A primer on micro-irrigation technology

Micro-irrigation technologies provide access to water, water storage, and water distribution for small-scale plots (typically, less than one hectare). These technologies may seem simple, but often require specialized training and knowledge for success, including proper design, placement, and maintenance. Equipment also needs to be effectively integrated, sometimes incorporating other technologies (such as, ways to store vegetable produce), to be truly effective.

Water Access

Pumps are labor-saving and time-saving devices that can lift and move water from surface and subsurface sources such as rivers, lakes, and aquifers. Pumps can be operated manually or powered by a fuel source (i.e., diesel, electric grid, solar energy). The price typically depends on the level of complexity (i.e., the number of moving parts), the output volume (i.e., flow rate or the amount of water that can be moved per second), mass production, availability, and brand/reputation (i.e., perception of quality, availability of warranty).

iDE has long supported inexpensive manually-operated pumps as a solution for low-income farmers to replace water lifting by hand, selling more than two million treadle pumps over the last three decades. Many farmers who invested in a treadle pump in the 1980s were able to upgrade to petrolpumps. However, in recent years, the twin challenges of increased fuel costs (especially during the mid-2000s) and the contributing factor of fossil to climate change (especially small diesel engines) has led iDE to focus on the development of a solar-powered pump solutions for smallholder farms.

Manually-operated Pumps

Treadle pump. A foot-operated, low-cost option for accessing water where the depth to the water table is less than six or seven meters. Treadle pumps are often made of metal, but can be made more cost effective in some locations by using bamboo, eucalyptus, and/or other local materials for the frame and treadles. Treadle pumps can be fixed (mounted on a well casing and using the casing pipe as the pump support) or portable (using an inlet pipe that can be extended to surface water or down a well). A version that works by pressure is also available, but faces additional limitations due to the need to “prime” the pump, usually limiting water draw to half the normal capacity; the advantage is that a pressure treadle pump can lift water to higher elevations than the pump itself or for longer distances (up to 50 meters).

Hand-piston pump. A hand-operated, low-cost option for accessing water at greater depths (30-35 meters) than the treadle pump, the hand-piston pump uses a much smaller borehole. Because leg power is generally more powerful than arm power, more effort is required per unit of water, and irrigation using this pump tends to be limited to dense agriculture such as seedling nurseries.

Rope pump. A hand-operated, low-cost option for accessing water when the depth is out of reach of suction pumps (up to 35 meters). The pump uses a series of washers made of locally-available material tied some distance apart on a long loop of rope. This rope is threaded down into a well and back up through a pipe. Irrigation use tends to be up to 18 meters. Beyond that the pump is less efficient and more applicable to domestic uses that require less water. Since the water output is not pressurized, water has to be transported to the field or elevated for drip or sprinkler irrigation.

Engine Pumps

Solar pumps. Solar-powered pumps use small photovoltaic panels that convert sunlight to electricity to operate the pump. iDE has been instrumental in the development of two solar pump options:

The SF1 (previously known as the Sunflower pump) uses a 80 watt solar panel to lift water up to 10 meters with an estimated throughput of 1,600 liters/hour at 6 meter, or 2,500 liters/hour at 1 meter. The pump itself is surrounded by a metal guard to protect it and also has a USB port to charge small devices like cell phones. iDE tested the SF1 in real-life irrigation situations in Nepal, Honduras, and Zambia. The SF1 is manufactured and distributed by Futurepump, a social enterprise that iDE and the PRACTICA Foundation helped to establish.

The Sunlight pump can be configured with solar panels from 100-400 watt and can lift water up to 40 meters. A very compact design (length: 575 millimeters; width: 200 millimeters; height: 270 millimeters) and low weight (11.5 kilograms) provides portability. The Sunlight Pump is manufactured and distributed by Ennos AG, a Swiss social enterprise which was created as a spin-off from the Berne School of Applied Sciences. iDE tested early prototypes of the Sunlight pump in Nepal, Bangladesh, Honduras, and Ghana, and is testing the current Sunlight pump in Honduras and Nicaragua.

Internal combustion pumps. Small low-lift motorized pumps driven by small petrol or diesel engines with a typical capacity of 2 to 5 horsepower and a typical discharge of 2–15 liters/second have proved cost-effective for small farms. Prices for this kind of centrifugal pump have substantially decreased as the result of mass manufacturing in China and India, and is typically between US$200 and US$500, which more established small-scale farmers can afford and allows them to irrigate a substantial area of 1 to 5 hectares. The operational costs are mainly fuel costs, which are estimated at US$500/hectare per season.

Water Storage

Water storage for small scale irrigation serves two primary purposes. It provides water continuity where water supply is uncertain, and it can provide pressurized supply to irrigation systems. Water can be stored in-ground, such as in a reservoir, or above-ground, in bags or elevated tanks. Depending on the storage location, pumping or gravity is used to feed an irrigation line.

Header bags. Used to supply water to a drip irrigation system by suspending a large water-holding container (250 liters storage capacity) above field level. The higher they are suspended, the greater the pressure that will feed the drip system. Header bags were designed to replace more expensive buckets or tanks. They are also easier to store and ship, as they are made from a collapsible plastic exterior with an interior plastic liner. They also provide the ability to mix fertilizers with the water in the bag—applying nutrients and water to the soil with a greater uniformity and efficiency per plant.

Earth mound bags. Larger and flatter than header bags, these enclosed bags cover a larger area of ground, but also have to be sufficiently higher than the drip system to provide enough pressure to move water. Filling the bag requires a pressurized pump or for the non-pressure pump to be higher than the bag itself. CARE was inspired by iDE’s earth mound bag and developed a bag with Mexichem that is currently being distributed in the market.

Impluvium. An impluvium derives its name from the sunken part of an atrium in a Greek or Roman house that was designed to carry away the rainwater coming through a center opening in the roof. The modern Impluvium is a “closed” 2 meter high water tank that collects rainwater (23 cubic meters capacity) through a roof and gutter system. It uses metal sides to support an oversized plastic bag. The closed nature reduces evaporation and the large size enables the farmer to store large quantities of water that can be made available over a longer period of time. Initially designed in the iDE’s Technology Center in Burkina Faso with funding from SDC and the RAIN Foundation, the Impluvium concept was brought to Honduras where the design is being refined and adapted to context with support from SDC and Nuestra Cuenca as one of the technologies to enable rural families become more resilient to climate change.

Water Distribution

Drip irrigation

Low-cost drip irrigation uses plastic tubing that lays directly on the ground to direct water to specific locations. Drip systems offer a more efficient method of getting water to a plant’s roots when compared to traditional surface irrigation methods, with water savings from 30-70 percent when operated and maintained correctly. It also saves farmers valuable time and labor by reducing the amount of weeds that grow along with the crops in the fields. There is a wide range of drip irrigation manufactured, with variables for quality of plastic, type and amount of connectors, valves, filters, fittings, and line diameters.

Microtube. Narrow micro-tubes are inserted into soft flat water lines to bring water directly to the base of each plant. Not suited for closely spaced crops, such as wheat, rice, rape/canola, or similar, microtube irrigation is best used for high-value crops whose bases support a large network of fruit/produce, such as orchard trees, tomatoes, and row crops. Water pressure is required, and the larger the system, the more pressure is needed.

Pre-punched drip tape. Soft flat water lines are pre-punched (e.g., with 0.9 millimeter holes), at various spacing depending on different crop types. Water pressure is required, but typically a 0.75-3.00 meter header tank height is sufficient for gravity feed. Pre-punched drip tape is easier to install and costs less than similarly sized button, baffle, or microtube systems.

Button emitter. An optional add-on to pre-punched drip tape, button emitters direct a steady flow of water to a desired location. Inserting the emitters and ensuring they remain unblocked takes effort, but the addition offers many advantages to standard drip tape by being customizable to the farmer’s specific field conditions and layout. Compared to other options, button emitters are not as cost effective, but are extremely useful for specialized purposes (e.g., orchards).

Baffle pre-punched drip. A version of drip irrigation that utilizes small plastic sleeves, or baffles, that can localize water flow from pre-punched holes in water lines. Components are easier to repair and replace than button emitters, and the system can be rolled up and laid out for multiple crop cycles.

Sprinkler irrigation

Sprinkler irrigation uses water lines and pressure to outlets at multiple locations that spray water into the air to fall like rain onto a crop. Useful in locations where water scarcity prohibits flood irrigation but the farmer wants to grow crops for which drip systems are not feasible, such as closely spaced crops (e.g., wheat, rice). Because the entire field is wetted, higher weed growth occurs, as well as additional risk of fungal growth from wetted crop leaves.

Mini-sprinklers. Ideal for use with low-pressure pumps (i.e., manually powered pressure treadle pumps), the relatively low flow allows mini-sprinklers to be used in erosion-prone areas (such as slopes or other highly undulated fields).

Impact sprinklers. Powered by motorized pumps, low-pressure impact sprinklers have a high discharge with a greater throw diameter than mini-sprinklers at the same pressure head. They can be raised or used at higher pressure to cast a wider irrigation circle.

Other Technologies

Desert fridge. Using the physics of evaporative cooling, a desert fridge consists of two clay pots, one smaller than the other that can be placed inside the larger with the interstitial space filled by sand. Produce is placed in the inner pot, which is covered with a lid or damp cloth, and the water is poured into the interstitial area to wet the sand. Keeping the pots in a dry, well-ventilated space enables the moisture in the sand to evaporate, drawing heat away from the inner pot, and cooling its contents. The only maintenance required is the addition of more water, around twice a day.

Crop cooler. Designed by a partnership between Engineers Without Borders USA and iDE, the crop cooler utilizes piped groundwater that runs through pipes in a building’s walls to keep crops cool.

Fertilizer deep placement. An innovative technology that compresses high quality, nutritious chemical fertilizer into small pellets, to be placed in the ground alongside rice seeds. This ensures all the nutrients and goodness from the fertilizer goes straight into the roots of the plant, with none being wasted in the surrounding soil. This simple yet effective technology is proving to be hugely successful in helping subsistence farmers maximize their crop productivity and incomes. While not an irrigation technology per se, FDP is based on the same MIT concept of direct application.