Effect of operating pressures on microirrigation uniformity

The effect of operating pressure heads on water application uniformity in m icroirrigation submain units was evaluated. Research results show that wate r application uniformity either increases or slightly decreases as operatin g pressure head increases in a range when the emission exponent x less than or equal to 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 emitt er discharge in submain units can be considered as approximately linear for operating pressure heads in a small range (usually between the allowable m inimum and maximum operating pressures of the submain units). These results help to estimate the average emitter discharge rate easily in a submain un it for an increased or decreased operating pressure head when one is attemp ting to manage emitter discharge dynamically according to the requirements of crop root growth for different periods. Generally, a microirrigation sys tem designed to meet the desired uniformity of water application according to the allowable minimum operating pressure head would be better when x les s than or equal to 0.5 because water application uniformity increases as op erating pressure increases if emitter discharges are being managed dynamica lly. However, a microirrigation system designed to meet the required water application uniformity according to the allowable maximum operating pressur e head would be better when x > 0.5 because, in general, water application uniformity increases as operating pressure decreases.