Abstract:Low N use efficiency and high environmental risk of chemical N fertilizer are worldwide concern, which may be overcome by using new slow-release fertilizers. Purpose of this research was offering basic data for the production of humic acid slow-release fertilizers. The effects of NH4+ concentration, equilibrium time and pH value on the NH4+ (adsorption) of humic acid extracted from Shanxi brown coal and its absorptive regularity were studied by ion-exchange (equilibrium) method in this paper. The characteristics of isothermal adsorption and kinetics adsorption on humic acid was discussed too. Results showed that with the increase of NH4+ concentration, adsorption capacity of NH4+ increased. The (adsorption) of NH4+ on humic acid could be well described by Freundlich equation and its kinetics adsorption fit Elovich (equations) best. Under the condition of pH lower than 7.04, pH increase of medium was of great advantage of NH4+ adsorption and could improve the velocity of adsorption reaction. Under the condition of pH lower than 4.03, physical adsorption was the dominant. However, under the condition of 4.03