Stevia cannot tolerate prolonged water stress and is susceptible to irreversible wilting. It cannot survive prolonged phase of water logging also. The plant prefers moist but drained soil condition. Thus drip irrigation is one of the most favoured irrigation systems for stevia. Drip irrigation has the following advantages.
Drip irrigation is one of the methods of irrigation that saves water and fertilizer. In drip irrigation method, water drips slowly to the roots of the plants either onto the soil surface or directly onto the root zone through a network of valves, pipes, tubing and emitters. The process is completed in narrow tubes so that water is given directly to the root of the plant. Drip irrigation is also termed as localized irrigation or micro irrigation.
Advantages of Drip Irrigation:
1. Maximum water use efficiency and crop yield.
2. No water is accessible to weeds.
3. High efficiency in the use of fertilizers.
4. Less weed growth and restriction of population of potential hosts.
5. Low labour requirement and relatively low operation cost.
6. No soil erosion.
7. Improved infiltration in soil of low intake.
8. Compatibility to sophisticated automatic control.
9. No runoff or seepage of fertilizers into ground water.
10. Less evaporation losses of water as compared to surface irrigation.
Disadvantages of Drip Irrigation:
1. The drip tubes are succeptible to clogging
2. uneven moisture distribution
3. Local Salinity hazards
4. High cost
5. Higher skill is required for design, installation and operation.
6. Rodent damage to drip lines
7. Drip irrigation might be unsatisfactory if herbicides or top dressed fertilizers need sprinkler irrigation for activation.
Drip irrigation is adaptable to any farmable slope. Normally the crop would be planted along contour lines and the water supply pipes (laterals) would be laid along the contour also. This is done to minimize changes in emitter discharge as a result of land elevation changes.
Drip irrigation is suitable for most soils. On clay soils water must be applied slowly to avoid surface water ponding and runoff. On sandy soils higher emitter discharge rates will be needed to ensure adequate lateral wetting of the soil.
Download FAO Document on Irrigation Water Quality
Suitable irrigation water
One of the main problems with drip irrigation is blockage of the emitters. All emitters have very small waterways ranging from 0.2-2.0 mm in diameter and these can become blocked if the water is not clean. Thus it is essential for irrigation water to be free of sediments. If this is not so then filtration of the irrigation water will be needed.
Blockage may also occur if the water contains algae, fertilizer deposits and dissolved chemicals which precipitate such as calcium and iron. Filtration may remove some of the materials but the problem may be complex to solve and requires an experienced engineer or consultation with the equipment dealer.
Drip irrigation is particularly suitable for water of poor quality (saline water). Dripping water to individual plants also means that the method can be very efficient in water use. For this reason it is most suitable when water is scarce.
Essential components of the drip irrigation system
Apart from a stable and good quality water source like bore well, river, surface water body etc. The other major components of a drip irrigation system are as follows :
The main pump should have the adequate water pumping capacity with at least 30 PSI pressure. Multiple impeller high discharge pumps are most suitable for this application. Both electrical pump of gas/diesel driven pump may be used. The major issue with the electrical pump is flow control, which is achieved with a back-flow line and two gate valves. In this system, a part of the water flow from the pump, which is sufficient to buildup the required pressure in the irrigation system is allowed to enter into it. The other part is channelized to the water source again through a back flow line and another gate valve.
Hydrocyclone Sand Separator :
A Hydrocyclone separates sand and other solid matter from water with very little head loss and 90% or better efficiency. There is no head loss build up and no clogging when the solids are separated. Hydrocyclones are easy to operate and maintain, and have no moving parts or screens. Versatility in system configurations and ease of installation are some of its great advantages. A Hydrocyclone uses a tangential injection flow process, enhancing the centrifugal forces and moving solid particles outwards. The dispersed particles move downward in a spiral path into an underflow chamber (sedimentation tank) while clean liquid moves upwards to the center of the spiral, towards the top outlet.
Gravel/sand filter :
These filters are effective against inorganic suspended solids, biological substances and other organic materials. This type of filter is essential for open reservoir, when algae growth take place. The dirt is stopped and accumulated inside the media in the filter. Gravel filter consist of small basalt gravel or sand (usually 1-2 mm dia) placed in cylindrical tank, made of metal. Water enters form the top and flows through the gravel while leaving the dirt in the filter. The clean water is discharge at the bottom. The filter is cleaned by reversing the direction of flow.
Screen filter :
Screen filters are probably the most common filters and in most cases the least expensive. Screen filters are excellent for removing hard particulates from water, such as sand. They are not so great at removing organic materials such as algae, mold, slime, and other unmentionables! These non-solid materials tend to embed themselves into the screen material where they are very difficult to remove. In other cases they simply slide through the holes in the screen by temporarily deforming their shape.
Pressure gauges :
Pressure gauges are required for monitoring line pressure in various places in the irrigation systems just to ensure that no component in the system is exposed to excessive mechanical forces.
Fertilizer dosing System:
The most effective way to increase the yield and quality of Stevia crop is by feeding the plant according to its specific, ever-changing needs. This means delivering the right amount of water and nutrient at the right time. This is achieved by a system which injects precise quantity of fertilizers into the irrigation system and the fertilizers are carried to the plant root zone with irrigation water. The systems available for this operation are as follows.
Hydraulic piston motor injector - Its linear hydraulic piston motor is powered by the hydraulic pressure in the irrigation system, and does not require any other energy source for injecting fertilizer into the pressurized irrigation line. Water enters the injector through the upstream inlet and exits it to the drain line through the water outlet. The fertilizer is injected at twice the pressure of the irrigation line, generated by the hydraulic piston motor itself. The liquid fertilizer enters the injector through the suction port positioned inside the fertilizer tank and is injected through the injection outlet, downstream, into the irrigation line.
Venturi Injector - A Venturi injector uses excess pressure in the irrigation system to create a low pressure zone, or vacuum, in the injector throat. This vacuum efficiently draws chemicals into the pressurized water line, eliminating the need for a separate chemical injection pump. Venturi injectors are the most cost-effective method of introducing chemicals into a pressurized irrigation system, popular because of their simplicity, reliability and low cost, and because they don’t require a power source.
Electronic Diaphragm Dosing Pump – This system uses a diaphragm pump driven by a precision servo motor to deliver precise quantities of into the irrigation line. This type of units are often controlled by a microcontroller, which senses the flow rate through the line and adjusts the fertilizer solution injection rate. The dosing pumps have small delivery rates and multiple pumps may be required for large irrigation installations.
Hydraulic fertilizer injector (proportional) - Applies fertilizers and chemicals proportionally to the water flow through an irrigation system in the slow and constant quantities required for steady growth. Widely used in open fields, orchards and landscaping to inject an additive into a water line at a consistent injection rate under varying water pressure and flow rates. This process, injecting additives using only water power, is accurate and simple. These systems areWater driven and fertilizer solution is added in proportion to water flow for accurate mixing.
The main line conveys the water from filtration system to the sub main. They are normally made of rigid PVC pipes in order to minimize corrosion and clogging. Usually they are placed below the ground i.e. 60 to 90 cm ( 2 to 3 ft) , so that they will not interfere with cultivation practices. Their diameter is based on the system flow capacity. The velocity of flow in mains should not be greater than 1.5 m/s and the frictional head loss should be less than 5ml /1000 m running length of pipeline.
The Submain conveys the water mainline to the laterals. They are also buried in ground below 2 to 2.5 ft and made of rigid PVC. The diameter of Submain is usually smaller than main line. There may be number of Submain from one mainline depending upon the plot size and crop type.
Laterals are small diameter flexible pipes or tubing made of low density polyethylene (LDP) or liner low density polyethylene (LLDPE) and of 12 mm, 16mm, and 20 mm size. Their colour is black to avoid the algae growth and effect of ultra- violet radiation. They can withstand the maximum pressure of 2.5 to 4 kg/cm2. They are connected to Submain at predetermined distance. The pressure variation between two extreme points of lateral should not be more than 15-20 % and discharge variation should not be more than 10%. On slopping ground, the laterals are placed along the contour with 1% extra length for sagging purpose.
Emitters or Drippers:
It is the main component of Drip irrigation system for discharging water from lateral to the soil. i.e. to the plants. There are various types and size of drippers, based on different operating principles. They are made of plastic, such as polythene or polypropylene. Their discharge range is between 1-15 lph. Each dripper has it’ s own characteristics, advantages and disadvantages which determines its use.
The drippers can be classified according to working principle, discharge, type, structure, working pressure, designation, durability, regulated and non regulated discharge.
The main principle when planning a dripper is to achieve the minimum discharge with maximum size of water passage.The large water passage is essential to minimize clogging and provide the minimum discharge for cheapest set-up. Therefore, an emitter is necessary, ( a hole in a pipe is not a dripper). Emitters may be on the lateral or inside to lateral, accordingly they are called on line or inline emitters.
Controls Valves (Ball Valves):
These are used to control the flow through particular pipes. Generally, they are installed on filtration system, mainline, and on all Submain. They are made up of gunmetal, PVC cast iron and their size ranges from ½” to more than 5”.
It is provided at the end of each sub main to flush out the water and dirt’s.
Air Release Cum Vacuum Breaker Valve:
It is provided at the highest point in the main line to release the entrapped air during the start of the system and to break the vacuum during shut off. It is also provided on Submain if Submain length is more.
Non Return Valve:
It is used to prevent the damage of pump from flow of water hammer in rising main line.
Gromate and Take-off:
These are used to connect the lateral to Submain. A hole is punched with hand drill of predetermined size in Submain. Gromate is fixed into the hole. Take off is pressed into the hole. Take off is pressed into the gromate with take of punch upto the step provided. Gromate acts as a seal. The sizes are different for 12 mm, 16mm, and 20 mm lateral.
End Caps (End Sets):
They are used to close the lateral ends, Submain ends or mainline ends. Sub mains and mains are preferably provided with flush valve. They are convenient for flushing the line.