Investigation of Optimal Hydraulic Parameters of Surface - Drip Emitters for Row Crops in Various Soils

Abstract

Water shortage is forcing engineers, policy makers, managers and farmers to explore water efficient irrigation techniques. Sprinkler and drip irrigation methods are gaining importance day by day. Drip irrigation is considered comparatively more efficient than the sprinkler one. Supply and Services Companies design the drip system according to the material imported and available in their inventories. The designed efficiency of system is not achieved as required according to international standards. However, parameters of drip irrigation for its high performance and optimal working need to be studied thoroughly. Wetting pattern of soil under drip emitter is one of the most important parameters affecting the efficiency of the drip irrigation system. In this thesis field tests and standard sand box model experiments were executed to investigate the wetting pattern of various soils under different emitter-discharges. The tests in both the cases of field and sand-box-model were performed on four types of soils including sandy loam, loam, clayey loam and clay for emitter discharges of 1, 2, 3 and 4 lph. Equal volume of water was supplied in each experiment. Thirty two experiments were conducted both in field and sand box model to investigate the wetting pattern. The wetted diameter and depth of soil for an emitter were monitored in the field and in the sand box model. The wetted radii were measured in every experiment both on surface of soil and at some depth below surface where wetted radius was maximum. Finally, the maximum wetted depth and maximum wetted diameter were recorded at the end of each experiment. The volume of wetted soil was estimated using the measured data. The soil samples were collected and tested in the laboratory. The percentage of moisture in soil samples was recorded by gravimetric method in laboratory. The optimal emitter discharge and spacing for an efficient drip-irrigation system were obtained. The emitter discharge of 4 lph was found to be optimal for sandy-loam whereas 3 lph produced optimal results for the other three types of soil. Field experiments were conducted on evaluation of drip irrigation systems to compare optimally designed drip irrigation with that used conventionally in Potohar Regions of Pakistan. The crop yield, water productivity, economic water productivity and benefit cost ratio were used for comparison of various drip irrigation systems for cucumber crop. It was found that well designed drip irrigation system improved the yields in the range of 4.0 to 46.66 % over conventionally used drip systems. The average water productivity was 14% higher under well designed drip irrigation having its value as 29.46 kg/m3 for cucumber as compared to other systems having water productivity of about 25.10 kg/m3. Economic analysis shows that the average benefit- cost ratio of optimally designed drip irrigated cucumber crop was about 2.64 which is higher as compared to other systems of drip irrigation. It was observed that crop yield increases by 20-90 % and there was water saving by 50% if optimally designed drip system is used instead of other methods of irrigation commonly used in Pakistan. ii Emission uniformity 􀀁􀀂is another most common design parameter for trickle irrigation system. The uniformity of water application was investigated in this thesis by estimating uniformity coefficient and coefficient of variation. The parameters used to measure emitter discharge uniformity were, emitter flow rate variation, ratio of maximum to minimum discharge, ratio of minimum discharge to average discharge, coefficient of variation, uniformity coefficient and distribution uniformity. Five types of emitter systems used in Pakistan were studied. Finally, the empirical equations were developed to determine the maximum wetted radius and depth on the basis of different parameters including emitter discharge, irrigation time, bulk density of soil, hydraulic conductivity, initial and final soil-moisture-contents and percentage of sand, silt and clay in soil formation. Subsequently additional data was obtained (for sandy loam and clayey loam) by varying emitter discharge over a broader range (1.0 to 30.0lph) to improve the effectiveness of equations. Values of the empirical parameters of the equations were determined using hit and trial and generalized reduced gradient non-linear optimization technique. The developed equations using generalized reduced gradient non-linear optimization technique performed better than other methods and produced reasonable accuracy in predicting the wetted radius and depth (Nash and Sutcliffe coefficient up to 99%).The equations can be useful to predict data for design of an efficient drip irrigation system in absence of resources to perform experiments.