Influence of ammonium on release and fixation of potassium in soils was studiaied with eight soils derived from basalt,loess sediment etc.The increasing in availability of potassium in the soils was little by adding various amounts of ammonium under condition of submergence or alternate wetting and drying,but after wetting NH₄⁺ can prevent new fixation of K released from soil through airdried,thus keeping availability of potassium in the soil.For soils with mrca and illite as dominent clay minerals,K extracted with 1 mol/L boiling HNO₃ from soil added wish NH₄⁺ is 33-75 μg K/g less than that from soil without adding NH₄⁺.It indicates that NH₄⁺ can efficiently make potassium be occluded in the ditrigonal hole of 2:1 minerals,and the potassium will release difficultly.fertilizer K fixed in soils without leaching with NH₄⁺ and Ca⁺⁺ is 3.3-37.4%.After Ca⁺⁺ leaching,it has no more change compared with soils without leaching,except very few soils.The capacity of K fixation is greatly decreased in soils with NH₄⁺ leaching,only about 4% of fertilizer K is fixed.NH₄⁺ fixed in soils may dicrease the fixation of K from fertilizer and increase K fertilizer efficiency,but often ca uld cause leaching loss of K.Effects of NH₄⁺ and Ca⁺⁺ on K fixation in soils depend on the compsition of clay minerals in soil.The sequence of applying NH₄⁺ and K⁺ significantly influences the fixation of fertilizer K in soil.After 7 days of applying NHS followed by applying K,the fixation percentage of added K is the least,being 4.7-17.8%,and it is the highest,being 14.9-30.5%,when K⁺ was added 7 days befoxe applying NH₄⁺.When K⁺ and NH₄⁺ are added simultaneously,it is intermediate,being 4.7-24.1%