Abstract:
Placing water beneath the soil surface via buried drip lines is slowly becoming the
preferred choice of many farmers. No doubt the use of subsurface drip irrigation
technology may well be the future of irrigation in the coming years and decades. It
holds the promise of reducing the weed growth, fertilizer and chemical use, labour
requirement and optimizing water use. Subsurface drip irrigation is an advanced and
recent revolutionary variation of drip irrigation. The aim of drip irrigation design is
to ensure uniform distribution of water to the crop with pre-determined application
of water. Therefore, for uniform outflow from emitter, information on their hydraulic
characteristics is very vital. The system is comparatively costly and prone to
clogging. It is therefore necessary to evaluate the performance in the field and see
whether their performance is meeting the design expectations. Hence the present
study was undertaken to analyze the hydraulics of subsurface inline drip irrigation
system, soil moisture distribution pattern, the effect of depth of installation of
laterals and levels of irrigation on growth and yield of ladies finger and to compare
the performance of surface and subsurface drip irrigation. In this study five depths of
installations (0, 5, 10, 15 and 20 cm) and three levels of irrigation were studied (1.0,
1.5 and 2.0 lit/ day/ plant).
The subsurface drip irrigation system was tested for their hydraulic
performance in the field at five depths of installations of 0, 5, 10, 15 and 20 cm in
terms of pressure-discharge relation, emission uniformity, manufacturing coefficient
of variation, friction factors, Reynolds number and application efficiency. The
discharge from emission points were collected at seven different operating pressures
ranging from 0.3 to 1.8 kg/cm 2. The power function was found to be good in
explaining the discharge exponent in deciding the flow regime. The discharge
exponent for the power function was found 0.7717, 0.7266, 0.5973, 0.5416 and
0.5325 for respectively 0, 5, 10, 15 and 20 cm which suggested an orifice type
turbulent flow emitter for the present inline dripper. The emission uniformity
values of the system were found to range between 74 and 94 % at different depthsof installation and varying pressure indicating average to excellent performance. The
manufacturing coefficient value (Cv) was found to be vary between 6.2 and 20 , as
the pressure varies from 0.3 to 1.8 kg/cm 2 . This indicated an average to marginal
performance of the inline dripper. The Reynolds number increased from 1460 to
6237 for the lateral pipe size of 16 mm with increase in inlet pressure from 0.3 to 1.8
kg/cm 2 and it also increased with increase in depth. This confirms that the turbulence
of flow increases with increase in pressure. The average values of friction factor
decreases from 0.0382 to 0.0365 for the same pressure of 1.5 kg/cm 2 as the depth
increases from 0 to 20 cm. It was also found that as the pressure increases the
friction factor decreases. The application efficiency increased with pressure and was
not much affected by depth of installation of laterals.
The soil moisture distribution pattern was found to follow a bulb shape in all
the contours. The maximum moisture content observed at the emitter position were
19, 24, 25, 22 and 22 % respectively for 0, 5, 10, 15 and 20 cm depths of installation
half an hour after irrigation. The maximum depletion was found at zero depth of
installation after 24 hrs of irrigation, while the same was considerably reduced in the
deeper installations. The best moisture distributions were observed at 10 and 15 cm
depths of installation after 24 hrs of irrigation.
A field study was conducted to study the effect of depth of installation and
levels of irrigation on growth and yield of ladies finger in sandy loam soil. The
highest fruit yield obtained was 8.1 t/ha for the treatment D 3 I 2 ie, the depth of
installation 10 cm and the level of irrigation 1.5 lit/day/plant. Water use efficiency
was found 11.24 kg/ha mm for the treatment D 3 I 2 . The analysis on biometric
observations also showed that the height, thickness and number of leaves of the
plant were found high at D 3 I 2. Hence the subsurface drip irrigation with 10 cm depth
of placement of laterals and 1.5 lit/day/plant of irrigation was considered as the best
treatment for okra in sandy loam soil. The maximum horizontal and vertical
movement of water front in the root zone of okra was found 37.5 cm and 52.5 cm
respectively. The moisture movement was observed to go beyond the maximumvertical and lateral spread of roots which indicated that the plant never had any
water stress during the crop period under subsurface drip. Therefore it is clear that
the adoption of subsurface drip technology should be enthusiastically pursued as an
appropriate technology to deal with increasing demand of water, environmental,
ecological and economic concerns