Response of Swietenia mahagoni to some nutrients under salinity stress.

A pot experiment was conducted at the Nursery of the Experimental Station of the Horticultural Research Institute, Agriculture Research Center at Giza, Egypt, during the two growing successive seasons of 2017 and 2018. This work aimed to investigate the response of Swietenia mahagoni seedlings grown under irrigation water salinity stress to soil application of different concentrations of sulfur as well as foliar application of mono potassium phosphate (KH₂ PO₄) and foliar application of putrescine {NH₂ (CH₂)₄ NH₂ (1,4 diaminobutane or butanediamine)}. Survival percentage of S. mahagoni seedling was 100 % at salinity level of 4.69 dS m^-1. As salinity level increasing to 6.25 dS m^-1 survival % decreased to (64.30 and 69.60 %) in both seasons, respectively. All growth parameters, i.e. (height of plant, diameter of stem, number of leaves per plant, fresh and dry weight of leaves and roots, and length of root) decreased as the concentrations of saline water irrigation increased. Whereas, the highest values of free proline content, was gained by the highest concentration of saline water irrigation (9.38 dS m^-1). The most positive effect of combination treatments on height of plant, nitrogen percentage, and total chlorophyll in leaves were T₁₀ (putrescine at 300 mg/L) with salinity level of 4.69, dS m-1. However, the most positive effect of combination treatments on diameter of stem, number of leaves, fresh and dry weight of leaves and roots, and length of root were T₇ (monopotassium phosphate at 3g/L) with increasing salinity level to 4.69 dS m^-1, also, due to significantly increased phosphorus, and potassium percentage in leaves. It can be concluded that salinity level of 4.69 dS m-1 with putrescine at 300 mg/L or monopotassium phosphate at 3g/L were the best for improving vegetative growth, and chemical compositions of S. mahagoni seedling.