Improving water uptake by trees planted on a clayey soil and irrigated with low-quality water by various management means: A numerical study

The yield of avocado trees planted on clayey soils decreases due to irrigation with treated-waste water (TWW). We hypothesized that the main cause for this yield reduction is the reduction in water uptake by the trees roots. The aim of this numerical study was to identify the main soil factors that control the reduction in water uptake by the trees roots, and to test various soil substrate-based and water-based management schemes design to counterweigh the water uptake reduction. The study relies on physically based, three-dimensional (3-D) simulations of flow and transport in variably saturated, spatially heterogeneous, flow domain, conducted for three successive years. The main findings of this study suggest that: (i) the long-term effect of irrigation with TWW on the response of the flow system is attribute to the salinity of the TWW, and not to its sodium adsorption ratio, SAR; (ii) with respect to improving water uptake by the trees' roots, the water-based scheme that alternates irrigation water quality between TWW and desalinized water, DSW, (ADW) performed better than the water-based scheme that uses fresh water only (FW). The soil substrate-based schemes, TUFp, that used trenches with highly coarse-textured soil material and pulse irrigations, and, particularly, SAop, that used trenches with finer soil texture, performed substantially better than the soil substrate-based scheme that used trenches with highly coarse-textured soil material only (TUF); (iii) with respect to minimizing solute leaching below the root zone, the water-based schemes, FW, and, particularly, ADW, performed substantially better than the soil substrate-based schemes.