Water Resources Management - Practices of Irrigation and On-farm Water Management - page 154

Adopting efficient irrigation method : On-farm water use efficiency can be
improved by moving to a more efficient irrigation system. Sprinkler and drip
irrigation can save noneffective water loss. Minimization of water loss during
land preparation in wetland culture of rice (substitution by dry-seeded rice)
leads to lower total water requirement.
Deficit irrigation : Omitting irrigation at less sensitive growth stages of plants
(with respect to water deficit) minimizes irrigation requirement without sig-
nificant yield reduction. Research at ICARDA (Zhang and Oweis, 1999 ) has
shown that applying only 50% of full supplemental irrigation (SI) require-
ments causes a yield reduction of only 10-15%. Assuming that under limited
water resources only 50% of the full irrigation required by the farm would be
available (i.e., 4,440 m 3 for a 4 ha field), the deficit irrigation was compared
with other options by Zhang and Oweis ( 1999 ) . They showed that a farmer
having a 4 ha farm would on average produce 33% more grain from his farm
if he adopted deficit irrigation for the whole area, than if full irrigation was
applied to part of the area. The deficit irrigation increased the benefit by over
50% compared with that of farmers' usual practice of overirrigation.

In rice cultivation, instead of maintaining 3-5 cm ponded water, irrigating after
3-4 days of subsidence of ponded water (also termed as alternate wetting (ponding)
and drying (to saturation or field capacity)) leads to 20-30% water saving with-
out significant yield reduction. Deficit irrigation facilitates the use of applied and
stored (within root zone) water more efficiently, and increases WP (Ali et al., 2007 ) .
Other measures of increasing water productivity may also be practiced (Ali and
Talukder, 2008 ) .

Water Conservation Measures

Water conservation can be done by adopting the following principles:

• reducing evaporation

•

mulching

•

using super-absorbents

Reducing Evaporation

From Water Surfaces Evaporation from lakes, reservoirs, or other water surfaces
varies from about 2 m/yr for dry, hot climates to 1 m/yr or less for humid, cool
climates. In the 1950s and 1960s, considerable research was done to reduce evapo-
ration from open bodies of water by covering them with monomolecular layers of
hexadecanol or octodecanol. While evaporation reductions of about 60% have been
achieved under ideal conditions, actual reductions were much lower, and the use of
monomolecular films to reduce evaporation from free water surfaces has found no
practical application. Instead, more success has been obtained with floating objects
in small reservoirs. Floating sheets of foam rubber have been successfully used.
Evaporation reductions of close to 100% have been obtained with such covers.