5.10 Drip irrigation - India

Introduction

Drip irrigation is of recent origin, and, in India, is being used on a limited scale in Tamil Nadu, Karnataka, Kerala and Maharashtra States, mainly for coconut, coffee, grape and vegetable production. Drip irrigation systems (DIS) are extremely effective in arid and drought prone areas where water is scarce, and have been used experimentally in India for over 15 years: in the States of Tamil Nadu, Karnataka, Maharashtra, and Andhra Pradesh, progressive farmers started using this method of irrigation in the late-1970s without the benefit of any subsidies or support from central or state governments. However, as a result of subsequent, sustained efforts by the state and central governments, agricultural universities, and private sector manufacturers, use of drip irrigation systems spread through the drought prone areas of southern and western India. The use of DIS, however, is primarily to irrigate high value, horticultural crops. In states like Maharashtra, Karnataka, and Tamil Nadu, DIS are sometimes used for irrigation of vegetable and other commercial crops. The sharp rise in the area under DIS irrigation between 1988 and 1989 is due, in large part, to the significant increase in the use of these systems in the Maharashtra State.

Technical Description

Drip irrigation systems deliver water and agrochemicals (e.g., fertilizers and pesticides) directly to the root zones of the irrigated plants at a rate best suited to meet the needs of the plants being irrigated. Thus, this system makes efficient use of water, especially when compared to conventional methods of irrigation such as furrow, border, basin and sprinkler irrigation systems, which, under arid and drought conditions, suffer from an high rate of water loss and have a low degree of water use efficiency.

Extent of Use

Drip irrigation systems are used throughout the arid parts of India, especially in Maharashtra, Haryana, Meghalaya, and Rajasthan. At Rahuri, in Maharashtra State, the use of drip irrigation of pomegranates, grown in gravely soils, resulted in a savings of about 44 cm of irrigation water, or 44%, over the conventional check basin irrigation systems previously used, as shown in Table 43. The water use efficiency was also much higher using the drip method of irrigation, especially when combined with the use of mulch, which effected a further savings of irrigation water of 14% when compared to un-mulched plots. Similarly, at Dapoli in the Konkan Region of Maharashtra State, where, despite an annual rainfall of about 4 000 mm, the period between December and May is often a time of severe drought, drip irrigation systems were used to irrigate mango and cashew crops. The soils of the Region are highly porous laterites, which are poorly suited to supporting conventional, pond-fed irrigated agriculture, particularly of row crops. Nevertheless, the Region has an high potential for the production of crops like mangoes and cashews. However, to establish mango or cashew orchards, it is essential to provide adequate water during the first two to three years after transplanting the seedlings, which, during the dry season, can only be supplied through irrigation, In the mango orchards, an indigenously designed drip irrigation system was installed using a common, earthen pitcher placed at an higher elevation than the plants and a siphon to direct the water to the trees by means of two to three drippers per stem. This system helped to quickly establish the orchards, with a considerable savings in irrigation water compared to prevalent practice of hand watering the trees. As shown in Table 44, there was also substantial improvement in plant growth, as measured by height, girth, and plant spread, using drip irrigation compared to the conventional hand watering method. The application of about 45 I/plant/week of water appeared optimal.

In Haryana and Rajasthan States, drip irrigation of potatoes grown in loamy sand soils at Jobner, of onions, sugar beets, and potatoes grown in sandy loam soils at Hissar, and of bhindi and sugarcane grown in clay soils at Rahuri (clay soil) resulted in improved crop yields and a savings in irrigation water of between 18% and 40%, except at Jobner where few differences were apparent between irrigation methods used. Nevertheless, there was substantial improvement in the water use efficiency of the crops at all three centres.

TABLE 43. Yield of Pomegranates Using Different Irrigation Methods on Gravel Soils.

TABLE 44. Effect of Drip Irrigation on the Growth of Mango Plants.

Similarly, at Hissar, the use of drip irrigation systems supplied with irrigation water from a poor quality source (having an electrical conductivity of 6.5 mmhos/cm) resulted in only a 12% decrease in the yield of radishes using drip irrigation compared to surface irrigation methods using the same poor quality source water, which resulted in a decrease in yield of 39.5%. Even under these conditions, water use efficiency increased almost threefold with drip irrigation compared to conventional surface irrigation techniques as shown in Table 46. A well-managed drip irrigation system supports the use of poor quality of water because the irrigation water is applied continuously, ensuring that the root zone does not dry out and that the salts move away from the root zone. Thus, the accumulated salt is leached to the edge of the wetted soil mass where it does not interfere with the growth of the plants. Also, since a much smaller quantity of water is applied to the soil, the total salt load applied is likewise lower.

TABLE 45. Yield of Radishes Using Drip Irrigation.

TABLE 46. Yield of Brinjals Using a Salt Water Drip Irrigation System.

In Meghalaya, some of the tribal farmers use a drip irrigation system constructed of bamboo to irrigate betel, pepper and arecanut crops. The system is indigenously designed using locally available materials. The hillsides on which this system is used have a rock and soil mixture with poor water holding and retention capacities that require frequent applications of irrigation water. Using this system, water from natural stream is diverted at a point of higher elevation than the plot to be irrigated, and is conveyed by gravity through bamboo channels, supported on ground surface by wooden or bamboo supports, to the point of application. The discharge at the head channel varies from 15 to 20l/min and is reduced to between 10 and 30 drops/min at the point of irrigation water application. The elevation of the head channel may be up to a few metres higher than the irrigated field elevation, whereas the elevation of the last channel may be less than 10 cm to 15 cm above the ground surface.

At Jobner in Rajasthan, earthen pitchers and porous cups have been used successfully for irrigating vegetable crops, such as crops of cabbage, cauliflower, and knolkhol. The technique uses earthen cups of 500 ml capacity embedded in the soil at the site of the seedlings. The cups are filled to the brim with water at intervals of 4 to 5 days. Because of their underground situation, the cups experience little water loss due deep percolation and/or evaporation. At Karnal, using a similar technology, earthen pitchers of about 15 l capacity have been used for irrigating cucumbers and radishes. This technology provides irrigation water to the crops at a rate of less than 2 cm/ha. These innovative technologies permit the cultivation of vegetables and cash crops in areas where it is not practical or possible to grow crops using conventional surface irrigation methods.

Operation and Maintenance

The principle operation and maintenance requirements associated with the implementation of this technology include the need for regular cleaning of the system and careful monitoring of the quality of the source water, as the drip irrigation systems are very sensitive to the clogging of the drippers. The systems also require a relatively high degree of skill to design, install and operate, and are susceptible to theft, damage and disruption by rodents that destroy the drip pipes and drippers.

Level of Involvement

The use of this technology requires skilled personnel. Because of the relatively high capital cost of the piping systems necessary to implement this technology, the initial funding for the project may require some level of government involvement. Regular operation and maintenance of the system is the responsibility of the individual operator.

Costs

The capital costs involved in the establishment of a drip irrigation system are high compared to the costs of establishing conventional irrigation systems. However, the labour requirements and operational costs are low. The net result is that the benefit-cost ratio for DIS is very favourable compared to conventional systems since the payback period for investment very short. In the case of the orchard crops in Maharashtra, the cost of DIS ranged from $450/ha to $1 150/ha in 1990. Elsewhere, the cost of using drip irrigation systems for sugarcane irrigation averaged $715/ha, for banana irrigation $1 150/ha, and for cotcrus-fruit irrigation $575/ha, with the payback periods ranging from 2 months for banana crops, 12 months for cotcrus-fruit crops, and 18 months for surgarcane crops. Comparative benefit-cost ratios for various crops ranged from 1.64 for groundnuts (peanuts), to 4.84 for pomegranates, to 5.15 for tomatoes, to 8.58 for grapes, to 15.0 for mosambi. These ratios compare to benefit-cost ratios of 1.80, 2.20, 3.96, 6.38, and 9.81, respectively, using conventional irrigation systems.

Effectiveness of the Technology

In almost all of the cases reported, excepting the Jobner case, there was an improvement in crop yields and savings in water use of between 18% and 40%. Consequently, there was a substantial improvement in the water use efficiency that ranged up to three times that of water use efficiencies achieved using conventional surface irrigation methods, even with the use of poor quality irrigation water. Because of the directed delivery of irrigation water, it is possible to utilize poor quality irrigation water using the drip irrigation system. The performance of this technology is summarized in Tables 40 and 41. The data presented in Table 40 are based upon water savings and increased yields achieved in Maharashtra State using drip irrigation systems. In addition to the improved yields and water savings, for crops such as sugarcane there is a savings in labour costs that equals the savings in water.

Advantages

The advantages of drip irrigation systems include an high efficiency of water use and greater crop yields compared to other irrigation methods. In addition, crops irrigated using drip irrigation systems generally require less tillage and are of better quality. DIS also contribute to improved plant protection and reduced occurrences of plant diseases and greater efficiencies in the use of fertilizers, because water containing the agrochemicals is applied directly to the plant roots in the quantities necessary for optimal plant production. For a similar reason, DIS can also make use of lower quality water, and results in no return flows, tail water losses or increased soil erosion. Because water is applied in optimal quantities, plants generally have a shorter growing season and produce fruit earlier, with less weed growth and pest damage than conventionally irrigated crops. The lower labour requirements result in relatively low operational costs, with savings in labour of up to 90% of the costs associated with conventional systems, in part, because mechanical operations can be carried out simultaneously with the application of irrigation water. DIS can be used in hilly terrain and on lands with problem soils, and results in improved infiltration in soils with low conductivity. Drip irrigation systems are low pressure systems, which can be adapted for use in greenhouses, and with automated control systems.

Disadvantages

Drip irrigations systems have a sensitivity to the clogging of the drippers, which may require pretreatment of turbid source waters, and, if not properly installed, can cause moisture distribution problems. The systems are also susceptible to rodent damage. The systems have an high cost compared to conventional irrigation methods, and require higher levels of skill for design, installation, and operation, which make them liable to damage or theft.

TABLE 47. Water Savings and Increased Yields Achieved Using Drip Irrigation.

TABLE 48. Effect of Irrigation Method on Crop Yield and Water Savings.

Further Development of the Technology

This is a proven technology suitable for use with high value crops. Several crops which can be irrigated using drip irrigation systems include sugarcane, groundnuts or peanuts, coconuts, cotton, coffee, grapes, potatoes, and all fruit crops, spaced vegetable crops, and flowers.

Information Sources

R.S. Saksena, Consultant Planning Commission and Chief Engineer (MI, Retd.), Ministry of Water Resources, Government of India, New Delhi.