This study aims to determine the characteristics of bottom ash from the gasification of four agricultural biomasses namely corn stalks and cobs, cotton stalks, and wood residues, for potential use as agricultural fertilizer. The methodological approach consisted in carrying out gasification trials for each of these biomasses under identical operating conditions on a pilot-scale gasifier. The fly ash was collected at the end of the tests from the reactor bottom and cyclone bottom for analysis. Analysis showed that the ash from the reactor bottom contained higher levels of mineral elements, including Ca, P, K, and Mg in comparison to the cyclone bottom ash. However, the latter exhibited a higher content of Zn. Trace metallic elements (TMEs) were present in relatively low proportions. Ash from the gasification of cotton stalks had the highest Ca, Mg, K, and P content. The TME content was relatively above the required threshold, but it remained below the threshold in the ash from corn stalks. This suggests that cotton stalk ash is more suitable for use in agriculture as a soil fertilizer.