Drip Irrigation System - An Overview
Dr. A.M. Michael
"Drip or trickle irrigation is an efficient irrigation method of recent origin, which is becoming increasingly popular in areas of water scarcity and poor quality irrigation water. In drip irrigation, water is applied frequently at low rates from a low pressure delivery system comprising of small diameter plastic pipes fitted with outlets, called emitters or drippers, directly to the land surface close to the plant where the roots grow. Drip irrigation is best suited to water scarcity areas and regions where irrigation water quality is marginal or low (saline water). Due to the frequent application of irrigation water, salts are pushed to the periphery of the moist zone, away from the root spread area. It is suitable to almost all types of soils. In clay soils with low infiltration rates, water is to be applied slowly to prevent surface water ponding and runoff. In sandy soils with high infiltration rates, higher dripper discharge rates will be required to ensure adequate lateral wetting of the soil. Drip irrigation is advantageous on lands with undulating topography without undertaking major land leveling operations and on slopes where the
Fig. 1. Profiles of moisture front advance in drip irrigation in medium
Figure - 2. Movement of salts to the periphery of the wetted bulb in point source of water application (drip irrigation).
(Source: Adapted from Lake Irrigation Co. Bakerfield, California, USA)
Soil depth is limited and the crop value is high. The labour requirement is low in drip irrigation. Drip irrigation is suitable for almost all orchard crops, plantation crops and most of the row crops. The method has been observed to be highly economical and beneficial in water scarcity areas to grow orchard and plantation like coconut, tea, coffee, cardamom, citrus, grapes, banana, papaya, mango, guava, pineapple and pomegranate; row crops like sugarcane, cotton, groundnut, sapota, strawberry and vegetable crops including tomato, potato and other widely spaced vegetable crops, and flower plants. It is highly suitable for nursery raising and establishment of forestry plantations, especially under the wasteland development programme. It is also suitable to irrigate sugarcane cotton and groundnut. However, from economic considerations, drip systems are not adapted to close growing field crops like cereals and pulses, as the number of laterals required are high which result in high costs of the system.
The terms drip irrigation, trickle irrigation and micro-irrigation are synonymous. Drip irrigation is a micro-irrigation method in which the rate of water application is very low and without any pressure, i.e., drop by drop. While drip irrigation and trickle irrigation have identical meaning, the term micro-irrigation encompasses other low pressure water application methods like microsprinkler, bubbler and spray systems in which water is emitted in the form of small sprinkling, tiny streams or miniature sprays through fixed diffusers or applicators, localizing the water on the soil in separate spots as well as indigenous methods of micro-level application of water to plants. The term localized irrigation is sometimes used in place of drip/trickle/micro-irrigation, as the systems cause wetting which is localized to the plant root zone. The devices for water application are in the form of emitters strip tubings, jets or minisprinklers. The service pressure of the system is of the order of 1 bar or less. Fertilizers and other chemicals can be applied efficiently to individual plants or a group of plants, using the drip system. Although the terms drip irrigation and trickle irrigation are used interchangeably.
Drip irrigation is based on the basic concept of irrigating only the root zone of the crop, rather than the entire land surface on which the crop is grown. Water flows from the emission points through the soil by capillarity and gravity. The soil moisture content of the crop root zone is maintained at near optimum levels to facilitate optimum crop growth and production. This will involve frequent applications of small quantities of water. Irrigating only a part of the land surface minimizes evaporation losses, reduces weed growth - especially in widely spaced crops and minimizes interruption of cultural operations like inter-cultivation and harvesting.
Major advantages of drip irrigation systems: The major advantages of drip irrigation, as compared to other methods of irrigation include the following:
- (i) Higher crop yields: Studies on crop performance with drip irrigation, in comparison to other irrigation methods have consistently shown yield increases ranging from 20 to 50% or more in drip irrigated crops, namely, fruit crops (banana, grapes, citrus, pomegranate, papaya, pineapple, watermelon and most other fruits), vegetable crops (cabbage, cauliflower, okra, tomato, potato, onion, chilli, radish, brinjal, bottle gourd, French bean and most other vegetable crops grown in the tropical, sub-tropical and temperate regions) and commercial crops like cotton and sugarcane. The increase in crop yield is mainly due to the maintenance of optimum soil moisture in the crop root zone throughout the growing period of the crop with the better control of irrigation water application in the drip system,
- (ii) Improved quality of the harvested produce of the crop:
Drip irrigation results in improved "quality of crop produce due to the maintenance of optimum soil moisture conditions in the root zone throughout the growing season, resulting in uniform crop growth. In addition, damage and loss due to water contact with foliage are eliminated, resulting in better quality of produce.
- (iii) Sayings in irrigation water: With the elimination of water application losses such as deep percolation, runoff and evaporation and reduction in the volume of the soil which is wetted (limited to the crop root zone), there is substantial saving in the amount of water required for irrigation, as compared to other methods of irrigation. Loss of water from the land surface which is not occupied by the crop is eliminated. As compared to sprinkler irrigation, the loss of water due to evaporation from the plant foliage is eliminated. Further, the losses in water conveyance such as seepage is eliminated with the adoption of drip method of water application, as compared to the unlined open channel water conveyance system commonly used in surface irrigation methods. The savings in the quantity of irrigation water resulting from the adoption of drip irrigation usually range from 20 to 50% or more, when compared to surface methods of water application and to a lesser extent when compared to sprinkler irrigation. Further, the irrigation water requirement of crops under drip irrigation is substantially low during the initial stages of crop growth. The saving in water by introducing large scale application of drip irrigation in a project area increases the irrigation command area of the project and provides opportunity for diversification of crops and introduction of high value' crops in the cropping system,
- (iv) Increased efficiency in fertilizer use: A drip irrigation system is an effective means of applying fertilizers and other plant nutrients into the crop root zone where they are needed. The efficiency in fertilizer application increases greatly when fertilizers and nutrients are applied with the drip system, as compared to other methods of water application.
- (v) Reduced energy consumption: Drip irrigation results in reduced energy requirement in pumping, compared to sprinkler irrigation, due to the low operating pressure required by the drip system. Further, the quantity of water required for irrigation is low under the drip system, which further reduces the energy requirement.
- (vi) Tolerance to windy atmospheric conditions: Wind has no adverse influence on drip irrigation, as compared to the sprinkler system. In the drip system, the laterals with the emitters are laid at the land surface and only the point of water application is wetted which is hot influenced by the wind. The evaporation loss from the land surface is also negligible, as the wetted area is under the plant foliage.
- (vii) Reduced labour costs: In irrigated agriculture using the drip system, the labour requirements are low due to reduced cost of field preparation, elimination of fertilizer application as a separate operation, low requirement of weeding and fewer harvesting rounds due to more uniform ripening of the crop.
- (viii) Improved disease and pest control: Plant diseases and pests are lower in drip irrigated crops, as compared to other methods of water application. Bacteria, fungi and other organisms are reduced as the 'above ground' plant parts remain dry. As the application of water is limited only to the crop root zone, the areas surrounding the plant remain dry and hence the weed growth in the crop field is greatly reduced. With little or no weed growth, the intensity of pest and disease incidence is reduced. With the elimination of surface runoff resulting from drip irrigation, the spread of disease causing organisms by water movement is reduced,
- (ix) Feasibility of irrigating undulating terrain and sloppy land: Hilly and undulating terrain cannot be irrigated with surface irrigation methods without extensive land levelling operations. Drip and sprinkler methods can be designed to operate efficiently on almost any topography without incurring the expenditure in land levelling. Drip irrigation can be designed to suit changing field gradients.
- (x) Suitability for problem soils: In heavy clay soils, with low infiltration rates, low rates of water application can be selected with the drip system to match the soil characteristics. On the other hand, in sandy soils with high infiltration rates, water can be applied in small quantities frequently, avoiding deep percolation losses,
- (xi) Improved tolerance to salinity: With the adoption of drip irrigation systems, it is possible to use more saline water for irrigation, as the root zone soil column is kept at higher level of moisture content, resulting in reduced soil moisture stress. The contact of water with the plant is minimized, compared to other methods of irrigation. In general, drip irrigation will reduce the sensitivity of most crops to saline soils and waters, due to its ability to maintain low water tension in the root zone. The frequent application of water with drip irrigation reduces the concentration of salts in the root zone by moving salts away from the root zone to the edges (perimeter) of the wetted bulb formed by the point source of water application in the drip system (Fig. 2). This process, called micro-leaching, prevents the harmful combination of high soil salinity and low moisture availability.
- (xii) Promotes congenial soil physical conditions in the root Zone : The maintenance of soil moisture at nearly constant and optimum levels by renewing the water supply to the root zone nearly at the same rate as it is used by the plant results in low soil suction and facilitates water and nutrient uptake by the plant and high soil hydraulic conductivity. The soil, on the other hand, is never saturated in a properly managed drip irrigation system, and adequate aeration is maintained throughout the growing period of the crop. The low rate of water application makes drip irrigation suitable even in soils with low infiltration characteristics. In comparison to sprinkler irrigation, where the losses due to over-irrigation and irrigating areas not occupied by crops, including field edge losses, (may be as high as 20% or more), these types of losses are almost eliminated in drip irrigation. Further, no water is lost due to the transpiration of weeds, as irrigation is limited to the crop. The drip system facilitates better control of the irrigation water supply, as compared to the sprinkler irrigation system. There is no formation of soil crust in drip irrigation,
- (xiii) Promotes better uniformity in irrigation water application: The large number of irrigation points (emitters) in a drip system provide better uniformity of application of water. Low discharges and low pressure heads in the water distribution network enable the use of smaller pipes of lower pressure ratings at reduced costs. Fertilizers, pesticides and other chemicals may be injected into the system and applied in small quantities, as needed, with irrigation water.
- (xiv) Easy in operation: Drip irrigation system is comparatively easy to operate. Irrigation can be continued throughout the day and the night, regardless of wind, daytime, temperature or cultural practices,
- (xv) Facilitates automation: Automation could be easily incorporated into the drip irrigation system
- (xvi) Adapted to irrigate crops in green houses: Drip irrigation system is well adapted to irrigate crops grown in covered green houses with no wetting of the walls or the cover.