Abstract: In order to investigate transformation of diammonium phosphate (DAP) and vertical diffusion of fertilizer-P in acidic soils,a red soil column from Jiangxi,China was applied with DAP and incubated and then slices of the column were sampled for analysis. Results show that after 31 days of incubation,fertilizer-P diffused no more than 5 cm. Fractionation of amorphous inorganic P revealed that only a limited portion of the added fertilizer-P remained water-soluble. A major portion of the added fertilizer-P was transformed into Al-P,which is high in availability,and Fe-P,and a small portion into occluded P (O-P) . The various forms of P decreased in concentration along with the increase in distance from the fertilizer application site. DAP significantly raised soil pH,and drastically enhanced activity of soil Fe,and Al. As a result,the Fe3+ and Al3+ released from decomposition of insoluble soil minerals played a pivotal role on fertilizer-P fixation in acidic red soil.