Nowadays, much attention is paid to the increase in abiotic stress caused by climate change. Salt stress is one of the major limiting factors threatening the majority of plant species, such as Moringa tree.

This study aims to assess the optimum use of biochar to alleviate the salinity stress-induced effects on the germination and growth of Moringa oleifera. To achieve our objective, biochar was applied at 5, 10 and 15% rates and saline substrate was applied at several concentrations (5g, 10g, 15g/l NaCl). Our data showed that under the control condition (absence of salt), seed germination occurred earlier in soil amended with 5% of biochar compared to that in control soil (without biochar). It is crucial to note that the germination of Moringa seeds was reduced by 50% when the soils were amended with a rate of biochar of more than 10%. Moreover, in soil with increased salt stress levels, amendment with 10% of biochar enhanced germination. Furthermore, the leaflet number and seedling height were progressively reduced with the increase in the biochar amount in the soil. However, under th salt condition, 5% of biochar is efficient to alleviate the observed negative effect of salt on growth. In fact, the morphological aspects and growth of M. oleifera seedlings are diminished by biochar rates higher than 5%. It is demonstrated that salinity stimulated several adaptive responses such as antioxidant activity and a strong accumulation of secondary metabolites.

Concerning soil physical properties, regardless of culture condition, soil humidity is increased by the presence of biochar. Meanwhile, the soil's electric conductivity is reduced by the addition of a rate of 10% of biochar under control conditions.

We can suggest that biochar application at rate of 5% is recommended as an optimal level to enhance soil fertility, attenuate the negative effects of salt, stimulate germination and enhance the growth of Moringa oleifera under salt stress conditions.