Field evaluation of fertigation uniformity as affected by injector type and manufacturing variability of emitters

Abstract

Fertigation with microirrigation systems is increasing in popularity. Uniformity of fertigation is important for many reasons. Field experiments were conducted to evaluate the effects of injector types and emitters on fertigation uniformity by simultaneously measuring the distributions of water application, solution concentration, and fertilizer applied within a subunit of microirrigation system. Three conventionally used injectors, a water-driven piston proportional pump, a venturi device, and a differential pressure tank, were evaluated with three different emitters. The results indicated that both manufacturing variability of emitters and injector types had a very significant effect on the uniformity of fertilizer applied, while the uniformity of water application was mainly dependent on emitter type. The uniformity of solution concentration was dependent on injection methods. Emitters having a higher manufacturer’s variation produced a more nonuniform distribution of water application and fertilizer applied. For a given emitter type, a differential pressure tank produced considerably higher coefficients of variation (Cv) for water application and fertilizer applied than a proportional pump or a venturi injector because a differential pressure tank released fertilizer in a decreasing rate with time. To obtain a uniform fertigation distribution, an injector that can inject fertilizers in a constant rate is recommended. The relationship between water application uniformity and fertigation uniformity for a microirrigation system was established for different injection methods. Cv for fertilizer applied was very close to water application Cv for a microirrigation system using a proportional pump or a venturi injector as an injection device. However, fertilizer Cv for a differential pressure tank was approximately double of the water application Cv. The injection method and injector performance should therefore be considered in the design of microirrigation systems.