As water becomes more scarce and expensive, the popularity of drip irrigation has increased in Kenya. This rise in popularity has coincided with the development of new irrigation technology, combined with a smallholder farmers in Kenya to conserve water and cut on expenses.
In drip irrigation, water is delivered to individual plants at a low pressure and delivery rate to specific areas or zones in the farm. The slow application promotes a thorough penetration of the water to individual plant root zones and reduces potential runoff. The depth of water penetration depends on the length of time the system is allowed to operate and the texture of the soil.
Drip emitters apply the water directly to plant root zones and are very efficient and water-conserving by design. When applying water directly to the soil, there is virtually no waste from drift, evaporation or runoff. There are many designs of emitters available on the market, and even the mini- sprinkler, misters and mini-sprayer types are efficient in operation.
Drip systems are relatively easy to design, assemble and install, which is why they are popular in Kenya. Depending on landscape needs, design the system to connect to a main water line or connect it to a hose bib. These systems are easy to modify. In designing and assembling a drip system, advanced planning is critical to successful results. Reading, studying, observing drip systems and developing an overall concept of the installed principles of a basic drip system in Kenya are the places to start. From that point, draw a plan that includes the layout of lines, your choice of emitter, the flow in LPM (Litre per minute) of your water supply and the total number of emitters to install on each line or system. At this point, it is essential to develop your list of farm crops so that the system you design is matched to your actual needs. Understanding the soil characteristics and topography in your landscape or garden is another important factor. The size and spacing of emitters you choose are affected by the different ways sun, exposure (N, S, E, W) and water move through the various types of soils. Soil types include clay, silt, sand (fine, medium and large particles) and loam. The amount of organic matter available in the soil also affects the soil’s capacity to hold water. All drip irrigation systems used in Kenya have five major and two optional components, and understanding these is the next step in actually designing a system.
- Valves: hand operated or electrical, and capable of operating at low pressures and low delivery rates. Drip systems are usually designed for automated operation using timers or specially engineered low-flow solenoid valves. Installation of a pressure vacuum breaker (PVB) or anti-siphon valve is also a necessity when using a well or a municipal water source. This valve prevents fertilizers or chemicals used in the drip system from siphoning back into the water supply when changes in system pressure occur.
- Pressure regulators: spring or valve. Most drip systems operate on low pressures, with 20 to 30 psi offered as the standard operating pressure. These pressures are lower than those provided by municipal water supplies, which means a pressure reducing or flow control valve is a necessity for the system to operate properly. A call to your local water distributor will provide you with information on the available pressure of your water supply. Pressure regulators come in two types, spring (used on smaller systems) and diaphragm. These devices are inexpensive and reliable in holding pressure constant. Adjustable and pre-set types are available.
- Filters: disk, screen or sand. For smooth operation and prevention of clogging of the tiny outlets in the emitters, filters are considered an important component of the drip system. For wells or municipal water sources, use a screen filter (150-200 mesh screen) or disc filter. If you connect your system to any open or surface water sources, sand filters are an absolute requirement. Install these filters as a pair of sand-filled canisters, which are back-flushed to clean them.
- Blowout valve or automatic drain: Installation of these valves is a good maintenance practice to clean lines and prevent damage from freezing
- Water delivery system: polyvinyl chloride pipe (pvc); polyethylene tubing fitted with emitters, sprayer or line source drip tubing. The water delivery system is simply the network of tubing and water application devices that takes the water from the source and releases it at the destination.
- Automated controller– simple electric clock or computer.
By automating your system, it is very convenient to maintain an irrigation schedule. Watering can take place in the wee hours of the morning or when people are away from home. Electric solenoid valves are used to automate the system with the addition of a time clock or automatic controller box (computerized controller). Buy a controller that allows (90 to 120 minute) settings and multiple start times.
- Fertigation system– electric and hydraulic pumps, cartridge systems, “hozon” venturi systems, etc.
Drip irrigation systems have an option to apply soluble fertilizers in the irrigation water. Fertigation with nitrogen, a highly soluble nutrient that moves easily through the soil profile to plant roots, is the most common method. Fertilizer cartridges (100% water soluble), which dissolve and are distributed through the watering process, are one option.
Another reliable method involves a simple “hozon” venturi injector, which siphons soluble fertilizer from a bucket or container into the irrigation tubing.
Hozons are only suitable for plantings of ½ acre or less. In connecting a fertigation system, remember to place the fertilizer injections in front of the filter to screen any contaminants. A reduced-pressure vacuum breaker is sometimes required with the use of an injector system.
As you design your drip system, the components and options you choose will depend on your individual needs. They include the size of the system, the water source, the plants you want to irrigate and the degree of sophistication you desire.