Carbon and nitrogen mineralization in tallgrass prairie and agricultural soil profiles

In situ mineralization of N mag contribute significantly to total inorganic-N pools deep in the soil profile. We conducted long-term laboratory incubation experiments to evaluate the net C and N mineralization in soils collected from various depths in tallgrass prairie and agricultural fields of the same geological materials and soil type. Samples were packed to a bulk density of 1.4 g cm(-3) in 5-cm-diameter by 10-cm-long cores. The cores were incubated at 35 degrees C for 40 wk in sealed containers. Net C mineralization was measured by evolved CO2, and N mineralized was measured by periodic leaching with NH4+ and NO3- measured in the leachate, Carbon and N mineralization in the surface horizon were greater in the tallgrass prairie than in the agricultural soil. In both the tallgrass prairie and agricultural soil profiles, C mineralization was least at the water-table depth, Carbon mineralization was described by a first-order kinetic model, but N mineralization was described better by a consecutive (sigmoidal) reaction model. At most depths, the ratios of potentially mineralizable organic C (C-0) to total organic C (C-0/TOC) and potentially mineralizable organic N (No) to total N (N-0/TN) were greater in the agricultural soil profile than in the tallgrass prairie soil profile, The C, and No in the surface soil (0-0.2 m) represented 11.6 and 12.2% of the total organic C and N pools fur the tallgrass prairie soil profile, respectively, and 21.0 and 10.2% of the total organic C and N pools fur the agricultural soil profile. Management practices affected the mineralization potentials and rates of both the surface and subsurface soils.