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
many 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
- 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
- Raise animals on relatively dry lands,
instead of crops (assuming the land can take any pressure at
all!). Keep in mind, also, that raising of livestock uses a great deal of water.
- 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. The system of water allocation in the western US, "use it or lose it," should be re-evaluated in light of current and impending water shortages.
- 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). Deficit irrigation has also been shown to be successful with wheat, grapes, many fruit crops and some other crops, although it does not work well for every crop. Breed plants with higher water use efficiency and drought tolerance. This is generally difficult to accomplis while maitaining high yields, but has potential for some crops. Some varieties of rice, for example, require fewer days than others to mature their grain, which lessens their water needs. Breeders often go back to the old varieties of crop plants such as wheat or barley in a quest for those that have been selected for drought tolerance by farmers for hundreds of years; cross-breeding could incorporate the relevant genes into modern varieties. This is yet another example of the importance of retaining the wealth of genetic diversity that traditionally was found in the hundreds of crop varieties of the past.
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 Nov. 26, 2012.