In this innovative system water trickles drop by drop at or near the root zone of plants. This system can be water-efficient, if managed properly, since evaporation and runoff are minimised. In modern agriculture, drip irrigation is often combined with plastic mulch, to further reduce evaporation, and is also the means of delivery of fertiliser. The process is known as fertigation. In this system it is difficult to regulate pressure on steep slopes. However, pressure compensating emitters are available which if applied does not necessitate levelling of field.
High-tech solutions involve precisely calibrated emitters located along lines of tubing that extend from a computerised set of valves. The tubes are usually black (or buried under soil or mulch) to prevent growth of algae and to protect polyethylene from degradation due to ultraviolet light.
Drip irrigation system consists of the following components: Pump to lift water from the source of supply; a head unit consisting of a tank to maintain the required pressure for water circulation; a central distribution system connected with the main water supply system, which regulates water pressure and quantity; a fertiliser tank connected with the central distribution system to supply soluble plant nutrients with the irrigation water; a filter connected to the central distribution system to remove materials suspended in water; PVC main supply pipe of suitable diameter and length to deliver desired discharge; sub-main/or laterals of suitable diameter and length connected in parallel to the main, and plastic drippers inserted in the laterals at the desired spacing (equal to the intra-row spacing of the plant) which control the release of desired quantity of water.
Drip irrigation is applied at farms, commercial greenhouses, and residential gardens. This system is adopted extensively in areas where water scarcity is acute. The system is efficient for containerised landscape trees, grapes orchards, bananas, citrus fruits, strawberries, sugarcane, cotton, maize and tomato.
Because of the way water is applied in the drip system, traditional surface application of timed-release of fertiliser is sometimes ineffective, so drip system often mix liquid fertiliser with the irrigation water. This is called fertigation and chemigation (application of pesticides and other chemicals to periodically clean out the system, such as chlorine or sulphuric acid). Chemical injector such as diaphragm pumps, piston pumps are used for this purpose. Chemicals may be added constantly whenever the system is irrigating or at intervals. Fertiliser savings of up to 95 per cent have been reported from recent university field tests using drip fertigation and slow water delivery as compared to time-release and irrigation by micro spray heads.
Drip irrigation has proved to be a success in terms of water saving and increased yield in a wide range of crops. Following table gives the cost–benefit of drip irrigation in some crops.
The increase in yield ranged from 20 per cent to as high as 100 per cent. The highest increase in yield of 100 per cent has been reported in banana, 40-50 per cent in sugarcane, pomegranate, tomato and chillies and around 25 per cent in grapes and cotton. The saving in irrigation water compared to conventional method of irrigation was 40-70 per cent. The saving of water depends on crops, soil and environmental conditions. The main reason for saving of water are absence of conveyance and runoff losses, reduced evaporation due to lesser wetted area and minimum or no deep percolation.
Drip irrigation provides opportunity for enhanced plant growth and yield. It also provides sufficient amount of water throughout the growing season unlike other methods where soil moisture fluctuates from field capacity to different degrees of dryness between irrigation. This system reduces salinity hazard due to low salt concentration owing to high availability of water continuously.
Weed infestation is less with drip irrigation, because only a small area is wetted. Due to these advantages, the expenditure on drip irrigation can be recovered quickly. The payback period of investment in drip irrigation was from one to four years depending on the crop, vis-à-vis the life of the system which is around 10 years.
The following main advantages can be achieved through drip irrigation as compared to conventional irrigation methods: Saline water can be used; no fertiliser nutrients are lost due to localised application; high water distribution efficiency is achieved; levelling of the field is not necessary; only root zone is saturated; moisture in the root zone is always at field capacity; soil factor plays important role in the frequency of irrigation; no soil erosion takes place; the distribution of water is uniform controlled by each nozzle; labour cost is low; variation in supply can be maintained by regulating valves and drippers; moisture movement is two dimensional.
There are also some disadvantages in the application of drip irrigation which are as follows: Initial cost can be more than overhead systems; the plastic tubing and ‘tapes’ generally last 1-3 seasons; if water is not properly filtered and equipment not properly maintained clogging may take place; drip irrigation may be unsatisfactory if herbicides or top dressed fertilisers need sprinkler irrigation for activation; drip tape causes extra cleanup costs after harvest; time and harvest, if not installed properly, results in waste of water.
This system requires careful study of relevant factors like land irrigation system and its components. Its also has some social problems e.g. theft of components which is the main hurdle in the expansion of this system among the farming community.
SUBSIDY: The government has recently announced Rs16 billion subsidies on drip irrigation farming spread over five years, to cover 200,000 acres of cash crop land. Importers were asked to tie up with international companies of repute.