Optimal Value Of Drip Irrigation Unifomrity And System Design

For the application of microirrigation technology, how to decrease the system cost, at the same time, without sacrificing water use efficiency has been a mostly concerned issue during the past several decades. Irrigation uniformity is one of the most important parameters in system design and field management. It directly affects the system initial investment and crop yield. Currently, determining of irrigation uniformity is lack of sufficient support form scientific research. Some studies used field experiments to explore the effects of irrigation uniformity on soil water, nitrogen and salt content and distribution, as well as crop yield under different climate condition. Data obtained shows that, current design criterion(Cu=0.8) is acceptable and can be lower to decrease system cost. Water redistribution in soil has the compensating effect to non-uniform irrigation. At the same time, the extension of root system can ease the negative effect from uneven distribution of soil water and nitrogen. Therefore, in order to convert the theoretical “lower space” to the realistic design criteria which is practical,we should understand the relationship between system, soil and crop. The optimal value of system uniformity should be determined based on economic analysis and highest economic efficiency, and should be varied according to different crop and climate condition. Then, this study takes irrigation uniformity as research objective. Using field experiments, numerical simulation and theoretical analysis as research method, a hydraulic analysis model was firstly established. The optimal value of microirrigation uniformity was proposed according to different crop with specific root characteristics. The relationship between system uniformity,soil water uniformity and crop yield was established to guarantee the effectiveness of the optimal system uniformity. Finally, some issues in system design was discussed. Some conclusions are as follows:(1) The finite element model can be effectively used in the hydraulic analysis of different microirrigation submain unit including looped and branched system. It can accurately simulate the pressure head, flow rate distribution, system uniformity and coefficient of flow variation. Local head loss was calculated by equivalent length and local loss coefficient method. The results are precise.(2) Evaluation of soil water distribution is related to the sample positon, sample number,test time and duration. The continuous data from TDR sensors can relatively effectivelyreflect the variation of soil water content and uniformity in the growing season. When lateral and emitter spacing decreases, soil water content uniformity increases and the distribution of nitrogen and salt tend to be even. The model proposed can evaluate the relationship between soil water content uniformity and system uniformity. Calculated results correlates well with experimental data.(3) Soil water uniformity affects root system directly and then alter the pattern of plant growth above the ground. In general, with the increase of soil water content uniformity, crop yield and water use efficiency increase. When uniformity changes between 0.80 and 0.94,although the variation of crop yield is significant, the overall trend is stable. When uniformity further decreases from 0.80 to 0.79, crop decreases dramatically. As to field crop with low root system, soil water content uniformity should be not be lower than 0.80.(4) As to a typical field crop cotton, the optimal value of system uniformity is 0.78. As to an orchard olive, the optimal value of system uniformity is 0.86.(5) The original finite element model was improved. The convergence time is greatly improved without losing accuracy. It can be used in system design. Looped submain unit is more reliable and flexible. In some certain circumstances, looped submain unit can provide higher uniformity with lower cost.