MTech.

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/cm2. 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 depths of 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/cm2. 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/cm2 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/cm2 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 D3I2 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 D3I2. The analysis on biometric observations also showed that the height, thickness and number of leaves of the plant were found high at D3I2. 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 maximum vertical 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