Effect of operating pressures on microirrigation uniformity

The effect of operating pressure heads on water application uniformity in microirrigation submain units was evaluated. Research results show that water application uniformity either increases or slightly decreases as operating pressure head increases in a range when the emission exponent x ≤ 0.5 in most cases. The water application uniformity decreases as operating pressure head increases in a range when the emission exponent x > 0.5. The relationship between operating pressure head and average emitter discharge in submain units can be considered as approximately linear for operating pressure heads in a small range (usually between the allowable minimum and maximum operating pressures of the submain units). These results help to estimate the average emitter discharge rate easily in a submain unit for an increased or decreased operating pressure head when one is attempting to manage emitter discharge dynamically according to the requirements of crop root growth for different periods. Generally, a microirrigation system designed to meet the desired uniformity of water application according to the allowable minimum operating pressure head would be better when x ≤ 0.5 because water application uniformity increases as operating pressure increases if emitter discharges are being managed dynamically. However, a microirrigation system designed to meet the required water application uniformity according to the allowable maximum operating pressure head would be better when x > 0.5 because, in general, water application uniformity increases as operating pressure decreases. Received: 29 November 1999