Subsurface Drip Irrigation System (SDI)
Rain-fed agriculture in Kenya is becoming increasingly unreliable especially in the drier areas where the issue is more about getting water, than it is about managing the water resources.
Thus in this article, we will explore an irrigation method that is centered on saving water and nutrients by allowing water to drip slowly to the roots of plants.
The Subsurface Drip Irrigation (SDI) system is a variation from conventional surface drip irrigation techniques in that laterals/pipes are buried beneath the ground.
Farmers all around the globe are quickly adopting this form of irrigated agriculture as a guard against uncertainties such as the amount and distribution of rain. In China, India, Israel and the USA, irrigated agriculture has widely been a magic bullet which has transformed the regions from net food importers to food exporters.
This technology has enabled a country such as Israel, a country that can fit into Garissa County twice, to feed the world. The SDI system is superior to the conventional methods of irrigation in various ways:
- High degree of uniformity of application as it is controlled by the output of each nozzle.
- Evaporation is reduced.
- The amount of water can be fine-tuned. This avoids water loss caused by runoff or evaporation.
- Frequent irrigation allows for optimum soil moisture content in the root zone.
- Great performance in windy and arid locations.
- If pre-treated wastewater is used for irrigation, the risk of direct contact with crops and labourers is reduced.
- Fertilizer and nutrient loss is minimized due to a localized application and reduced leaching.
- Field leveling is not necessary.
- Fields with irregular shapes are easily accommodated.
- Soil type plays a less important role in the frequency of irrigation.
- Soil erosion is lessened.
- Weed growth is lessened.
- Labour cost is less than other irrigation methods.
- Variation in supply can be regulated by regulating the valves and drippers.
- Fertigation can easily be included with minimal waste of fertilizers.
- Foliage remains dry, reducing the risk of disease.
- Usually operated at lower pressure than other types of pressurized irrigation, reducing energy costs.
How it works
Components used in SDI System (listed in order from water source) include:
- Pump or pressurized water source
- Water filter(s) or filtration systems: sand separator, Fertigation systems and chemigation equipment (optional)
- Backwash controller (Backflow prevention device)
- Pressure Control Valve (pressure regulator)
- Distribution lines (main larger diameter pipe, maybe secondary smaller, pipe fittings)
- Hand-operated, electronic, or hydraulic control valves and safety valves
- Smaller diameter polyethylene tube (often called “laterals”)
- Poly fittings and accessories (to make connections)
- Emitting devices at plants (emitter or dripper, micro spray head, inline dripper or inline drip tube)
Worth noting is that the layout of the pipes is done beneath the ground, the depth is dependent on tillage practices and type of crop to be irrigated.
In drip irrigation systems, pump and valves may be manually or automatically operated by a controller.
Because of the way the water is applied in an SDI system, traditional surface applications of timed-release fertilizer are sometimes ineffective, so SDI systems often mix liquid fertilizer with the irrigation water. This is called fertigation; fertigation and chemigation (application of pesticides and other chemicals to periodically clean out the system, such as chlorine or sulfuric acid) use chemical injectors such as diaphragm pumps, piston pumps, or aspirators. The chemicals may be added constantly whenever the system is irrigating or at intervals.
Factors the farmer needs to observe.
But like all good things, there are some factors the farmer needs to observe keenly to reap maximum returns from Subsurface Drip Irrigation.
Clogging: Since water is released through tiny pores on the plastic ducts, it is important for the farmer to constantly check the quality of water to ensure it does not contain suspended particles such as silt.
Bacterial slimes and algae growing on the interior walls of the laterals and emitters combined with clay particles in the water can block the emitters: To counter this it is important to ensure that the irrigation water does not contain the green algae and other slimes. Special care must therefore be taken when using water from open wells and reservoirs.
In case the farmer notices green algae or any biological slime in the water, use of chlorine would be used to clear the water.
If you are using salty water, you must also be aware of possible precipitation of salts, which can clog the tiny drip holes and render the system ineffective.