A pot experiment was conducted to study soil nitrogen(N) supply capacity in eroded and improved red soils.The eroded red soils were derived from Quaternary red clay and red sandstone.The improved red soils derived from Quaternary red clay had been applied with organic manure or inorganic fertilizers for more than 10 years.Results showed that the amount of soil N mineralized and supplied to plant in the soil derived from red sandstone was higher than in that derived from Quaternary red clay.Soil N supply capacity of the improved red soils increased significantly with the soil applied with organic manure taking the lead.When N fert ilizer was applied to eroded soils the N taken up by plant was low, with high N residue left in the Quaternary red clay in particular, and unaccounted-for N was low with a lower value in Quaternary red clay.When N fertilizer was applied to improved soils efficiency of N fertilizer was high.Both plant and soil recoveries in the improved soil applied with organic manure were higher than in that applied with inorganic fertilizers.