The exogenous organic and inorganic nitrogen transformation process and its distribution characteristics in soil aggregate were studied in a pot 15N labeling techniques under low and moderate fertility levels with different fertilizer in red soil.Results showed that soil nitrate nitrogen,microbial biomass carbon and nitrogen,and enzymatic activity were significantly increased with chemical and organic fertilizer combination,whatever improving nitrogen fertilizer residue and reducing the loss in low or moderate fertility red soil.The content of microbial biomass carbon,nitrogen and nitrate nitrogen in moderate fertility red soil was equivalent to 1.8,1.3,and 2.0 times of low fertility red soil in the whole growth period under the same nitrogen application treatment,respectively.Urea application had no significant effect on nitrate nitrogen content in moderate fertility red soil,but it was increased by 5.7 times in low fertility red soil.N fertilizer application could significantly improve aboveground nitrogen uptake of wheat in low fertility red soil,which were 2.1~3.3 times as control,but there were no significant differences among different nitrogen application treatments in moderate fertility red soil.Organic fertilizer could significantly increase exogenous nitrogen residue in soil aggregates,which was 2.1~5.0 times of single chemical fertilizer.Compared with single nitrogen fertilizer,organic nitrogen or inorganic nitrogen combined with manure was prior to entering into the macro aggregate,but the residue and distribution of exogenous nitrogen had no obvious difference in micro aggregate and silt and clay.This research indicates organic fertilizer or combined with inorganic fertilizer could effectively reduce nitrogen loss and improve the nitrogen preservation in soil,especially organic inorganic fertilizer combination could significantly promote the growth of follow crops for the moderate fertility soil.