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International Journal of Horticulture 2014, Vol.4, No.14, 1
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lowers the risk of water logging and nutrient losses
below the root zone (Pitts., 1993). Successful
exploitation of ground water resources by a crop
depends on several factors that include water table
depth, soil water retention and transmission properties,
evapotranspiration demand, and plant root system
(Chabot., 2002).
Unlike deep water table conditions, a shallow
groundwater table maintains elevated soil moistures in
the root zone (Chen and Hu, 2004). However, in the
presence of shallow groundwater, a crop will use
water from both stored soil water and the groundwater
provided the groundwater quality does not preclude
plant use. For a shallow unconfined aquifer, water can
move upward from the water table to relatively drier
soil surface layers through capillary rise driven by soil
matric potential gradients. Ground water table
contribution to root zone moisture and zone of
maximum uptake is related to groundwater table depth,
soil unsaturated hydraulic conductivity, atmospheric
demand, the rooting depth, zone of active root
combined with water availability, the soil hydraulic
head (Chabot., 2002). Other factors are rainfall,
irrigation, root water uptake, soil evaporation, water
table depth, soil water retention and transmission
properties, evapotranspiration demand (Chabot., 2002;
Yeh and Eltahir, 2005; Fan., 2007).
Where water resources from ground water tables are
potential contributors to crop water requirements,
irrigation can be reduced with no detrimental effect on
crop yield (Patel and Joshi, 1986; Ayars., 2006). It is
necessary to quantify the effect of reduced irrigation
in presence of shallow water tables on water and
nutrient use efficiency and water savings without
reductions in yields (Hurst., 2004). If upflow can
contribute up to 30% of crop water use
(evapotranspiration) in well watered crops such as
soybean and wheat, in irrigation scheduling, water
additions which ignore the potential contribution from
upflow from water tables will exacerbate the problem
of excessive leaching and thus recharge. In the tropics,
there is scanty information on the irrigation
requirements of crops grown on inland valley swamps
characterized by shallow and variable water table
depths.
Irrigation scheduling using concepts of soil water
availability, such as readily available or plant
available water is unlikely to be useful for systems
with shallow water tables (Hurst., 2004). In addition,
the concept of replenishing a soil water reservoir as it
becomes depleted might also not be able to be applied
to root zones where upflow is a significant component
in the water balance and depletion of stored soil water
is not evident. For example, for a soil under the
influence of water table at 1.5m, the upper half of the
root zone is extremely dry and water is unlikely to be
available to plants. While the lower half of the root
zone is close to saturation, the low root densities
within a dry upper half of the root zone may prevent
extraction of water enough to meet potential
transpiration rates (Hurst et al., 2004). Talsma (1963)
and Hurst. (2004) opined that near saturated hydraulic
conductivity is a better indicator of potential upflow
rates, with distances between the root zone and water
table that maintain potential transpiration rates
increasing with higher near saturated hydraulic
conductivities. Inland valley swamps/floodplains, are
characterized by variable and shallow water table
depths, its contribution via capillary rise (upflow),
constitutes significant component in the root zone
water balance and can supply important fraction of
crop water use (evapotranspiration).
Extensive land areas in Nigeria are characterized by
shallow water tables fed by steams and river courses
(inland flood plains) and hence seasonally flooded.
The contribution to of ground water table via capillary
rise to soil moisture storage and crop water use
(evapotranspiration) provides a unique opportunity for
dry season crop production in inland flood plains. The
relevance of the soil and water resources of inland
valley swamplands to the attainment of year round
production of crops especially vegetables and the
attainment of food and nutritional security cannot be
over emphasized. The agricultural potentials of
tropical inland valley swamps or flood plains (Fadama
ecosystem) can be harnessed via the effective
management of its soil and water resources. It is
imperative therefore, to develop management
guidelines for sustainable exploitation of soil and
water resources of inland valley swamps to meet year
round crop production and for the attainment of food
and nutritional security, improved agricultural
livelihoods and contributes to productive wetland
based farming. Low-cost technologies (low head
/bucket gravity drip irrigation system) for small holder
farmers are available (IWMI, 2002; FAO, 2005). It is