SUSTAINABLE WATER USE

This section is quite brief, consisting largely of a list of techniques that can be used to improve efficiency (and sustainability) of water use in agriculture. Recall that manyh of the problems we discussed relative to irrigation werre caused by system inefficiencies. For reminders on why water use in agriculture can be problematic, click on water limits or irrigation here. Some of the items listed below are not economically feasible for the farmer (if she/he wants to keep farming in their historical way), while others are quite reasonable.

• Use dripper systems rather than overhead irrigation. Dripper systems deliver water right to the plant roots, and can be oriented so that only the crop (rather than the rows between the crops) is irrigated. These are expensive, but very efficient, and are coming into wide use in some parts of the world, such as Australia, New Zealand, Israel, and portions of the US (including my own gardens at home!). Most use of these to-date is in high value vegetable and fruit production. (Some Israeli farmers are using a new generation of drippers, which are subsurface [buried 7 - 30 cm beneath the soil surface]. These are wonderful in many ways -- the surface of the the soil remains relatively dry, minimizing evaporative losses and germination of weed seeds; risk of soil salinization is diminished because little water is used; the system lasts longer than do surface-exposed systems; and labor costs are lowered, because there ins't a need to do seasonal installation and removal of drip system laterals, as there is with surface systems -- most mechanical operations can take place with the system in place below the surface. These systems are, however, costly.... [Science 25 Aug 06])
• Rather than using tall overhead sprinkler systems, where much water evaporates before it even reaches the ground, lower the water source and decrease the pressure of the application. For example, some low-energy precision application systems involve tubes that extend down to the crop from a sprinkler arm. These actually water plants better than many traditional systems (because of the lack of evaporative loss and the low-pressure, let-it-soak-in apect)so that yield increase. Increased yields coupled with decreased water costs can allow these sytems to pay for themselves within 2 - 7 years.
• Many irrigation systems are based on letting water run down furrows between the crop rows, using gravity. These systems can be very inefficient, as runoff off the low end of the furrow can be great and much water seeps through the soil without benefitting the crop. Growers can now obtain surge valves that increase the efficiency of water use tremendously (40% losses with traditional systems versus about 20% with surge systems). Rather than releasing water continuously, these release pulses of water. The initial pulses soak in at the top end of the furrow and essentially create a "seal" over that soil so that the water in subsequent pulses ends up moving more uniformly down the furrow to its end.
• Transport water in lined, covered canals rather than in unlined uncovered canals from which much water seeps or evaporates before reaching its destination.
• Irrigate at times other than the middle of the day, when much of the water evaporates as it is being applied or from the soil surface.
• Plant trees as shelter belts, which decrease not only wind erosion, but also, by decreasing winds, decrease evaporative and transpiration losses of water. These can decrease water losses to evaporation and transpiration by 13 - 20%. In addition, the trees sequester carbon!
• Water only when crops need it rather than on a fixed schedule.
• In relatively dry areas, raise crops that require less irrigation -- that is, match crops to real ecological nature of the land more closely. (For example, grow alfalfa, potatoes, wheat, and sorghum in dry areas, rather than water-hungry crops such as cotton or citrus.)
• Switch to dry land farming (= "rain fed" farming) -- lower production rates, but savings in water costs (and stored water, as in aquifers) may eventually compensate.
• Raise animals on relatively dry lands, instead of crops (assuming the land can take any pressure at all!).
• Simply quit farming areas that are too dry to sustain agriculture without irrigation.
• Charge more for water!! -- this may be particularly important as we face the prospect of global climate change, with consequent shifts in availability of water.
• Learn more about when, specifically, during the growing season crop water needs are greatest and when, in contrast, some water deficit can be tolerated without interfering with yields. In the N. China plain, some farmers using "deficit irrigation" can sustain their yields using 25% less water than before, because they have learned the critical stages during which crops must get sufficient water versus what stages can tolerate some deficit. In some cases there, farmers irrigate their wheat only three times per season instead of five, with similar yields (State of the World, 2004).

To move to the following section, on decreasing reliance on chemical pesticides in agriculture, click on ">>" below. To move to the table of contents for this unit on sustainable agriculture, click on sustainable here, and to return to the master table of contents for this BI 301 home page, click on "CONTENTS," below.

This page is maintained by Patricia Muir at Oregon State University. Page last updated Dec. 27, 2007.