NABARD Grade-A Exam : Notes on Agriculture & Rural Development | Irrigation Management: Types of Irrigation, Sources of Irrigation, Crop Water Requirement.

NABARD Grade-A Exam : Notes on Agriculture & Rural Development (with focus on Rural India)

The upcoming important exams are NABARD grade A and grade B, in which there is a section Agriculture & Rural Development (with a focus on Rural India) having high weightage of 40 marks. So, for the same, it becomes really important to have an in-depth knowledge of the various terminologies and practices involved in agriculture. Further its imperative to be aware of the present scenario of Indian Agriculture and the state of Rural Development in India. To help you with this, today, we are providing you with all necessary information related to the mentioned field which will help you to fetch some good marks.

Irrigation
Irrigation is defined as “Artificially supplying & systematically dividing of water for agriculture & horticulture in order to obtain higher or qualitatively better production”. It is one of the most important critical inputs for enhancing the productivity that is required at different critical stages of plant growth of various crops for optimum production.

Irrigation Management
Management of water based on the soil and crop environment to obtain better yield by efficient use of water without any damage to the environment. Management of water, soil, plants, irrigation structure, irrigation reservoirs, environment, social setup and it’s inter liked relationship are studied in the irrigation management.
For this we have to study soil’s physical and chemical properties, biology of crop plants, quantity of water available, time of application of water, method of application of water, climatological or meteorological influence on irrigation and environment and & changes due to irrigation.
Management of all the above-said factors constitutes Irrigation Agronomy. Management of irrigation structures, conveyances, reservoirs constitutes Irrigation Engineering.

Importance of Irrigation
a) Uncertainty due to insufficient, uncertain and irregular rain causes:  The period of rain is restricted to only four months in a year, June to September, when monsoon arrives. The remaining eight months are dry. There is some rainfall during the months of December and January in some parts of the country. Even during monsoon, the rainfall is scanty and undependable in many parts of the country. Sometimes the monsoon delayed considerably while sometimes they cease prematurely. This pushes large areas of the country into drought conditions. With the help of irrigation, droughts and famines can be effectively controlled.
b) Higher productivity on irrigated land: Productivity on irrigated land is considerably more than the productivity on un-irrigated land.
c) Multiple cropping possible: Since India has a tropical and sub-tropical climate, it has potentialities to grow crops on a year-round basis. However, since 80% of the annual rainfall is received in less than four months, multiple cropping is generally not possible. Provision of irrigation facilities can make possible the growing of two or three crops in a year in most areas of the country.
d) Role in new agricultural strategy: The successful implementation of the High Yielding Programme enhances agricultural production to a great extent.
e) Bringing more land under cultivation: Cultivable wasteland comprises another 13.83 million hectares. Cultivation On all such lands is impossible in some cases while in others it requires substantial capital investment to make land fit for cultivation. Provision of irrigation facilities can make some portion of this land cultivable.
f) Reduces instability in output levels: Irrigation also plays a protective role during drought years. Irrigation has enabled many states to acquire ‘partial immunity’ from drought.
g) Indirect benefits of irrigation: Irrigation confers indirect benefits through increased agricultural production. Employment potential of irrigated lands, increased production, helps in developing allied activities, means of water transport etc. are improved income of government from agriculture. Availability of regular water supply will increase the income of farmers imparting a sense of security and stability in agriculture.

Irrigation systems are often designed to maximize efficiencies & minimize labor & capital requirements. There are three broad classes of irrigation system:
a) Pressurized distribution: The pressurized systems include sprinkler, trickle, in which water is conveyed to & distributed over the fields through pressurized pipe networks.
b) Gravity flow distribution: This system conveys & distributes water at the field level by a free surface, overland flow regime.
c) Drainage flow distribution: Irrigation by control of the drainage system sub-irrigation is not so common but is interesting. Relatively large volumes of applied irrigation water percolate through the root zone & become a drainage or groundwater flow. By controlling the flow at critical points, it is possible to raise the level of the groundwater to within reach of the crop roots.

To supply water the entire field uniformly so that each plant would get sufficient amount of water, there are various types of irrigation techniques that differ in how the water obtained from the source is distributed within the field. These are:
a) Surface Irrigation: In this irrigation system water moves over & across the land by simple gravity flow in order to wet it & to infiltrate into the soil. Surface irrigation can be subdivided into furrow, border strip or basin irrigation. It is often called flood irrigation when the irrigation results in flooding or near flooding of the cultivated land.
b) Ditch Irrigation: This is the simplest & oldest irrigation system & it is still common in many parts of the world. The only technology essential is the manpower or machines to dig ditches or furrows between the rows of plants. Water is added to the ditches by means of gravity flow, pumps & siphons.
c) Localized Irrigation: It is a system where water is distributed under low pressure through a piped network, in a predetermined pattern, & applied as a small discharge.
d) Drip Irrigation: This is also known as trickle irrigation. Water is delivered at or near the root zone of plants; drop by drop. This method can be the most water-efficient method of irrigation.
e) Overhead Irrigation: This is the artificial application of water to crops from above. Central pivot systems, which are in wide use in areas of flat terrain, have sprinklers spaced along very long aluminum or steel pipes that extend in two directions from a central supply point. Sprinkler systems are another very common overhead irrigation system. In these systems, water is piped to a point within the area to be irrigated.
f) Sub-Irrigation: This is also called as seepage irrigation used for many years in the fields where water table is high. This method artificially raises the water table by allowing the soil to be moistened from below the plant's root zone.
g) Manual Irrigation: This system has low requirements for infrastructure & technical equipment but needs high labor inputs by using buckets or watering cans.

According to the different sources of irrigation, there are two major divisions found. These are:
a) Flow Irrigation: The water of a reservoir or tank usually remains at a higher level & when a channel is connected to it, water automatically flows down the channel which fulfills the purpose of a canal for irrigation. In this case, water level remains higher than the fields. Such irrigation is known as the flow irrigation.
b) Lift Irrigation: Where the fields lie at a higher level & the canals or tanks lie at a lower level, it becomes essential to lift the water by pump etc. to irrigate land. Water is lifted from tanks, wells & tube wells by pumps for irrigation through channels. This method of irrigation is known as the lift irrigation.

Limitations of Irrigation:
Despite large-scale investment and expansion of irrigation facilities, it is a matter of serious concern that about 60 percent of the total cropped area is still dependent on rain. There are a number of problems related to irrigation and they have to be solved.
a) Delays in completion of projects
b) Inter-state water disputes
c) Regional disparities in irrigation development
d) Waterlogging and salinity
e) Increasing cost of irrigation
f) Losses in operating irrigation projects
g) Decline in water table

Sources of Irrigation
Depending upon the availability of surface or groundwater, topogra­phy, soil, rainfall conditions and rivers, various types of irrigation are practiced in India.

Canal Irrigation:
A canal is an artificial watercourse constructed for water supply and irrigation. Canals can be an effective source of irrigation in areas of low relief, deep fertile soils, perennial source of water and an extensive command area. Therefore the main concentration of canal irrigation is in the northern plains. The canals are practically absent from the peninsular plateau region because of rocky terrain. However, the coastal and the delta regions in South India have some canals for irrigation.
There are two types of canals:
Inundation Canals – These are taken out from the rivers without any regulating system like weirs etc at their head. Such canals are useful only during the rainy season
Perennial Canals – These are those which are taken off from perennial rivers by constructing a barrage across the river. Most of the canals at present in India are perennial.

Merits: Perennial Source; Provides safety from droughts; Brings fertile sediments to the fields; Economical to serve a large area
Demerits: Canal water soaks into the ground and leads to waterlogging, increases salinization, and leads to marshy conditions leading to malaria and flooding; Wastage of water.

Wells (and Tube Wells)
This method of irrigation has been used in India from time immemorial. Various methods are used to lift the groundwater from the well. Some of the widely used methods are the persian wheel, reht, charas or mot, and dhinghly (lever) etc. Well, irrigation is gradually giving way to energized tube wells. It is particularly suitable in areas with permeable rock structure which allows accumulation of groundwater through percolation. Therefore wells are seen more in areas with alluvial soil, regur soil, etc. and less seen in rocky terrain or mountainous regions.

Merits: Simplest and cheapest; Well is an independent source of irrigation and can be used as and when the necessity arises. Canal irrigation, on the other hand, is controlled by other agencies and cannot be used at will; Some groundwater salts are useful for crops ;Does not lead to salinization and flooding problems; There is a limit to the extent of canal irrigation beyond the tail end of the canal while a well can be dug at any convenient place.
Demerits: Only limited area can be irrigated; Not suitable for dry regions; Overuse may lead to lowering of water table.

Tank irrigation
A tank is a reservoir for irrigation, a small lake or pool made by damming the valley of a stream to retain the monsoon rain for later use. It is practiced mainly in the peninsular region due to the following reasons: 
a) Undulating relief and hard rocks make it difficult to dig canals and well
b) Little percolation of water due to hard rock structure and groundwater is not available in large quantities
c) Most of the rivers are seasonal; there are many streams which become torrential during the rainy season – so the only way to use this water is to impound it by constructing bunds and building tanks.  Also, it is easy to collect rainwater in natural or artificial pits because of impermeable rocks.
d) Scattered nature of agricultural fields

Merits: Most of the tanks are natural and do not involve cost for their construction; Independent source for an individual farmer or a small group of farmers; longer lifespan; can be used for fishing also
Demerits: Depends on rain and these tanks may dry up during the dry season; Silting of their beds; Require large areas; Evaporation losses; Sometimes there might be a need to lift the water to take it to the field

Crop Water Requirement
Crop water requirement is the water required by the plants for its survival, growth, development and to produce economic parts. This requirement is applied either naturally by precipitation or artificially by irrigation. Hence the crop water requirement includes all losses like:
a) Transpiration loss through leaves (T)
b) Evaporation loss through soil surface in cropped area (E)
c) Amount of weather used by plants (WP) for its metabolic activities which is estimated as less than 1% of the total water absorption. These three components cannot be separated so easily. Hence the ET loss is taken as crop water use or crop water consumptive use.
d) Other application losses are conveyance loss, percolation loss, runoff loss, etc., (WL).
e) The water required for special purposes (WSP) like puddling operation, ploughing operation, land preparation, leaching, requirement, for the purpose of weeding, for dissolving fertilizer and chemical, etc.

The following features which mainly influence the crop water requirement are:
a) Crop factors: Variety; Growth stages; Duration; Plant population; Crop growing season
b) Soil factors: Structure; Texture; Depth; Topography; Soil chemical composition
c) Climatic factors: Temperature; Sunshine hours; Relative humidity; Wind velocity; Rainfall
d) Agronomic management factors: Irrigation methods used; Frequency of irrigation and its efficiency; Tillage and other cultural operations like weeding, mulching etc / intercropping

Crops
Duration(Days)
Water Requirement(mm)
Notes
1. Rice
135
1250
The growth of rice plant in relation to water management can be divided into four periods viz. Seedling, vegetative, reproductive and ripening. Less water is consumed during seedling stage.
2. Groundnut
105
550
Evapotranspiration is low during the first 35 days after sowing and last 35 days before harvest and reaches a peak requirement between peg penetration and pod development stages.
3. Sorghum
100
350
Irrigation prior to heading and ten days after heading are essential for successful crop production.
4. Maize
110
500
Uniformly requires water in all stages
5. Sugarcane
365
2000
The response for applied water is more during this critical phase during which the crop needs higher quantity of water comparing, the other two phases.
6. Ragi
100
350
a drought tolerant crop.
7. Cotton
165
550
Little water is used by plant with early part of the season and more water is lost through evaporation than transpiration.
8. Pulses
65
350
Mostly are grown under rainfed condition.