Field evaluation of fertigation uniformity for subsurface drip irrigation systems

Field experiments were conducted to evaluate the effects of injector types and lateral depths on fertigation uniformity of subsurface drip irrigation (SDI) systems by simultaneously measuring the distributions of water application, solution concentration, and fertilizer applied. Three conventionally used injectors, a differential pressure tank, a Venturi device and a water-driven piston proportional pump and three lateral depths of 0, 15, and 30 cm. were used in the experiment. The results indicate that injector type and lateral depth had an insignificant effect on emitter discharge and the uniformity of water applied, but the uniformity for fertilizer applied is mainly dependent on injector type. The uniformity for fertilizer applied of the differential pressure tank is lower than that of the Venturi device and the water-driven piston proportional pump. For a given lateral depth, the differential pressure tank generally produced a higher coefficient of variation (Cv) for fertilizer applied than that of the Venturi injector and the proportional pump. The regression analysis between fertilizer Cv and water application Cv was conducted for different injector types. The results indicate that the fertilizer applied Cv is very close to water application Cv for SDI system using a Venturi injector or a proportional pump as an injection device. However, fertilizer Cv for a differential pressure tank is about 40% greater than that for the water application Cv. The injection method and injector performance should therefore be considered in the design of microirrigation systems and the injector devices capable of releasing a constant fertilizer rate are recommended.