Globally, fresh water at a tune of 3,240 M km3 is being utilized. Of this, 69% is being used in agriculture sector, 8% in domestic, 23% in industrial and other sector. In India, around 88% water is being used in agriculture sector, covering around 85Mha area under irrigation. Due to liberalization of industrial policies and other developmental activities, the demand for water in industrial and domestic sectors is increasing day by day, which forces to reduce the percentage area under irrigation. The growing demand from the population calls for more efforts to enhance agricultural production. The horticulture sector has emerged as a promising area for diversification in agriculture on account of high income generation for unit area, water and other farm inputs and environmental friendly production systems. Government of India accorded high priority for development of this sector since VIII plan by enhancing the Plan Grant from Rs 24 crores in VII plan to Rs 1000 crores.

Efforts were initiated to develop irrigation potential from the first five-year plan. The present total irrigated area in the country is about 40% of the total sown area. The conventional system of irrigation employing different methods like flooding, furrow, basin and border irrigation revolve around the concept of replenishing the moisture level to field capacity only after depletion by 50-60% of field capacity. These surface methods of irrigation have several disadvantages as listed below.

Presently, the problem facing the country is not the development of water resources, but their management in a sustainable manner. The need of the day is to economize water in agriculture and to bring more area under irrigation, reduce the cost of irrigation on unit land and increase the yield per unit area and unit quantum of water. This can be achieved only by introducing advance irrigation methods like microirrigation. This when done will not only improve the water productivity, but also results in arresting the water logging and secondary salinization problems of the canal command areas and check the receding water table and deteriorating water quality in the command areas.

The modern methods of irrigation have surely number of advantages over the conventional irrigation methods like border, check basin, furrow or surge irrigation. Table 1.2 shows some of the important points of differences between modern and other methods of irrigation.

Drip irrigation was developed originally as a sub-irrigation system and this basic idea underlying drip irrigation can be traced back to experiments in Germany in 1860's. The first work in drip irrigation in the U.S.A was a study carried out by House in Colorado in 1913. An important breakthrough was made in Germany way back in 1920 when perforated pipe drip irrigation was introduced.

During the early 1940's Symcha Blass, an engineer from Israel, observed that a big tree near a leaking tap exhibited more vigorous growth than other trees in the area. This led him to the concept of an irrigation system that would apply water in small quantity literally drop by drop. Around 1948, greenhouse operators in the UK began to try a similar method with some modifications. The earliest drip irrigation system consisted of plastic capillary tubes of small diameter (1 mm) attached to 1arge pipes. One of the refinements made by Blass in his original system was coiled emitter. In the early 1960's, experiments in the Israel reported spectacular results when they applied the Blass system in the desert area of the Negev and Arava.

Drip irrigation pipes began to be sold outside Israel in 1969 on commercial basis. Drip irrigation unit in their current diverse forms were installed widely in U.S.A, Australia, Israel, Mexico and to a lesser extent in Canada, Cyprus, France, Iran, New Zealand, UK, Greece and India.

In India drip irrigation was practised through indigenous methods such as perforated earthenware pipes, perforated bamboo pipes and pitcher/porous cups. In Meghalaya some of the tribal farmers are using bamboo drip irrigation system for betel, pepper and arecanut crops by diverting hill streams in hill slopes. Earthenware pitchers and porous cups have been used for growing vegetable crops in Rajasthan and Haryana. In India drip irrigation was introduced in the early 70's at agricultural universities and other research institutions. The growth of drip irrigation has really gained momentum in the last one decade.

These developments have taken place mainly in areas of acute water scarcity and in commercial/horticultural crops, such as coconut, grapes, banana, fruit trees, sugarcane and plantation crops in the states of Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu and Gujarat.

In 1981, the Government of India constituted National Committee on the Use of Plastics in Agriculture (NCPA) under the Ministry of Chemicals and Petrochemicals. Later NCPA was re-christened as National Committee on Plasticulture Applications in Horticulture (NCPAH) in 2001 in the Ministry of Agriculture under the Department of Agriculture & Cooperation with Hon’ble Minister of Agriculture as its Chairman.

The NCPAH has dedicated more than two decades in the development and promotion of plasticulture applications in the country, which included drip and sprinkler irrigation.

Since its inception, NCPAH made many recommendations to the Government. One of the recommendations was establishment of 17 Precision Farming Development Centres all over the country in various agro climatic zones to undertake development trials, demonstration of technologies and training of farmers and departmental officers and recommend package of practices on Plasticulture applications. Considering high cost of Plasticulture applications, on the recommendation of NCPAH, the Government of India started providing subsidy to farmers and other eligible beneficiaries for adoption of these applications.

Since then, GOI is providing subsidy to farmers for the plasticulture applications in water management (drip and sprinkler), greenhouse technology and plastic mulching and other Plasticulture applications. The subsidy is channelised through state directorate of horticulture/agriculture. The NCPAH is assisting the GOI in formulating the plan for horticultural development and implementing the subsidy schemes.

Microirrigation is frequent application of water directly on or below the soil surface near the root zone of plants. It delivers required and measured quantity of water in relatively small amounts slowly to the individual or groups of plants. Water is applied as continuous drops, tiny streams, or fine spray through emitters placed along a low-pressure delivery system. Such system provides water precisely to plant root zones and maintains ideal moisture conditions for plant growths.
The available literature and the results obtained at Precision Farming Development Centre, IIT Kharagpur and other research centres report that there is 50 to 70% saving in irrigation water and 18 to 152 % increase in yield of fruits and vegetable crops through drip irrigation. Table 1.4 shows the extent of water saving and increase in yield with drip irrigation system.

a) Gravel or Media Filter: Media filters consist of fine gravel or coarse quartz sand, of selected sizes (usually 1.5 – 4 mm in diameter) free of calcium carbonate placed in a cylindrical tank. These filters are effective in removing light suspended materials, such as algae and other organic materials, fine sand and silt particles. This type of filtration is essential for primary filtration of irrigation water from open water reservoirs, canals or reservoirs in which algae may develop. Water is introduced at the top, while a layer of coarse gravel is put near the outlet bottom. Reversing the direction of flow and opening the water drainage valve cleans the filter. Pressure gauges are placed at the inlet and at the outlet ends of the filter to measure the head loss across the filter. If the head loss exceeds more than 30 kPa, filter needs back washing. Fig. 1.2 shows different types of media filters.

b) Screen Filters: Screen filters are always installed for final filtration as an additional safeguard against clogging. While majority of impurities are filtered by sand filter, minute sand particles and other small impurities pass through it. The screen filter, containing screen strainer, which filters physical impurities and allows only clean water to enter into the micro irrigation system (Fig. 1.3). The screens are usually cylindrical and made of non-corrosive metal or plastic material. These are available in a wide variety of types and flow rate capacities with screen sizes ranging from 20 mesh to 200 mesh. The aperture size of the screen opening should be between one seventh and one tenth of the orifice size of emission devices used.

c) Centrifugal Filters: Centrifugal filters are effective in filtering sand, fine gravel and other high density materials from well or river water. Water is introduced tangentially at the top of a cone and creates a circular motion resulting in a centrifugal force, which throws the heavy suspended particles against the walls. The separated particles are collected in the narrow collecting vessel at the bottom. Fig.1.4 shows different types hydro cyclone/centrifugal filters.

d) Disk Filters: Disk filter (Fig. 1.5) contains stacks of grooved, ring shaped disks that capture debris and are very effective in the filtration of organic material and algae. During the filtration mode, the disks are pressed together. There is an angle in the alignment of two adjacent disks, resulting in cavities of varying size and partly turbulent flow. The sizes of the groove determine the filtration grade. Disk filters are available in a wide size range (25-400 microns). Back flushing can clean disk filters. However they require back flushing pressure as high as 2 to 3 kg/cm2.

4. Pressure relief valves, regulators or bye pass arrangement: These valves may be installed at any point where possibility exists for excessively high pressures, either static or surge pressures to occur. A bye pass arrangement is simplest and cost effective means to avoid problems of high pressures instead of using costly pressure relief valves.

5. Check valves or non-return valves: These valves are used to prevent unwanted flow reversal. They are used to prevent damaging back flow from the system to avoid return flow of chemicals and fertilizers from the system into the water source itself to avoid contamination of water source.

The mainline transports water within the field and distribute to submains. Mainline is made of rigid PVC and High Density Polyethylene (HDPE). Pipelines of 65 mm diameter and above with a pressure rating 4 to 6 kg/cm2 are used for main pipes..

Submains distribute water evenly to a number of lateral lines. For sub main pipes, rigid PVC, HDPE or LDPE (Low Density Polyethylene) of diameter ranging from 32 mm to 75 mm having pressure rating of 2.5 kg/cm2 are used.

They function as energy dissipaters, reducing the inlet pressure head (0.5 to 1.5 atmospheres) to zero atmospheres at the outlet. The commonly used drippers are online pressure compensating or online non-pressure compensating, in-line dripper, adjustable discharge type drippers, vortex type drippers and micro tubing of 1 to 4 mm diameter. These are manufactured from Poly- propylene or LLDPE.

A) Online Pressure Compensating drippers: A pressure compensating type dripper supplies water uniformly on long rows and on uneven slopes. These are manufactured with high quality flexible rubber diaphragm or disc inside the emitter that it changes shape according to operating pressure and delivers uniform discharge. These are most suitable on slopes and difficult topographic terrains.

B) Online Non-Pressure Compensating drippers: In such type of drippers discharge tends to vary with operating pressure. They have simple thread type, labyrinth type, zigzag path, vortex type flow path or have float type arrangement to dissipate energy. However they are cheap and available in affordable price.

C) In-Line Drippers or Inline tubes: These are fixed along with the line, i.e., the pipe is cut and dripper is fixed in between the cut ends, such that it makes a continuous row after fixing the dripper. They have generally a simple thread type or labyrinth type flow path. Such types of drippers are suitable for row crops.
Inline tubes are available which include inline tube with cylindrical dripper, inline tubes with patch drippers, or porous tapes or biwall tubes. They are provided with independent

pressure compensating water discharge mechanism and extremely wide water passage to prevent clogging.

The planning and design of drip irrigation system is essential to supply the required amount of irrigation water. The water requirement of the plant per day depends on the water that is taken by the plant from the soil and the amount of water evaporating from the soil in the immediate vicinity of the root zone in a day. The plant intake is affected by the leaf area, stage of growth, climate, soil conditions etc. The water requirement and irrigation schedule can be determined from the soil or plant indicators based methods or soil water budget method, but the simplest and most commonly method is to use pan evaporimeter data. To apply the required amount of water uniformly to all the plants in the field, it is essential to design the system to maintain desired hydraulic pressure in the pipe network. The design of Microirrigation system is essentially a decision regarding selection of emitters, laterals and manifolds, sub main, main pipeline and required pumping unit. The steps needed to be followed for designing the Microirrigation system are given below:

General information on water source, crops to be grown, topographic condition, type and texture of the soil and climatic data are essential for the design of the Microirrigation system.

Based on the available data of water capacity, water requirement of the plant, pressure required at the lateral, etc., layout designs are made by taking case of head loss, the layout design can be made as shown in Fig 1.6

The ideal micro-irrigation system is one in which all emitters (orifices) deliver the same volume of water in a given time. From the practical point of view, it is almost impossible to achieve this ideal performance. However, the flow variation of water pressure can be controlled by the hydraulic design.

The size of mains, sub mains, laterals and pump are decided based on the desired flow rate and pressure head in the system. The pressure drop due to friction can be generally evaluated with the help of William Hazen or Dacy-Weishbach equation. The procedure for

computation of head loss in lateral, sub main, main pipes and horsepower requirement of pump are given in this section.

Head Loss in Laterals
The pipes used in micro-irrigation system are made of plastics and considered as smooth pipe. The pressure drop due to friction can be evaluated with the help of Hazen -William empirical equation as given below.

As the length of the pipe increases, the discharge in the pipe decreases due to emission outlets and hence the total energy drop is less than as given by the above equation. For this reason, a reduction factor F is introduced

The design criteria for lateral pipe are to keep pressure variation and discharge variation within the prescribed limit. For lateral design, the discharge and operating pressure at the emitter are required to be known. Based on this, the allowable head loss can be calculated using above formula. The diameter of lateral pipe is usually selected such that the difference in discharge between emitter operating simultaneously will not exceed 10%. Pressure head difference should not exceed 10 to 15% of the operating pressure. For the discharge variation of 10%, the emission uniformity has to be more than 90%.

The submains line hydraulics is similar to that of the lateral hydraulics. The sub main hydraulics characteristics can be computed by assuming the laterals are analogous to emitters

on lateral line. Hydraulics characteristics of sub main and main line pipe are usually taken hydraulically smooth since PVC and HDPE pipe are normally used. The Hazen Williams roughness coefficient is usually taken between 140 and 150. The energy loss in the sub main can be computed with the methods similar to those used for lateral computations.

Usually the pressure controls or adjustments are provided at the sub main inlet. Therefore energy losses in the main line should not affect system uniformity. There is no outlet in case of main line therefore reduction factor is not multiplied. The frictional head loss in main pipeline is calculated by the same Darcy-Weisbach formula or Hazen-Williams formula.

Example 1 Design a drip irrigation system for a citrus orchard of 1 ha area with length and breadth of 100 m each. Citrus has been planted at a spacing of 5 m ? 5.5 m. The maximum pan evaporation during summer is 8 mm/day. The other relevant data are given below:

Emitters are selected based on the soil texture and crop root zone system. Assuming three emitters of 4 lph, placed on each plant in a triangular pattern are sufficient so as to wet the effective root zone of the crop.
Total discharge delivered in one hour = 4 x 3 = 12 lph
Irrigation time = 50 / 12 = 4 h 10 minutes

A well is located at one corner of the field. Submains will be laid from the centre of field (Fig 1.7). Therefore, the length of main, submains, and lateral will be 50 m, 97.25 m, 47.5 m each respectively. The laterals will extend on both sides of the submains. Each lateral will supply water to 10 citrus plants.
Total number of laterals = (100/5.5) x 2 = 36.36 (Considering only 36)
Discharge carried by each lateral, Qlateral = 10 x 3 x 4 = 120 lph
Total discharge carried by 36 laterals = 120 x 36 = 4320 lph
Each plant is provided with three emitters, therefore total number of emitters will be 36 x 10 x 3 =1080

Once the discharge carried by each lateral is known, then size of the lateral can be determined by using the Hazen- Williams equation (7)
The reduction factor (F) can be estimated as

Estimated head loss due to friction in the submain is much less than the recommended 20% variation, hence reducing the pipe size from 50 to 35 mm will probably be a good option.

Fertigation is the method of application of soluble fertilizer with irrigation water. Fertigation is a prerequisite for drip irrigation. Since the wetted soil volume is limited, the root system is confined and concentrated. The nutrients from the root zone are depleted quickly and a continuous application of nutrients along with the irrigation water is necessary for adequate plant growth. Fertigation offers precise control on fertilizer application and can be adjusted to the rate of plant nutrient uptake.

1.6.2 Equipment and Methods for Fertilizer Injection: Injection of fertilizer and other agrochemicals such as herbicides and pesticides into the drip irrigation system is done by i) By-pass pressure tank ii) Venturi system and iii) Direct injection system.

3). Direct injection system: With this method a pump is used to inject fertilizer solution into the irrigation line. The type of pump used is dependent on the power source. The pump may be driven by an internal combustion engine, an electric motor or hydraulic pressure. The electric pump can be automatically controlled and is thus the most convenient to use. However its use is limited by the availability of electrical power. The use of a hydraulic pump, driven by the water pressure of the irrigation system, avoids this limitation. The injection rate of fertilizer solution is proportional to the flow of water in the system. A high degree of control over the injection rate is possible, no serious head loss occurs and operating cost is low. Another advantage of using hydraulic pump for fertigation is that if the flow of water stops in the irrigation system, fertilizer injection also automatically stops. This is the most perfect equipment for accurate fertigation.

Two injection points should be provided, one before and one after the filter for fertigation. This arrangement helps in by-passing the filter if filtering is not required and thus avoids corrosion damage to the valves, filters and filter-screens or to the sand media of sand filters.

The ratio of N, P and K in fertilizer compounds varies with different fertilizers components. If the nitrogen content of a given fertilizer is X per cent, the actual amount of fertilizer A (kg of compound per application) to be applied per application is

where F1 is the fertilizer application rate per irrigation (kg/ha), A is the area irrigated (ha), c is the concentration of the fertilizer solution (kg/l), T is the duration of irrigation (h) and tr is the ratio between fertilizing time and irrigation time.

If a total 120 kg of N, 60 kg of P and 60 kg of K is to be applied in an area of 1 hectare in 20 applications, the amount of fertiliser to be applied during each application, P (kg/application) :

Example 3 A drip irrigation system is installed in 2 ha area under citrus crop. The plants are spaced at 5 m ? 5.5 m apart. Urea – ammonium nitrate, a liquid fertilizer with 32% nitrogen and weighing 1.32 kg/l is available for fertigation. Find the fertilizer injection rate to apply 60 kg/ha of elemental nitrogen. The irrigation and fertilizing time are 10 h and 5 h respectively.

i) Installation of pumping unit: Generally centrifugal pump is used in microirrigation system. The centrifugal pump is installed as close to the water surface as possible. It is located at an easily accessible place in clean, dry and well ventilated surroundings. To ensure maximum capacity, the site selected should permit the use of the shortest and most direct suction and discharge pipes. The foundation should be rigid enough to absorb all vibrations. The pump and driver must be carefully aligned. The suction piping should be as direct and short as possible. It should have minimum of fittings so as to avoid excessive friction losses. The use of bends, elbows, tees and other fittings is kept to the minimum to reduce head loss in the discharge line.

ii) Installation of fertigation unit: Water soluble fertilizer/chemical is injected into microirrigation system through fertilizer tanks, venturi type meter or injection pumps. The fertilizer tank/venturi injector or injection pump is connected parallel to the irrigation pipe line by creating differential pressure. Non-return valve is installed to prevent contamination of water source.

iii) Installation of Filter Unit: The following points should be considered for fixing the position of filter unit.

a) Minimum use of fitting such as elbows and bends to be made.
b) The filter unit should be fixed on the delivery side of the pump.
c) Care should be taken to see that the filter size should be in accordance with the capacity of the system.

iv) Installation of Mains and Sub mains: Except for fully portable system, both mains and sub mains are installed underground at a minimum depth of about 0.5 m such that they are unaffected by cultivation or by heavy harvesting machinery. Even for systems, which have portable laterals that are removed at the end of each season, it is common practice to install permanent underground sub mains. Generally sub mains run across the direction of the rows.

v) Laying of Laterals: Generally laterals are laid on the ground surface. Usually laterals are placed along contours on sloping field. Burying laterals underground might be necessary or at least have some advantages for some installations. Where this is done, the emission devices should be above ground level. The downstream end of the lateral can be closed by simply folding back the pipe and closing it with a ring of larger diameter pipe, known as end plug. This can be easily slipped for flushing. The simplest connection for low-pressure system is for the lateral to be inserted directly into the sub main. Slightly undersized hole in the sub main is cut with the help of twist meter drill bit. The hole is expanded with the

Example 4 Estimate the emission uniformity (EU) of emitters for a drip irrigation sub-main unit with the following field data. Given time (sec) required to fill a 100 ml container from 24 individual emitters are 64, 79, 67, 71,75, 81,68,85,75,69,85, 77,89,68,81,90,65,61, 72,78,80,70,74 and 68
Solution:
Individual emitter discharges (ml/s):
1.56,1.27,1.49,1.41,1.33,1.23,1.47,1.18,1.33,1.45,1.18,1.30,1.12,1.47,1.23, 1.11, 1.54, 1.64, 1.39, 1.28, 1.25, 1.43, 1.35 and 1.47

Filter is the heart of a drip system and its failure will lead to clogging of the entire system. Pressure differential across the filter is the correct indication of the timing of cleaning of the filter.

Sometimes silt escapes through the filters and settles in sub mains and laterals. Also some algae and bacteria lead to the formation of slimes/pastes in the pipe and laterals. To remove them, the sub mains should be flushed by opening the flush valves. The lateral lines are flushed by removing the end caps. By flushing, even the traces of accumulated salts will also be removed. The flushing is stopped once the water going out is cleaned.

Clogging or plugging of emitters/orifices of bi-wall will be due to precipitation and accumulation of certain dissolved salts like carbonates, bi-carbonates, iron, calcium and manganese salts. The clogging is also due to the presence of microorganisms and the related iron and sulphur slimes due to algae and bacteria.
The clogging or plugging is usually avoided / cleared by chemical treatment of water. Chemical treatment commonly used in micro-irrigation systems includes addition of chloride and/or acid to the water supply. The frequency of chemical treatment depends on degree of problem at the site. As a general rule, acid treatment should be performed once in ten days and chlorine treatment once in fifteen days.

the system is shut off for 24 hours. After that the lateral end caps and flush valves are opened to flush out the water with impurities. The bleaching powder can directly be injected through venturi at the rate of 2 mg/l.

The cost of drip system depends on the type of crop, spacing, water requirement, proximity to water source etc. The cost estimation has been done for installing drip irrigation system for few important crops by considering the cost of components supplied by the manufacturer for the land holdings of one acre( 0.4 ha). The cost estimation for installation of drip system for Coconut, Aonla, Banana, Tomato, Okra and Chilli crops are worked out and are as given below. The life of the drip system components usually lasts 5 years for laterals and emission devices and about 10 years for mains and submains. The cost of materials of drip irrigation system is given in Table 1.8 and cost estimation for different crops (Coconut, Aonla, Banana, Tomato, Okra, Chillies) is given in Table 1.9 and Table 1.10.