GROWTH OF THREE TIMBER TREES AS AFFECTED BY AMOUNTS OF WASTEWATER APPLICATION AND IRRIGATION SYSTEMS

Five-year-old Gmelina arborea, Khaya senegalensis and Tectona grandis seedlings were investigated at Sarabium Plantation, located in North Eastern Egypt, allocated for wastewater disposal. The study monitored the growth, above ground biomass, water use efficiency, nutrients and heavy metals content of these species throughout three seasons (2016, 2017 and 2018). The study was laid out on a randomized complete block design in split plot layout with three replications. There were 12 treatments including three irrigation treatments (A1) approximately 130 %; (A2) 100 %; and (A3) 70 % of evapotranspiration. These amounts of water was applied as main plot and four types of micro irrigation systems: bubblers (Bub.), on line dripper (Drip.), built-in dripper (G.R.) and sub-surface drip irrigation (SSD), as sub-plot factor. The results showed that using bubblers system together with the application of 10.3 l tree -1 day -1 of wastewater could be recommended in Sarabium area where water is not a limiting factor to provide the highest growth parameters and biomass production of Gmelina arborea, Khaya senegalensis and Tectona grandis tree species. Also, values of water use efficiency indicated that 0.76, 1.01, 1.33 and 2.4 m 3 of water were needed to produce one kilogram of dry matter yield using Bub., Drip., G.R., and SSD in Gmelina arborea; 0.59, 0.74, 0.97, and 2.0m 3 in Khaya senegalensis and 0.24, 0.40, 0.57, and 0.76 m 3 in Tectona grandis, respectively. This means that water savings were achieved with the Bub. system in comparing with Drip., G.R. and SSD were 0.25, 57, and 1.64 m 3 in Gmelina arborea; 0.15, 0.38, 1.41 m 3 in Khaya senegalensis and 0.16, 0.33 and 0.52 m 3 in Tectona grandis, respectively. The results of the present study could contribute in the Egyptian sustainable development strategy 2030, as it achieves the target of “managing the natural resources" through forestation the desert land and reuse the wastewater to produce woody biomass.