Here is a compilation of essays on ‘Irrigation’ for class 7, 8 ,9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Irrigation’ especially written for school and college students.
Essay on Irrigation
Essay Contents:
- Essay on the Introduction on Irrigation
- Essay on the Irrigation Sector Terminology
- Essay on the Irrigation and Water Resources in India: Competition for Scarce Resources
- Essay on the State of Irrigation in India
- Essay on the Benefits of Irrigation
- Essay on the Water Management for Irrigation
- Essay on the Methods of Irrigation
- Essay on the Drip and Sprinkler Irrigation in India: Constraints
- Essay on the Adverse Effect of Improper Irrigation
- Essay on the Crop Water Requirement
- Essay on the Delta of Crop
Essay # 1. Introduction on Irrigation:
Irrigation is the artificial application of water for the cultivation of crops, trees, grasses and so on. For the urban Indian, the word ‘irrigation’ conjures up images of the first Prime Minister of India, Jawaharlal Nehru, and the Bhakra Nangal Dam (Temples of Modern India) and images of Medha Patkar, Aamir Khan, and the tribal oustees of the Narmada dam. These are diverse perspectives on the story of large irrigation infrastructure in India. In fact, in popular public perception, irrigation connotes ‘large irrigation infrastructure’ rather than provision of irrigation services.
For a typical Indian farmer, looking up to the skies to see whether the rain gods will favour him this time, irrigation means a wide range of interventions at the farm level, ranging from a couple of support watering(s) (or ‘life saving’ watering) during the kharif (monsoon) season from a small check dam/ pond/tank/dry well to assured year-round water supply from canals or tube wells to farmers cultivating three crops a year. The method of application has also evolved, from traditional gravity flow and farm flooding to micro-irrigation where water is applied close to the root zone of the plant.
Indian farmers gain access to irrigation from two sources-surface water (that is, water from surface flows or water storage reservoirs) and groundwater (that is, water extracted by pumps from the groundwater aquifers through wells, tube wells and so on). Surface irrigation is largely provided through large and small dams and canal networks, run-off from river lift irrigation schemes and small tanks and ponds.
Canal networks are largely gravity-fed while lift irrigation schemes require electrical power. Groundwater irrigation is accessed by dug wells, bore wells, tube wells and is powered by electric pumps or diesel engines. To meet the growing needs of irrigation, the government and farmers have largely focused on a supply side approach rather than improve the efficiency of existing irrigation systems.
Essay # 2. Irrigation Sector Terminology:
The terms used by the Ministry of Water Resources (MoWR), Ministry of Rural Development (MoRD), and the Ministry of Agriculture (MoA), the three ministries within the government responsible for irrigation are as follows:
1. Major irrigation (cultivable command area above 10,000 ha).
2. Medium irrigation (cultivable command area between 2000 ha to 10,000 ha).
3. Minor irrigation (cultivable command area less than 2000 ha).
(a) Surface irrigation.
(b) Groundwater irrigation.
This classification belongs to an era when all ‘irrigation’ was largely surface irrigation, promoted and supported by the government. Hence, groundwater irrigation, which was in its infancy till the 1960s, is slotted into minor irrigation as each ‘scheme’ (or well/bore well) in its individual capacity irrigates 1 to 5 ha of land. Minor irrigation also includes a large number of small surface irrigation schemes such as village tanks, and ponds, including many which were constructed pre-independence and managed by the local community and have been now handed over to the panchayat administration.
Two other terms which are critical to our understanding of irrigation sector are ‘watershed’ and ‘micro-irrigation’. ‘Watershed’ may be defined as an area from where rainwater is drained through a common outlet (lake/river/rivulet) and therefore, can range in size from a few states to a few ha. It is a hydrologic unit which is useful for natural resource planning and management.
The watershed programme, funded by the Ministry of Rural Development (MoRD) and Ministry of Agriculture (MoA), focuses on a range of multi-disciplinary interventions (afforestation, soil and water conservation measures, water harvesting and so on) in a watershed which is demarcated so as to be as contiguous to the village boundary as possible.
The watershed programme is a key programme of the MoRD and MoA to increase agriculture productivity in areas which are rainfed and cannot access any surface irrigation scheme (the watershed programme guidelines specifically prohibit work on villages which have more than 30 per cent area already under irrigation).
Micro-irrigation encompasses drip and sprinkler technologies. Traditionally, irrigation is provided to crops by flooding the entire farm, largely through gravity- based flow. To get ‘more crop per drop’ two major technologies of drip and sprinkler irrigation have been developed. In both these technologies, water is available in quantities and location more suitable to the plant growth and near the root zone. Use of these technologies improves the efficiency of irrigation. Application of micro-irrigation devices leads to 30-70 per cent water savings relative to flood irrigation.
Essay # 3. Irrigation and Water Resources in India: Competition for Scarce Resources:
The world over, the irrigation sector is the largest user of water-almost 80 per cent of the water in the world is taken up by irrigation (in India, the irrigation sector uses -85 per cent of its available water resources). The average rainfall in India is 1170 mm and given the geographical area of 3.3 million km, gives India 4000 cu km of water.
Almost 50 per cent of this water is lost to evaporation, percolation, sub-surface flows to oceans and only 1953 bcm is accounted for. Because of spatial and temporal variation in the availability of water, only 1086 bcm is utilizable (Phansalker and Verma, 2005). An availability of 1700 cubic meters of water per capita annual water resource (AWR) is safe (Falkenmark et al. 1976). India’s AWR was 2214 cum in 1996 but is estimated to go down to 1496 cum by 2025.
Also, while the AWR is high now, the real availability of water is based on the developed water resource (DWR) which is only 25 per cent of the AWR (Gulati et al. 2005). Also, the national averages do not tell the whole story as water is a local issue and there are many regions in India where water availability per capita is below the safe level. The other main users of water, (urban and rural drinking water), industry and environment, show an increase in demand.
As urbanization increases in India, demand for water from the urban sector will increase. Already water conflicts are rising with irrigation water being diverted for urban drinking water supplies in times of scarcity. Farmers in Rajasthan have not allowed dam waters to be drained to the Bharatpur Sanctuary. With an increasing population and growing needs, the gap between the demand and availability will only widen with time.
Hence, irrigation as a sector will be under increasing pressure from other sectors to share scarce water. The irrigation sector will be compelled to introduce reform towards better water management and minimization of wastage to be able to meet its growing demands from progressively less water availability per capita.
Essay # 4. State of Irrigation in India:
In India, the irrigated area is 34 per cent of the net area sown. The gross irrigated area is 80 million ha which gets India the prize for the largest amount of irrigated agriculture in the world. The break-up is given in Table 2.12.
The so termed ‘minor’ irrigation is now the major source as groundwater provides 50 per cent of the gross area under irrigation (in fact recent data shows that in terms of net sown area, groundwater provides 60 per cent of the net irrigated area (Shah and Deb, 2004). As can be seen, the potential created so far (till 1997) is only 64 per cent of the UIP.
Thus, groundwater is a critical element in filling the need gap for the rural farmers, as it has provided irrigation in areas where the public irrigation systems have not reached or where the service delivery has been poor. In the last two decades, 84 per cent of the addition to net irrigated area has come from groundwater.
The Ultimate Irrigation Potential (UIP) is an estimate prepared by the Ministry of Water Resources of the overall potential for irrigation in the country.
1. Major and Medium Irrigation:
In terms of investment by the government, major and medium irrigation sector accounts for 57 per cent of investment in the irrigation sector which serves only 35 per cent of the total area irrigated. The infrastructure is ageing; there is an increased siltation of large dams, time and cost over-runs, and tail-ender deprivation.
Ageing of the Infrastructure:
Almost 60 per cent of the total irrigation of the country are more than two decades old (Figure 2.38). Canal networks also need annual maintenance. Besides regular maintenance, many older structures need replenishment for which funds are a constraint.
Increased Siltation of Large Dams:
The Inter-Ministry Task Force on large reservoirs maintains that one third of their storage capacity has been affected by siltation, resulting in reduced area under irrigation and lowering the life of the dam. In most cases the rate of siltation is far in excess of the rate assumed during construction (Planning Commission, 2002).
Time and Cost Over-Runs:
Another issue related to most large dams is that they are not completed within the scheduled period or budget and spill over from one 5 year plan to another. When the Tenth Plan began, there were 410 on-going projects, some of them started in the Fifth Five-Year Plan. The spillover costs from previous projects to the Tenth Plan are Rs. 17,700 crore which is more than the allocated amount (MoRD, 2006). These delays have not only led to escalated costs but also to delays in returns from the investment and lower the viability of these projects.
Tail-Ender Deprivation:
Farmers who have land at the end of the canal system are called tail-enders. They include farmers in the tail reach as well as those at the end of the upper and middle reaches of the canal system. It has been known that many get neither enough nor timely water. A national research study undertaken by the Development Support Centre shows that tail-ender deprivation is far more than assumed thus far.
In Gujarat, in a major water deficient project Dharoi with 45,000 ha of command area, the tail-enders’ problem was found in 37 per cent of the command area. Even in the areas with warabandi system in Punjab and Haryana, 70 per cent of the tail-end farmers got 54 per cent to 70 per cent less water than they were entitled to.
A good example of how this is hidden from the existing monitoring system is the large Tungabhadra system in Karnataka where farmers in the last reach got 91 per cent less water than they were entitled to even though the project performance was claimed as 90 per cent (DSC, 2003). A major impact of this was the lower agricultural productivity of tail-end farmers, movement to low-value crops or practice of leaving land fallow.
The causes of tail-ender deprivation are excessive use by head-reach farmers, poor maintenance, less funds allotted to tail regions for maintenance, poor construction, and design fault.
2. Minor Irrigation:
Minor irrigation, currently covers 52.62 million ha of land. The third minor irrigation census carried out in 2000-1 covered 6.3 lakh villages in 586 districts. It showed 19.7 million ha of irrigation of which 18.5 million are groundwater schemes and 1.2 million are surface water irrigation.
The 18.5 million groundwater schemes have created an irrigation potential of 62.4 million ha (3.37 ha per schemes) while the 1.2 million surface irrigation schemes have created an irrigation potential of 11.9 million ha (9.9 ha per scheme). The surface and groundwater schemes are very different in nature and we analyse concerns and potential later.
Surface Water Schemes in Minor Irrigation:
The average command area of the surface water schemes is about 10 ha (Census, 2001). This adequately covers the range of schemes included in this category from small ponds with a command area of 2 to 5 ha to large flow irrigation systems with a capacity of 5200 ha and more. Administratively, in most states minor irrigation schemes are managed by the Panchayat irrigation department.
Since there are a large number of schemes with low command area and are dispersed over many villages, existing panchayat irrigation staff for managing these schemes is much less. In most cases, village panchayats do not have the resources to maintain these schemes on their own leading to shrinkage in use of this potential to only 58 per cent i.e. 6.9 million ha only.
The major structures under surface irrigation schemes are tanks and water harvesting structures which amount to 0.55 million structures out of the 1.2 million schemes. In drought prone areas where rainfall is uncertain, like Rajasthan, the tanks have fallen into disuse. Out of the 0.55 million tanks only 0.47 million tanks are in use. About 3 million ha potential irrigation is lost because of non-use or under-utilization of these tanks.
The major issues concerning minor irrigation are:
a. Lack of attention by the irrigation institutions;
b. Siltation and non-availability of power;
c. Though technically they belong to the panchayat, they are neither managed by them nor are the funds routed through them. Hence, the community ownership of many of these panchayats is very low;
d. Traditional institutions-community-based organizations (CBO) which used to – manage these tanks, do not exist now and new institutions at the village level to address the changing needs of the villagers have not yet evolved.
3. Groundwater Irrigation:
Groundwater now contributes to 60 per cent of the area irrigated in India. India also has the highest annual groundwater extraction in the world. Since 1970, it has been contributing more to agricultural wealth than surface irrigation. The contribution of groundwater increased from Rs. 22 billion in 1970 to 132 billion in 1993 while surface water increased from 77 billion to 115 billion (Shah and Deb, 2004).
Tube wells are now the largest source of irrigation in the country and their share has increased from 1 per cent in 1960-1 to 37 per cent in 1999-2000 (MoRD, 2006). Since this sector has almost no dependence on the government, it is growing at a rapid rate and it is estimated that one million wells are added every year (Shah and Deb, 2004).
Being an individually managed source, ground water irrigation is also a more efficient form of irrigation, with crop yields per cubic meter of water being 1.2 to 3 times higher than surface irrigation. However, since this sector has grown through investment by individual farmers, with little state involvement compared to canal irrigation, government support for understanding this sector and improving its performance is negligible.
The major issues for the future growth of groundwater irrigation are
a. Declining resource base,
b. Demand driven growth, and
c. A lack of policy and regulatory framework.
a. Declining Resource Base:
While on the average out of the 430 bcm available, only 160 bcm is withdrawn, this average hides the localized stress on the resource of large regions currently dependent on groundwater. The number of blocks which have more than 90 per cent groundwater development (GWD) is increasing. In Punjab, Haryana, and Rajasthan more than 40 per cent of the blocks are over-exploited and for the country as a whole, 14 per cent of the blocks are over-exploited. This is expected to increase to 60 per cent in the next 25 years.
b. Demand Driven Growth:
There are many regions of India with hard rock geology which have lower groundwater potential than the alluvial plains. Since groundwater extraction is primarily driven by the needs of the population and the density of farmer population and not the quality of resource, groundwater irrigation is scaling up even in such hard rock areas causing irreversible depletion of their source base.
c. Policy Vacuum:
Currently there is no policy framework governing the use of groundwater. In 1974, the central government had introduced the Groundwater Act which was not adopted by any state. In any case, most policy makers feel that regulating thousands of wells is operationally not possible.
However, the first requirement for evolving effective policies is to shift from water resource development to water resource management as in many areas, development has already taken place and if not managed, will lead to collapse of the groundwater resource. Options which can be considered are a combination of legal measures with indirect regulation through power supply.
Essay # 5. Benefits of Irrigation:
With the introduction of irrigation, there have been many advantages, as compared to the total dependence on rainfall.
These may be enumerated as under:
1. Increase in Crop Yield:
The production of almost all types of crops can be increased by providing the right amount of later at the right time, depending on its shape of growth. Such a controlled supply of water is possible only through irrigation.
2. Protection from Famine:
The availability of irrigation facilities in any region ensures protection against failure of crops or famine due to drought. In regions without irrigation, farmers have to depend only on rains for growing crops and since the rains may not provide enough rainfall required for crop growing every year, the farmers are always faced with a risk.
3. Cultivation of Superior Crops:
With assured supply of water for irrigation, farmers may think of cultivating superior variety of crops or even other crops which yield high return. Production of these crops in rain-fed areas is not possible because even with the slight unavailability of timely water, these crops would die and all the money invested would be wasted.
4. Elimination of Mixed Cropping:
In rain-fed areas, farmers have a tendency to cultivate more than one type of crop in the same field such that even if one dies without the required amount of water, at least he would get the yield of the other. However, this reduces the overall production of the field. With assured water by irrigation, the farmer would go for only a single variety of crop in one field at anytime, which would increase the yield.
5. Economic Development:
With assured irrigation, the farmers get higher returns by way of crop production throughout the year, the government in turn, benefits from the tax collected from the farmers in base of the irrigation facilities extended.
6. Hydro Power Generation:
Usually, in canal system of irrigation, there are drops or differences in elevation of canal bed level at certain places. Although the drop may not be very high, this difference in elevation can be used successfully to generate electricity. Such small hydro electric generation projects, using bulb-turbines have been established in many canals, like Ganga canal, Sarada canal, Yamuna canal etc.
7. Domestic and Industrial Water Supply:
Some water from the irrigation canals may be utilized for domestic and industrial water supply for nearby areas. Compared to the irrigation water need, the water requirement for domestic and industrial uses is rather small and does not affect the total flow much. For example, the town of Siliguri in the Darjeeling district of West Bengal, supplies its residents with the water from Teesta Mahananda link canal.
Essay # 6. Water Management for Irrigation:
Of the two resources -land and water, management of the former is largely in the domain of agricultural engineers.
Management of water, on the other hand, is mostly the purview of the water resources engineer who has to decide the following:
i. How much water is available at a point of a surface water source, like a river (based on hydrological studies).
ii. How much ground water is available for utilization in irrigation system without adversely lowering the ground water table?
iii. For the surface water source, is there a need for construction of a reservoir for storing the monsoon runoff to be used in the lean seasons?
iv. What kind of diversion system can be constructed across the river for diverting part of the river flow into a system of canal network for irrigating the fields?
v. How efficient a canal network system may be designed such that there is minimum loss of water and maximum agricultural production?
vi. How can excess water of an irrigated agricultural fields be removed which would otherwise cause water logging of the fields?
In order to find proper solution to these and other related issues, the water resources engineer should be aware of a number of components essential for proper management of water in an irrigation system.
These are:
1. Watershed Development:
Since the water flowing into a river is from a watershed, it is essential that the movement of water over ground has to be delayed. This would ensure that the rain water falling within the catchment recharges the ground water, which in turn replenishes the water inflow to the reservoir even during the lean season. Small check dams constructed across small streams within the catchment can help to delay the surface water movement in the watershed and recharge the ground water.
Measures for the water shed development also includes aforestation within the catchment area which is helpful Li preventing the valuable top-soil from getting eroded and thus is helpful also in preventing siltation of reservoirs. Other soil conservation methods like regrassing and grass land cultivation process, galley plugging, nullah bunding, contour bunding etc. also come under watershed development.
2. Water Management:
Surface water reservoirs are common in irrigation systems and these are designed and operated to cater to crop water requirement throughout the year.
It is essential, therefore, to check loss of water in reservoir due to:
i. Evaporation from the water surface.
ii. Seepage from the base.
iii. Reduction of storage capacity due to sedimentation.
3. Water Management in Conveyance System:
In India the water loss due to evaporation, seepage and mismanagement in the conveyance channels (for canals and its distributaries) is exceptionally high-nearly 60%. Some countries like Israel have reduced this loss tremendously by taking several measures like lining of water courses, lining not only reduces seepage, but also minimizes weed infestation and reduces overall maintenance cost though the initial cost of providing lining could be high depending on the material selected.
4. On Farm Water Management:
Though this work essentially is tackled by agricultural engineers, the water resources engineers must also be aware of the problem so that a proper integrated management strategy for conveyance- delivery-distribution of irrigation water is achieved. It has been observed from field that the water delivered from the canal system to the agricultural fields are utilized better in the head reaches and by the time it reaches the tail end, its quantity reduces.
Often, there are land holding belonging to different farmers along the route of the water course and there is a tendency of excess withdrawal by the farmers at the upper reaches. In order to tackle this kind of mismanagement a proper water distribution roster has to be implemented with the help of farmers’ cooperatives or water user’s associations. At times farmers are of the opinion that more the water applied more would be the crop production which is generally not true beyond a certain optimum water application rate. Education of farmers in this regard would also ensure better on-farm water management.
5. Choice of Irrigation Method:
Though irrigation has been practiced in India from about the time of the Harappa civilization, scientific irrigation based on time variant crop water need within the constraints of water and land availability is rather recent. It is important to select the right kind of irrigation method to suit the particular crop and soil.
For example, following is a short list of available methods corresponding to the kind of crop:
Essay # 7. Methods of Irrigation:
Water is an important constituent of the plant body. Plants need water to carry on different physiological processes essential to their growth and development. A great deal of water from plant body is wasted through the process of transpiration. Therefore, to compensate this loss of water, absorption of water from soil is an important phenomenon. Soil gets water mainly from two sources viz. precipitation and irrigation.
Hence, irrigation is a process, other than natural precipitation, which supplies water to crops, orchards, grass, or any other cultivated, plants. In the wetter parts of the world where rainfed cultivation is practiced, the farmer’s activities consist of selecting suitable land, preparing the soil for cultivation; sowing, tending and harvesting the crops. Natural rainfall provides the water needed. But in many other places otherwise favourable for cultivation, natural rainfall does not provide all the water needed and, as such, irrigation of crops is required to make up this deficiency.
Techniques adopted -for carrying water from its source to the crop are called methods or modes of application.
These are:
i. Flooding- wetting all the land surface;
ii. Furrows- wetting only certain part of ground level;
iii. Sprinkler- in which the soil is wetted in much the same way as rains;
iv. Sub-surface irrigation- in which surface is wetted very lightly, but the sub soil is fully saturated; and
v. Localized irrigation- in which water is applied at each individual plant at a near daily rate.
Characteristics of an Efficient Irrigation Method:
An efficient method of irrigation should fulfill five major objectives viz.:
i. Distribution of water uniformly over the field according to crop need,
ii. Storage of maximum fraction of water in the root zone for plant use,
iii. Crop growth should not be adversely affected,
iv. Soil transport or loss is negligible, and
v. The technique used is economically sound and adoptable at the farm.
Factors Affecting Suitability of Irrigation Method:
The selection of a suitable irrigation method for a particular farm location depends upon the following factors:
1. Soil:
Textural, crusting, cracking and infiltration characteristics of surface soil; nature and depth of relatively impermeable layers in sub-soil, if any; water storage capacity of root zone; nature and extent of land slope; size of field; surface drainage; nature and extent of salts in surface and sub-soil are the salient soil factors influencing between of an irrigation method.
2. Water:
Nature of water supply (continuous or rational), source (pump or canal), size of water delivery, quality of irrigation water, and quantity of water supply (adequate or limited) area few factors that must be taken into consideration while deciding the method of irrigation.
3. Crops:
Nature of crops, area under different crops and their rooting behaviour, optimum depth and timing of irrigation, sensitivity of crops to excessive soil moisture, cultural operations required, etc. must be considered at the time of selection of irrigation method for a crop.
4. Others:
There are other factors influencing irrigation method like outlook, managerial efficiency and financial resources of the farmer; nature of the farm machinery used; availability and cost of labour; wear and tear maintenance facilities and costs of irrigation equipment; and availability of power supply.
As far as possible, an irrigation method should not only provide a high level of water application efficiency, but also ensure its economic viability, sustained soil productivity and wide’ adaptability to prevalent feature of the farm. Generally, irrigation methods followed in India lack in an economic use of irrigation water.
Essay # 8. Drip and Sprinkler Irrigation in India: Constraints:
India ranks first in respect of total irrigated area existing in the world. It has got approximately 80 million hectares of irrigated land. But the methods of irrigations employed are still very primitive and inefficient. Recent achievements in the field of irrigation for instance drip and sprinkler irrigations are yet not sufficiently popular in India.
More than 10 million hectare is irrigated by sprinkler method and I million hectare by drip irrigation in the world. But in India, it is only about 0.7 m. ha under sprinkler irrigation and less than 20,000 ha with drip irrigation. Therefore, it is necessary to popularize these advanced methods of irrigation especially in those areas where water is a scarce resource.
India is blessed with abundant water resources. However, the available water, particularly for irrigation is tending to diminish and at the same time its demand is gravely felt due to population explosion. The emerging challenge is to tap all the available resources of water.
Technological innovations are to be exploited to achieve the twin objectives of higher productivity and better water use efficiency. For this, we will have to popularize drip and sprinkler irrigation methods. On account of certain financial, technical and institutional constraints, these methods have not got their due place in India and consequently, the area benefited is negligible. Therefore, the question arises as to what are the constraints and problems holding up progress.
The following are the major constraints faced by the farmers in adopting the drip and sprinkler systems of irrigation:
i. High initial cost.
ii. Inadequate subsidy amount.
iii. Difficulty in getting subsidy amount.
iv. Lack of availability of technical input and after sale services.
v. Clogging of dripper and cracking of laterals.
vi. Damages due to rats and squirrels.
vii. High cost of spares and components.
viii. Discrimination in subsidy distribution among different categories of farmers.
To exploit the full potential of these two innovations, the constraints are to be overcome by appropriate policy instruments. Financial support and technical guidance. This calls for an integrated approach and endeavor on the part of government. Implementing agencies, manufacturing companies, voluntary organizations and the ultimate users of the systems i.e. the farmers.
Essay # 9. Adverse Effect of Improper Irrigation:
As water is a limited resource with no substitute, its efficient and judicious utilization is of utmost importance in sustaining and increasing agricultural production. If irrigational water is used inefficiently and unscientifically, it may cause certain adverse effects, rather than being useful, to the crop and soil.
Seepage from main and branch canals, distributaries, and field channels along with the deep drainage loss from the base and cropped fields due to heavy rains and over irrigation add to the ground water and cause rise of water table. If not checked, the water table may rise close to the surface and cause water logging of soil. If here is a salty layer in the soil, the salts may get dissolved in the rising water table and come up on the surface soil thereby rendering the soil less productive due to salinity. Soil aeration is also badly affected.
Rising of water table beyond the threshold depth can be prevented by providing requisite sub-surface drainage. Alternatively, in areas with good quality ground water, radial drainage with shallow pumps and recycling the water for irrigation can be practiced with advantage to keep down the water tables and stretch the irrigation supplies.
Another aspect associated with injudicious irrigation is leaching of the mobile nutrients like nitrate below the root zone of crops, which decreases the nutrient use efficiency by crops. In order to minimize this loss through leaching, it becomes necessary to regulate irrigation and fertilizer applications.
Essay # 10. Crop Water Requirement:
It is essential to know the water requirement of a crop which is the total quantity of water required from its sowing time up to harvest. Naturally different crops may have different water requirements at different places of the same country, depending upon the climate, type of soil, method of cultivation, effective rain etc.
The total water required for crop growth is not uniformly distributed over its entire life span which is also called crop period. Actually, the watering stops same time before harvest and the time duration from the first irrigation during sowing up to the last before harvest is called base period. Though crop period is slightly more than the base period, they do not differ from practical purposes. Figure 2.40 indicates the relative usage of water for a typical crop during its entire growth period.
Sometimes, in the initial stages before the crop is sown, the land is very dry. In such cases, the soil is moistened with water as helps in sowing the crops. This is known as paleo irrigation. A term kor watering is used to describe the watering given to a crop when the plants are still young. It is usually the maximum single watering required, and other waterings are done at usual intervals.
Essay # 11. Delta of Crop:
The total depth of water required to raise a crop over a unit area of land is usually called delta.
Some typical values of delta for common crops in some regions of India are as follows:
1. Rice:
i. 1000 mm to 1500mm for heavy soils or high water table.
ii. 1500 mm to 2000mm for medium soils.
iii. 2000 to 2500 for light soils or deep water table.
iv. 1600 mm for upland conditions.
2. Wheat:
i. 250 mm to 400mm in northern India.
ii. 500 mm to 600mm in Central India.
3. Maize:
i. 100 mm during rainy season.
ii. 500 mm during winter season.
iii. 900 mm during summer season.
iv. Cotton: 400 – 500 mm.
4. Sugarcane:
i. 1400 mm to 1500 mm in Bihar.
ii. 1600 mm to 1700 mm in Andhra Pradesh.
iii. 1700 mm to 1800 mm in Punjab.
iv. 2200mm to 2400mm in Madhya Pradesh.
v. 2800 mm to 3000 mm in Maharashtra.
Duty of Water:
The term duty means the area of land that can be irrigated with unit volume of irrigation water. Quantitatively, duty is defined as the area of land expressed in hectares that can be irrigated with unit discharge, that is, 1 cumec flowing throughout the base period, expressed in days.
Imagine a field growing a single crop having a base period B days and a Delta Δ mm. which is being supplied by a source located at the head (uppermost point) of the field, as shown in Figures 2.41 and 2.42.
The water being supplied may be through the diversion of river water through a canal, or it could be using ground water by pumping (Fig. 2.43).
If the water supplied is just enough to raise the crop within D hectares of the field, then a relationship may be found out amongst all the variables as:
Volume of water supplied = B*60*60*24 m3
Area of crop irrigated = D*104m2
Volume of water supplied per unit area = 86400/10000D= 8.64B/D
The duty of irrigation water depends upon a number of factors; some of the important ones are as follows:
i. Type of Crop:
As different crops require different amount of water for maturity, duties are also required. The duty would vary inversely as the water requirement of crop.
ii. Climate Season and Type of Soil:
Some water applied to the field is expected to be lost through evaporation and deep percolation.
Evaporation loss has a direct bearing on the prevalent climate and percolation may be during drier seasons when the water table is low and soil is also dry. Percolation loss would be more for sandy soils than silty or clayey soils.
iii. Efficiency of Cultivation Methods:
If the tillage and methods of water application are faulty and less efficient, then the amount of water actually reaching the plant roots would be less. Hence, for proper crop growth more water would be required than an equivalent efficient system. Also, if the water is conveyed over long distances through field channels before being finally applied to the field, then also the duty will rise due to the losses taking place in the channels.