The invention relates to a non-toxic composition prepared from agricultural waste, which includes the steps of: a) hydrolysing the plant matter in acidic conditions； b) nitrating the released phenolic compounds； c) stimulating the coupling between the phenolic compounds which are nitrated or not； d) insolubilising and separating the coupled compounds； and e) drying the precipitated insoluble solids. The resulting composition has phytoregulating properties due to which the application thereof to plants induces favourable metabolic and physiological changes which promote increases in the mass of the roots and the exudate, in the foliar area and mass, in the photosynthetic capacity, in the resistance to biotic factors, in the tolerance to abiotic stress factors and/or in the productivity of the crops.
