Soil samples were collected from non-agricultural (forest and shrub lands) and agricultural lands (tea, rice paddy and upland) in Jiangxi Province, China and incubated at 60% water-holding capacity and 30℃. The results showed that the nitrification activity was weak or absent in the studied soils due to be acid (pH 4.2~6.3 with a mean of pH 4.9). The nitrification rate was significantly correlated with mineralization rate of organic N, but not with soil pH if NH₄⁺ was not amended into soils before incubation. In contrast, the nitrification rate was significantly correlated with soil pH if NH₄⁺ was amended into soils before incubation. For majority of the non-agricultural soils (14 of 18 samples), the nitrification rates were smaller than their net mineralization rate. Consequently inorganic N was dominated by ammonium rather than nitrate even after 56-days incubation. Nitrification activity was stimulated by agricultural use, dependent on land use types, with the greatest in upland soils followed by tea and paddy soils. Enhancement of soil pH by liming, application of N fertilizers, and improvement of available P status were the main factors stimulating nitrification activity in agricultural soils. The stimulation effect of agricultural use on nitrification weakens the capacity of humid subtropical soils to retain inorganic N. The NO₃^--N produced through nitrification may threaten the environment by leaching and run-off, particularly when N fertilizers are applied into agricultural soils in seasons with higher temperatures and heavy rainfall.