EVALUATION OF SUBSURFACE DRIP IRRIGATION EMITTERS ON A SPLIT-ROOT CONTAINER-GROWN CITRUS ROOTSTOCK (CITRANGE CARRIZO)

Among irrigation systems, subsurface drip irrigation allows obtaining values of water use efficiency higher than 90%. However, when emitters are installed below the soil surface, root intrusion can represent the main cause of emitter occlusion. To prevent this phenomenon, manufacturers normally include herbicides in the plastic matrix of the emitters. Objectives of this paper were: i) to evaluate the effectiveness of alternative anti-root agents embedded in the same emitter model and ii) to identify their possible effects on the growth of a commonly adopted citrus rootstock (citrange ‘Carrizo’). Five different anti-root agents were tested in 8 lined trees, planted in split-root containers in which half volume was irrigated with a control emitter (C) including a physical barrier (PB) against root intrusion, while the other half with one emitter containing the anti-root agent. The following root growth inhibitors were examined: Copper (Cu), Cyanamide at two concentrations (CY1, CY2), and two different herbicides, Trifluralin (R1) and Preventol ® (R2). One year after transplanting the trees, new vegetation was measured in all the trees, whereas the root development and the flow rate-pressure head relationship Q(P) of the corresponding emitters were measured in 3 containers per treatment, after baring the roots and removing the emitters; the possible presence of roots inside the emitter flow paths was finally observed. Experiments evidenced similar tree growth among treatments and the absence of effects on root growth produced by the anti-root agents. It was observed that in the control, as well as in four emitter models containing anti-root agents, root intrusion occurred. The average lengths of roots inside the flow paths were 7.20, 6.55, 5.63, 5.80, 8.70 cm for CY1, CY2, C, Cu, and R1, respectively; only in treatment R2 there were no roots inside the emitters flow path. Roots intrusion affected the Q(P) relationships, causing the complete clogging of some of the emitters in C and CY1, with reductions of the average flow rates ranging between 2%(Cu) and 31% (CY1) and a substantial increase of the coefficient of variation.