It is a common way to apply NH₄⁺ and K⁺ together in farming.Effects of NH₄⁺ on movement and transformation of K⁺ in fertilizer microsites in red soil and Fluvo-aquic soil were studied through an incubation experiment using soil columns.The fertilizers used in the experiment were NH₄Cl and KCl.Compared with the treatment of application of K⁺ alone, the treatment of addition of NH₄⁺ did not show any effect on diffusion distance of fertilizer K but did increase the concentration of water-extractable K in fert ilizer microsites.In the soil close to the fertilizer placement site, the concentration of exchangeable K was decreased as a result of the addition of NH₄⁺, which was not so apparent in Fluvo aquic soil as in red soil.Besides, the addition of NH₄⁺ significantly decreased the concentration of nonexchangeble K in fertilizer microsites, suggesting that the addition of NH₄⁺ reduced K fixat ion in soil crystal lattices, thus increasing the risk of K leaching in the two soils.