The distribution pattern of fixed ammonium and maximum capacity of ammonium fixation in the profiles of several cultivated upland soils and paddy soils in Hunan province, China, and their influencing factors were studied with sampling on fields, and laboratory incubation and determination. The main results are summarized as follows： 1.The vertical change of fixed ammonium in profiles of the test soils varied with the soil types. There are 3 patterns in profiles of the paddy soils, i.e., fixed ammonium content increased with increasing depth in...
