Hydraulic Performance of Differential Pressure Tanks for Fertigation

Abstract

Differential pressure tanks are a widely used injection device for fertigation in micro-irrigation systems, but guidelines for managing a fertigation system using such a device are lacking. Laboratory experiments were conducted to evaluate the effects of design and operation parameters on hydraulic performances of differential pressure tanks. Three tank volumes of 10, 30, and 65 L with respective injection orifice sizes of 10, 21.5, and 23.5 mm were tested. In the experiments, the quantities of fertilizer applied were varied from 2 to 26 kg. Injection rate and variation of fertilizer concentration released from a tank with time were measured at several pressure differential heads ranging from 0.05 to 0.30 MPa. For all experiments, potassium sulfate (K2SO4) was used as the fertilizer, and the electrical conductivity (EC) of the fertilizer solution was measured. EC was converted to concentration by an equation calibrated prior to each experiment. The results revealed that the injection flow rate increased with increasing injection orifice size. The injection flow rate and pressure differential relationship can be represented by a power function with a power value of 0.5. The released concentration from a tank depends on injection orifice size, tank volume, differential pressure head, and quantity of fertilizer applied, decreasing exponentially with time. It was found that the variation pattern of the released concentration was highly controlled by the injection orifice size and tank volume. Injection profiles can be altered by varying orifice size, tank volume, and differential pressure head. The information obtained from this study will be helpful for managing a fertigation system using a differential pressure tank as an injection device.