Climate change is bringing longer and more severe droughts and floods. Water supplies are limited in many areas and water costs are rising. Many families, communities and even countries are at risk. More efficient irrigation systems can make the most of limited water supplies. Over the last 40 years I have been testing and refining strategies for plant establishment in the Sonoran and Mojave deserts of North America with rainfall as low as 7.5 cm in a good year. Many of these systems can prove useful for home gardens, and growing shrubs and trees in arid lands.
My quest began back in the 1980s when I started searching around the world for low technology irrigation techniques suitable for arid sites. I also interviewed everyone who visited the Dry Lands Research Institute where I worked. I found out about several little known but very effective traditional systems that were in use, but not being studied by scientists because they were seen as primitive. In the years since then I have managed to test and refine most of these systems. What I have learned can benefit home and small market gardeners working in areas where water is increasingly costly or in short supply.
Irrigation demand is related to water needed for metabolic functions drawn from soil moisture in the root zone. Moisture stress in plants develops as a result of the interaction of limited rainfall, evaporation, wind, plant growth (transpiration), and air and soil temperatures. Low relative humidity (often <10%) and high desert wind speeds can lead to very rapid water losses from soils and plants. Many native plant species are adapted to drought once they get past the first few months or years. They may not grow, but they will hang on, waiting for the first big rain.
Shelters
Sheltering plants with plastic tree shelters, rocks, rock walls, sun shades, or dried plant materials can reduce plant water demand and improve survival and growth. Solid wall tree shelters might seem suicidal in very hot deserts, but in most cases they dramatically improved survival in my studies. With ground surface temperatures that may approach (70°C) and with wind and sandblast shelters can reduce stress and plant water demand. And often important, they reduce grazing by domestic and wild animals. The increased air temperatures in desert shelters have generally not been a problem but some species are more sensitive than others.
The key to minimizing water use is getting water to the root zone quickly and efficiently with no surface runoff, surface wetting and loss to evaporation. Moist soil can facilitate root extension and development of a large root system.
Rainwater Harvesting
Capturing and utilizing any rain that falls is also essential. This clean salt free water can help offset long term salt buildup from irrigation with high mineral content surface or well water. Surface shaping of microcatchments, swales, pitting, imprinting, and installing straw bundles vertically in holes or trenches can improve movement of surface water into the soil if significant rains occur. However, if precipitation is light the mulch may intercept much of the rain before it reaches the soil. Bath water and dishwashing water can be used in most systems if they are kept free of harmful materials. My parents used this water for their gardens for more than 30 years.
Drip systems are well developed, well studied, and work well in some cases, but they require regulated water pressure, careful filtration, and regular maintenance. Buried drip is often better, moving water deeper in the soil, but harder to monitor and repair. Drip emitters are easily blocked with sediment and salt and several insect species devote their lives to plugging the emitters. Many animals (including coyotes (wild dogs), rabbits, and other animals will chew on the tubing even when they don’t have water in them. I sometimes think that’s why it is often called spaghetti tubing. In one of my studies of animal repellents to protect young plants from grazing all the tubing was snipped while the plants were untouched. I should have put repellent on the drip tubing as well!
Irrigation systems you may never have heard of —but might consider
The following systems have worked well over many years of experience in a wide range of soil types and plant species. Most were discovered in traditional cultures around the world. All use much less water than the best conventional techniques and are suitable for both gardens, farms and reforestation. The best alternatives include:
1. Deep Pipe Irrigation
Deep pipe irrigation is a very effective yet little known irrigation method using an open vertical or near vertical pipe (plastic, conduit, bamboo with the web punched out, waxed cardboard tube, a bundle of sticks, a hole filled with pebbles or…) to deliver irrigation water to the root zone of shrubs and trees. I learned of this from contacts in India. Deep pipes are much more efficient than surface drip or conventional surface irrigation because they limit evaporation. My studies showed that plants developed a much larger root volume better adapted to survive if irrigation is interrupted or stopped. Plants started on deep pipes also grew faster after rare summer rains.
Deep pipe irrigation can be used with low quality water. It is possible to set up with simple materials and hand tools without extensive support systems (pressurized filtered water is not needed). The deep pipes provide better water use efficiency thanks to reduced evaporation. They also limit weed growth and competition. For hand watering a 4-5 cm diameter pipe is placed vertically in the soil 35-30 cm deep near the seedling. A few 3-5 mm holes should be spaced down one side of the pipe, and oriented to face the plant to facilitate early root growth. A cover is needed to keep out lizards and animals. This can be a rock or cap, but screen makes it easier to water. For a few pipes you can cut screens by hand, but for larger projects screens can be cut by a screen fabricator. They can be glued or wired to the pipes.
Deep pipes enable water to be applied quickly and efficiently to seedlings with no runoff even on steep slopes. This can be done by hand from a water jug or from a hose to a truck water tank. Placing the deep pipe on the upslope side of the plant protects it from slumping and burial. Pipes can be left in place or removed after a few seasons and reused. A new market has emerged with very nice but costly deep pipes.
Deep pipes are also be used with an intermittent flow drip or tube water delivery system. For me a 1.25 cm plastic pipe vertically placed pipe 25-50 cm deep worked with drip emitters placed in the pipe. This provides the benefits of buried drip systems, but is more easily maintained and repaired.
2. Olla (buried clay pot, pitcher) irrigation
The most efficient system of all uses a buried, unglazed terra cotta clay pot filled with water to provide a steady supply of water to plants growing nearby. This was first described 2000 years ago in a handbook written in China for people with too little land and too little water. Water seeps out through the walls of the buried pot at a rate that is in part determined by the water use by the plant. The controlled water delivery from buried clay pot irrigation provides plants with a steady water supply even during periods with very high temperatures, low humidity, and desiccating winds. The controlled water delivery is also helpful in coarse sand or gravel soils that drain too quickly and in salty soils. This steady moisture content in the soil also makes buried clay pot irrigation a good method for use with direct seeding and cuttings.
Buried clay pot irrigation allows soil amendments to be placed where they will benefit crop plants rather than weeds. In a study in Kenya clay pots cut water use 97% and increased yield 40% compared to surface irrigation. The precise water application also minimizes weed growth. A study in India showed that the dry weight of weeds in crops using buried clay pot irrigation was only 13% of the weed weight for controls using basin irrigation. In one of my studies weeds weighed only 23 kg/ha contrasted with 6,700 kg/ha for an adjacent surface irrigated plot.
Clay pot irrigation has worked well in areas affected by salinity or where only saline water is available for irrigation. In one study tomato yield was actually higher with slightly salty water. Clay pots are valuable for many problem sites in gardens, market farms, landscaping and revegetation. They work very well for plants that develop mold or rot easily if the leaves or stems get wetted. The buried clay pots can be filled by hand or connected to a pipe network or reservoir.
Buried clay pot irrigation is very effective for irrigating cuttings in the nursery or in the field. In the nursery a sealed clay pot is placed within a larger pot with the drain left open. The space between pots is filled with sand or a soil mix. The interior pot is filled with water and maintains moisture in the soil. The outer clay pot allows for good aeration and helps cool the container. Ideal for willows (Salix), cottonwoods (Populus), and some plants that are harder to grow from cuttings.
The primary disadvantage is the cost of commercial ollas in the US (GrowOya is an example). Local potters can provide comparable clay pots at much lower cost. This could be a new market for Jordanian potters. The pores of the pots clog over time with calcium and organic matter. They can be cleaned by scrubbing and soaking in water with vinegar added. Traditional users sometimes cleaned them by putting them back in the fire.
3. Porous clay pipe
Porous clay pipe works much like buried clay pots, but can have a few more weeds. The appropriate depth for burying the porous clay pipe depends on the properties of the clay pipe (clay content, organic material, firing temperature, firing duration) and the properties of the soil (texture, structure, density, porosity, soil organic matter), and the applied hydraulic pressure (if any). Porous clay pipe is buried in a level or slightly sloping trench at a depth of 20 to 40 cm for medium to fine-textured soils with rows of plants about 1 m apart. Porous clay pipes are often 10-15 cm in diameter with joints that fit together well and are sealed to prevent root entry and uneven water distribution. They are usually laid end to end with a watertight slip joint, cemented joint, or plastic or rubber connectors. Rubber connectors make it easier for the pipe system to be dismantled, cleaned, and moved.
Pipe placement in row crops has typically been done either directly under each row or between rows, but pipe grids have also been used. Because they wet a larger surface area than porous capsules or pitchers, the water delivery is less precise. The water is spread along a continuous horizontal band in the soil, and this is well suited to closely spaced row crops such as carrots and other vegetables. It has also worked well for apple orchards.
Porous clay pipe is demand-responsive with very high-water use efficiency. Experiments with buried clay pipes found that water consumption for turnip, okra, and eggplant using porous clay pipes was 80%, 81%, and 83% more water-use efficient than traditional flood irrigation. The crop yield also increased. Drawbacks include lack of suppliers, weight, effort to install challenge of cleaning.
4. Wick irrigation
One of the lesser known methods of irrigation uses a wick to conduct water to plants. I was first introduced to this very efficient form of irrigation in a paper from India, where wicks were used in conjunction with buried clay pot irrigation. Wicks can be either a gravity flow (fast) or capillary flow (slow) wick. Capillary flow occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules. This enables the water to rise up into the wick. Wick material must be tested, some materials are much better than others. Hang one end of the wick in colored water and measure the capillary rise. Water will rise in some wicks as much as 50 cm. For a gravity flow test simply lay out the wick and attach to the reservoir.
Solid braid nylon or polyester wick work best. Cotton can be used but is more likely to grow algae. A wick can be set up as a free flow system with only gravity pressure or as a capillary feed with water carried up and along a wick at very low rates for longer term watering from a reservoir. Wicks may prove useful for deep watering with minimal water use and high efficiency. A wick might help tie roots from the surface to to groundwater at 2-4 meters depth.
Much more needs to be done to develop better wick systems and to more fully evaluate the most appropriate uses of capillary and gravity fed wicks. The flow rate can be adjusted with a clamp on the wick just below the reservoir. A multiple wick arrangement could be used to develop a root pattern that would improve wind-firmness. Wicks could also be incorporated in a pressurized network. Wicks may also be very effective in establishing cuttings and in helping riparian plants reach groundwater. Wicks can also be used to water house plants when you must leave for a few days.
Which is best? It depends. Try them.
One of the advantages of these systems is their robust nature and low cost. Match irrigation to the need. I used to use deep pipes on many of my restoration projects. Today I rely on buried clay pots in my garden beds and for plants in landscape pots. They work so well!
Further reading
Bainbridge, D. A. 2023. Deep-root strategies for propagating and planting seedlings for arid sites. Tree Planter’s Notes. 66(1):87-92.
Bainbridge, D. A. 2021. Wick irrigation. Agroforestry Action Network. May. https://www.youtube.com/watch?v=zlsE4s0Fy90
Bainbridge, D. A. 2015. Gardening with Less Water. Storey Press/Hachette.
Bainbridge, D. A. 2006. Deep pipe irrigation. Overstory Agroforestry Journal #175. 6 p.
Bainbridge, D. A. 2001. Irrigation and surface mulch effects on transplant establishment. Native Plants Journal 2(1):25-29.
Bainbridge, D. A. 2001. Buried clay pot irrigation. Agricultural Water Management. 48(2):79-88.
Edwards. F. E., D. A. Bainbridge, T. Zink and M. F. Allen. 2000. Rainfall catchments improve survival of container transplants at Mojave Desert site. Restoration Ecology 18(2):100-103.
Bainbridge, D. A. 1996. Vertical mulch for soil improvement. Restoration and Management Notes 14(1):72.
Bainbridge, D. A., M. Fidelibus and R. F. MacAller. 1995. Techniques for plant establishment in arid ecosystems. Restoration and Management Notes 13(2):198-202.
Bainbridge, D. A. 1994. Tree shelters improve establishment on dry sites. Treeplanter’s Notes. Winter 45(1):13-16.
Bordas, J. and G. Mathieu. 1931. Résultats de deux années d’irrigation souterraine. Annales Agronomique. 1:186-194.
Kefa C. C., E. C. Kipkorir, J. Kwonyike, P. C. Kubowon, and H. K. Ndambiri. 2013. Comparison of water use savings and crop yields for clay pot and furrow irrigation methods in Lake Bogoria, Kenya. Journal of Natural Sciences Research. 3(8):34-39.
Lancaster, B. 2024. Turn scarcity into abundance. www.harvestingrainwater.com
Shi, S. H. 1974. On Fan Sheng-Chih Shu. Science Press, Beijing. Info on ollas in fragments of an ancient farm handbook 80BC.
Shiek’h, M. T. and B. H. Shah. 1983. Establishment of vegetation with pitcher irrigation. Pakistan Journal of Forestry. 33(2):75-81.
Siyal, A., A. A. E. Babiker and D. A. Bainbridge. 2024. Subsurface porous clay pipe irrigation: A sustainable solution for agriculture in Arid Regions. Academia Journal of Agricultural Research. DOI 10.15413/ajar.2024.101 (in press).
