Maximum length of subsurface drip irrigation laterals subjected to backpressure.

To achieve a better SDI system design, the emitters' hydraulic characteristics and the flowrate uniformity along lateral lines under backpressure influence must be known. The objective of this study was to evaluate the effect of backpressure on the maximum length of irrigation laterals using two types of emitters (pressure-compensating and nonpressure-compensating) in different situations. Data from a field experiment combined with information obtained from a previously published paper was used, that tested driplines hydraulics behavior influenced by backpressure. The lateral dripline design technique based on statistical approach developed by Anyoji & Wu 1987 was used to calculate the maximum length. The variables that most influenced the maximum length of the laterals were the terrain slope and permissible flowrate variation. For nonpressure-compensating emitters, the maximum length of the irrigation laterals is up to 5% greater in subsurface applications than in surface applications. For pressure-compensating emitters operating under the influence of backpressure, there is an increase in the discharge exponent due to the small difference in flowrate between the surface and subsurface conditions, which also increases the influence of pressure variations on the flowrate thus, the surface laterals are up to 8% longer than the subsurface ones.