Method and composition for improving plant growth

A method for improving plant growth consisting of delivering to a plant, roots of a plant, soil or substrate, or seeds of a plant simultaneously, sequentially or separately from each other, a combination of inactive yeast and/or yeast derivatives with an at least one nitrogen source, with the proviso that at least one nitrogen source excludes ammonium nitrate, wherein said combination of inactive yeast and/or yeast derivatives and said at least one nitrogen source causes a greater plant growth than delivering to the plant, roots of the plant, soil or substrate, or seeds of the plant simultaneously, sequentially or separately from each other, i) the at least one nitrogen source alone or ii) the inactive yeast and/or the yeast derivatives alone.