Some methods for improving water use efficiency
In much of the Third World, water is scarce during the dry
season, yet irrigated crop production requires tremendous quantities. Below are
some suggestions for helping farmers use water more efficiently. While each of
them will help conserve water, using several of these methods together will be
the most effective.
· Draw up a watering quantity
and frequency schedule tailored to the specific soil, weather, and crop.
Remember to consider the water supply and labor factors mentioned above. For
example, it might be possible to water older tomatoes just once very 4-5 days on
a clayey soil, yet the well may not be able to supply the large quantity needed
all at once.
Use the bed-and-alley system for small scale vegetable
production (see Chapter 4). By allowing much closer spacing of plants and
reducing soil compaction, it usually results in higher yields than using a
conventional wide-row spacing system. The higher plant populations and yields
per sq. meter of bed actually require little or no extra water, because the
closely-spaced plants shade the soil surface more effectively, thus acting as a
living mulch. Due to higher yields, water needs per kg of production are usually
Use windbreaks where hot, drying winds are a problem. They'll
cut down water losses from evapo-transpiration as well as protect from wind
damage itself. Staggered rows of fast-growing trees around the windward portion
of a garden can be very effective and also provide fruit, animal feed, and
firewood. (Refer to Chapter 3 for further details on windbreaks.)
Mulching the soil surface with peanut hulls, rice hulls, straw,
or dried grass will greatly reduce water evaporation losses. Mulching has
several other benefits (see Chapter 8) but may attract crickets, ants, termites,
slugs, and other harmful insects. Consider both preemergence and post-emergence
Choice of seedbed: Raised beds (if not mulched) dry out more
quickly than sunken or flat beds. Under very dry conditions, sunken beds are
usually the best choice, especially since they prevent water from running off.
(See Chapter 4 for seedbed styles).
Microcatchments are shallow "bowls" from about 30 cm to several
meters in diameter made in the soil with a plant or tree placed in the center.
They are very effective at collecting water from the surrounding area and
concentrating it around the roots. In rainy conditions, however, they may
promote poor drainage and encourage soil-borne diseases.
Various kinds of macrocatchments can be used which collect water
from larger areas that have moderate slopes. One technique is contour damming
where soil barriers are run across the slope to collect water runoff.
Soil conservation measures like contouring and terracing will
markedly improve water retention by lessening runoff from rainfall or watering.
See Chapter 3.
Rainwater can be collected off roofs and used for gardening.
Each sq. meter of roof will provide 1 liter of water per I mm of rainfall.
Good weed control will also reduce water losses, because weeds
can use up considerable amounts of water.
Where soils are very clayey and compacted, double-digging the
plots and adding organic matter to the subsoil will improve rooting depth and
allow greater intervals between watering. (See Chapter 4).
Adding compost or manure to sandy soils will increase their
Use partial shade on less heat tolerant crops like lettuce and
the Crucifer family (cabbage, broccoli, cauliflower, etc.).
The "double transplant" ("double nursery") method of raising
vegie transplants is worth trying. When transplants are big enough to be set in
the field, they are instead transplanted to a larger nursery seedbed where they
can be spaced about 15 cm apart. This allows them to be kept in a confined area
much longer, thus saving water as well as labor. This method works well with
tomatoes, since they have good tolerance to delayed field-setting. (They should
be "deep set" when transplanted so that most of the stem is buried underground
where it will generate new roots; most other vegies lack this ability.)
Choose drought-resistant varieties: This applies more to field
crops like maize where more work has been done on selection and breeding for
drought resistance. For example, even though maize isn't very drought tolerant,
there is considerable variation among varieties. However, choosing drought
tolerance at the expense of needed disease resistance or other desirable traits
may not be a good tradeoff.
Balanced fertilization, whether chemical or organic, helps
improve water use efficiency by stimulating more extensive root growth. Note,
however, that crops can't utilize as much fertilizer when moisture is limiting.
Soil nematode control: When present, root-feeding nematodes can
seriously inhibit water (and fertilizer) uptake by plant roots.
Drip irrigation is a method of supplying water to plants by
running small diameter plastic tubing down the row. Porous tubing (trickle
tubing) is used for closely-spaced crops like carrots; for crops wider-spaced
crops such as tomatoes, small individual emitters are used to concentrate the
water around the plants. Water is provided at low volume and pressure, and
plants are watered about once every day or two.
Drip irrigation can save water by delivering it close to the
plants and by reducing water runoff and the amount of wetted soil surface prone
to evaporation. However, water use efficiency is highest when the system is used
with widely-spaced plants like tomatoes and squash since less area needs to be
wetted. Orip irrigation is relatively inexpensive and, except for the
micro-tubing, most components can be fabricated from in-country materials.
Fertilizer can also be distributed through the system, though special soluble
types are needed. The main problem with drip irrigation is its tendency to clog,
even when fiItering is used. Improved tubing and emitter designs have overcome
this problem somewhat. With care, the microtubing may be used for several