Nitrogen (N) dynamics in the agriculturally important alluvial soils of the southern Mississippi Delta are not well understood, and little information is available regarding the amounts of various forms of N present in these soils. Profiles of nine alluvial soils were selected to represent the principal agricultural acreage in the southern Mississippi Delta. Soils were sampled by horizon to a depth of 150 cm and the distribution of various N fractions were characterized. Forty‐one additional chemical, physical and mineralogical properties were measured, and regression techniques were used to determine if these soil properties were related to N distribution in the highly heterogeneous soils typical of this region. These profiles contained 11.6 to 26.5 Mt N/ha (average 18.8 Mt N/ha). The surface 15 cm contained an average of 4.8 Mt N/ha and accounted for about 26% of the profile N. Most of N in the surface 15 cm was recovered as organic N (78.4–87.4%), and the balance recovered primarily as nonexchangeable ("clay‐fixed") NH4+. In subsurface horizons, nonexchangeable NH4+represented a substantially larger fraction of total N (average 35.6 %). The amounts of exchangeable NH4+and NO3‐ were very low in most samples and accounted for only 0.2–0.7% of surface N and 0.3–2.5% (average 0.7%) of the total N accumulated within horizons. The proportion of total N recovered as organic N was most closely related to organic carbon (C) content and the amounts of 2: 1 type of clay minerals present in the horizon. Even though subsurface horizons contained an appreciable portion of their N as inorganic nonexchangeable NH4+, organic C content was the best single indicator of total N content (r2= 0.931) within the 52 horizons studied.