Proper irrigation scheduling requires the knowledge of the soil-plant-atmosphere system, including the relationshipsexisting between its various components. During the last decade, the monitoring of soil water content(SWC) has been considered a standard way to determine when crops need to be irrigated. However, under dripirrigation systems in which laterals are laid on the soil surface or buried at a certain depth, the gradients of soilwater content are rather high and therefore the threshold of SWC below which crop water stress occurs shouldaccount for the position of the sensors; the threshold, in fact, depends on the specific crop system, as well as on therelative position of the measuring sensors with respect to the emitters. The knowledge of this threshold is crucialfor irrigation scheduling, especially when regulated deficit irrigation (RDI) strategies are planned during specificstages of crop growth. Objective of this work was to identify the threshold of SWC to be used for the preciseirrigation scheduling of a citrus orchard irrigated with a sub-surface system. To this aim, the soil water contentmeasured during irrigation season 2018 in the root zone depth and in two different treatments, were integratedwith the measurements of predawn and midday stem water potential and transpiration fluxes.The experiments were carried out in a commercial citrus orchard (C. reticulata cv. Tardivo di Ciaculli) located nearthe city of Palermo, Italy (38 4’ 53.4" N, 13 25’ 8.2" E), in which a subsurface drip system with twenty emittersper plant was installed at 30 cm depth. Each emitter discharged 2.3 l/h at pressure of 150 kPa. Experimental fieldwas divided in eight plots, half of which constantly maintained under full irrigation (FI) and the other half underdeficit irrigation (DI) during the phase II of fruit growth (from July 1 to August 20). The layout was equippedwith a standard weather station (Spectrum Technologies, Inc) and eight "drill & drop" sensors (Sentek, Stepney,Australia) installed in a central tree of each plot, 30 cm apart from one emitter; all the sensors were interfaced witha communications board that uses the cellular 3G data network to make an internet connection. The Scholanderchamber was used to measure predawn and midday stem water potential, whereas the Granier thermal dissipationprobes (two per tree) were installed in four trees to monitor sap flow.Experimental data evidenced that during the examined period transpiration fluxes in treatments DI resulted about75% of those measured in FI, due to the reduced irrigation volumes and the parallel reduction in vegetative growthobserved in the summer flush as a consequence of the lower pre-dawn water potential in DI (-1.1 MPa) comparedto FI (-0.4 MPa). Similar results were obtained when considering midday stem water potentials. Finally, thethresholds of SWC below which crop water stress occurs resulted, in the different plots, variable from about 0.20and 0.25 cm3/cm3.
|Number of pages||1|
|Journal||GEOPHYSICAL RESEARCH ABSTRACTS|
|Publication status||Published - 2019|