Long-term impact of topsoil depth and amendments on carbon and nitrogen budgets in the surface layer of an Alfisol in Central Ohio

The impacts of 20-yr using amendments on the restoration of properties of an Alfisol was evaluated at the Waterman Farm, Agricultural and Natural Resources Laboratory, Columbus, Ohio. The objectives of the experiment were to assess: (1) the effects of organic and inorganic amendments on soil aggregates, and (2) carbon (C) and nitrogen (N) budgets of soil removed (20 cm deep) and undisturbed plots after 20-yr was used to conduct the experiment. Five treatmentents were used in the rendomized block design viz; (1) permanent grass field, (2) soil artificially removed-N fertilizer added, (3) soil artificially removed-compost added, (4) an undisturbed (surface soil not removed)-N fertilizer added, and (5) an undisturbed surface soil-compost added. The experiment field was permanently under the no-till since last 20 yr. The surface soil removal plots amended with compost and permanent grass plots registered the lowest bulk density (ρb) of 1.37 and 1.38 Mg/m³, respectively. The highest concentration of sand (30.4%) was observed in the treatment with surface soil removed and compost added, while the highest silt content (48.0%) was obtained in permanent grass plots. However, the clay content was the highest (38.2%) in fertilizer amended undisturbed treatment. The higher proportion of macroaggregates (88.0 and 87.6%) and the mean weight diameter (MWD) (4.47 and 4.5 mm) were recorded in the undisturbed compost-amended and permanent grass plots, respectively compare to fertilizer applied plots. There were no differences in soil pH among sampling depths, but higher electrical conductivity (EC) was observed at 0–10 cm depth of fertilizer application, disturbed (174.23 µS/cm) and undisturbed (166.63 µS/cm) plots than 10–20 cm. The highest C:N ratio (11.0) was observed at the of 0–10 cm depth in artificaly soil removed organic compost-amended treatments. The highest rate of build-up of stocks was 793.3 Kg/ha for C and 50.5 kg/ha for N in 0–10 cm depth of undisturbed and compost-amended plots. Furthermore, the highest magnitude of the stabilization was 2.8 Mg/ha for C and 0.7 Mg/ha for N in surface soil removed and compost-amended treatment. The magnitude and rate of SOC accretion were 27.5 Mg C/ha and 2.0 Mg/ha.yr, respectively, under undisturbed and compost-amended treatment.