Provided is an iron-based powder for iron ion supply use, which achieves the improvement in the growth of a plant (crop) due to the dissolution of a bivalent iron ion and also achieves the increase in the yield of a crop produced by the aforementioned improvement.　In the iron-based powder, the total content of all of iron components is 60.00 to 98.00% by mass inclusive and the content of oxygen is more than 1.50% by mass and not more than 35.00% by mass.