An automatic irrigator that does not require electricity and can be made with used materials. This rustic and efficient creation by an Embrapa researcher will help from smallholders to amateur gardeners keep their seedbeds automatically irrigated through the dripping method. Developed by the physicist Washington Luiz de Barros Melo, a researcher from Embrapa Instrumentation (São Carlos, SP, Brazil), the equipment is based on a simple principle of thermodynamics: air expands when it is warm. Melo relied on this property to use air as a pump that pushes the water for irrigation. A black-painted bottle made of rigid material is turned over another bottle that contains water. Once the sunlight slants through the dark bottle, the heat warms the air within, which expands and pushes the water from the bottom container through a thin hose to drip in plants. It works so well that if you shade the bottle, the dripping stops, and when the sunlight catches it again, the water drips back", states the researcher who presents his invention at the 67th Meeting of the Brazilian Society for the Progress of Science (SBPC), from July 12 to 18 at the Federal University of São Carlos (UFSCar), São Paulo. Two other water containers are part of the invention: an upside-down rigid bottle plays the role of a water tank to keep drip bottle supplied, and a larger container conected to the "water-tank bottle" that stores a larger volume of water that will be used in the whole the system (see the scheme below, adapted from the publication). The tubes that connect the bottles can be made from hospital drip lines, for instance, but I have already used even electric wire covering after removing the copper wires from within, and they worked too", the researcher reports. He explains that the biggest challenge for those who make the equipment at home is sealing it. For the system, it is necessary that the three first bottles are hermetically sealed. "This can be done with plastic adhesives, like those made by Araldite, but it requires careful application", he teaches. Another part of the system is the distributor that can be built from PET bottles, and from which the tubing that will perform the irrigation is placed. Economical and ecological There are several advantages in the homemade irrigator that Melo lists. It is an automatic system without photocells and that does not require electricity, as it only depends on sunlight, which makes its operation extremely economical. It also saves water, as it resorts to the drip irrigation method, which prevents waste. "Moreover, it is possible to build it from objects that would be thrown away, like bottles and plastic, metal or glass containers", the specialist highlights. The equipment is quite versatile as well. Drip intensity can be regulated through the drip height, and farmers can put nutrients or other inputs in the resevoir water to optimize irrigation. (1) primary container; (2) container (1) coupling funnel; (3) coupler for containers (1) and (4); (4) secondary container; (5) sucction duct; (6) valve; (7) feeder duct; (8) pressurizer or solar pump; (9) hot air escape tube; (10) coupler for containers (8) and (11); (11) exit container; (12) drip duct or double siphon; (13) siphon valve (11); (14) drops; (15) base. When the sun shines on the solar pump (8), the internal temperature rises. The air within expands and pushes through tube (9); air pressure over the liquid in container (11) has it pour through tubes (7) and (12). Water drips from tube (12). Container (11)'s internal pressure decreases. Then, the water from container (4) moves to container (11) to replace the water lost. But that generates a small vacuum in container (4). The vacuum causes suction of the water found in reservoir (1). Once there is no more light, the sun-powered pump (8) tends to cool, decreasing container (11)'s internal pressure, which creates a greater vacuum in container (4), and increases (1) reservoir water suction. This process continues until the volume of container (11) is completely filled. More information can be obtained through the link (publication in Portuguese). Translation: Mariana de Lima Medeiros