlier than the same volume of water supplied during rainy season.
• This is not a popular method of assessment in our country.

The Assessment on Composite Rate Basis or the Consolidated Assessment:

• In this method the farmers have to pay an additional amount called as land revenue above the water charges. So, it is called as Composite or consolidated Assessment method.
• This also is not a popular method to assess the water charges.

The Permanent Assessment or The Betterment Levy:

• This method is used in the regions having the private water supply of the farmers (mainly having well-irrigation). These farmers make use of the canal water during the drought conditions when they dug wells water supply is stopped mainly during summers.
• In such cases a fixed levy is imposed on the farmers, which they have to pay every year. It is called as betterment levy.
• Those who pay such levy every year are allowed to make use of the canal water (mainly during drought) without making only extra payment for the irrigation water used by them. As they have to pay this betterment levy every year permanently, it is also known as, Permanent Assessment Method.

Numericals:

Q. A duty for a crop is 1152 hectares/cumec on the field, the base period of this crop is 120 days.

Soln.:

Duty D= 1152 hectares/cumec

Base period B=120 days

Delta=0.9m

Q. A crop required 1080 mm of water for a base period of 125 days. Find the duty of water.

Soln.:

Given:

Delta

Base period B=125 days

To find: Duty D=?

Duty D=

References:

1. A textbook of Hydrology, Dr. P. Jaya Rami Reddy, USP Publisher

2. Irrigation, Water Resources and Water Power Engineering, P.N. Modi.

3.Irrigation and Water Power Engineering, Dr. Purnima and Dr. Pande

4. Irrigation Engineering, Bharat Singh, Nem Chand & Bros. India

5.Irrigation Engineering, H.M Raghunath, Wiley