Management of rice production systems to increase productivity

3.1.3. Water Management
Water control is the most important management practice that
determines the efficacy of all other production inputs (nutrient, herbicide,
pesticide, farm machines, etc.) in lowland rice farming. Poor soil drainage is
highly damaging to crops and, in the long run, degrades soils with the
eventual development of salinity and alkalinity (Balasubramanian, 1999). In
an irrigation system of 1,200 ha, with 2 crops per year in the Kou valley of
Burkina Faso, mean rice yields declined from 6.7 t/ha in 1970 to 4 t/ha in 1994,
mainly due to poor water control and crop management (FAO, 1994). In the
Gambian Jahaly Pacharr Project, identical constraints caused yields to fall
from their 1979 record high of 10 t/ha to recent 4 t/ha yield average maximum
yield, even with high fertilizer inputs. Farmers tend to flood their fields with
excess water whenever they get the opportunity to do so, because they believe
that rice does better under flooded conditions. Rice grown under traditional
practices requires approximately 700‐1,500 mm of water, 60‐80% of which is
required from transplanting to maturity to meet the evapotranspiration
demand and unavoidable seepage and percolation in maintaining a saturated
root zone (Guerra et al. 1998).
In lowland rice production, water is not considered an integral part of
the production cost by farmers and irrigation engineers in most of Africa.
Although there are water charges in most rice irrigation projects, this applies
only to the mechanical system delivering the water. When irrigation is by
gravitational flow from rivers and other water bodies, then these charges are
not applicable. However, when water becomes limiting farmers will consider
water saving strategies in order to produce a good rice crop, but when water
is in abundance, water saving strategies are almost never enforced.
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