Long term effects of topsoil depth and amendments on particulate and non particulate carbon fractions in a Miamian soil of Central Ohio

Abstract

Topsoil removal to incremental depths (TSD) under field conditions is a useful technique to simulate erosion, and assess its on-site impacts on soil properties and agronomic productivity. As the sustained productivity of the soils of US Cornbelt is threatened by topsoil loss due to erosion, the artificial soil removal and addition methods can help in assessing the on-site impact of soil erosion under natural field conditions. Thus this study was conducted in an Alfisol at Waterman Farm of The Ohio State University, Columbus, Ohio with the objective to assess the impact of long-term (13 years) effects of TSD treatments (removal of 20cm topsoil, undisturbed soil and addition of 20cm of top soil) with two amendments (organic manures and synthetic fertilizer) on particulate C fractions, and C associated with different size fractions. Application of organic or inorganic amendments to the eroded soil improved bulk density (BD) (1.57Mgm3), water stable aggregates (WSA) (87%) and mean weight diameter (MWD) (3.18mm) equivalent to undisturbed or soil addition treatments. However, the eroded soil had significantly lower total organic carbon (TOC) concentration (16.3gkg−1) compared to other treatments. A trend of higher TOC and nitrogen (TON) concentration was observed with manuring compared with the use of synthetic fertilizer. The lowest concentration (2.66gkg−1) of particulate organic carbon (POC) was measured in eroded soil, and it was 2.6 and 2.4 times lower than those of undisturbed and soil addition treatments, respectively. The sub-soil (15–30cm) accumulated significantly lower POC (3.6gkg−1) compared to the topsoil (0–15cm) (7.0gkg−1), with no difference among two amendments. The POC and N pools were also significantly lower in the eroded soil than in other treatments. The particulate organic C/N ratio was significantly larger in sub-soil (20.78) than surface soil (17.83), suggesting strong contribution of roots and root-derived products to POC. There was a positive correlation of macroaggregates C (>2mm and 0.25–2mm) with concentration of POC (0.58*, 0.41*) and PON (0.54**, 0.37*). The non particulate organic carbon (NPOC) pools increased with long term management, and were significantly correlated (R2=0.74**) with the TOC concentration. Higher stratification ratio for total and non particulate C and N was observed in undisturbed and soil addition treatments. Higher ratios (>2) of POC and PON in eroded treatments indicated the buildup of uncomplexed coarse organic residues of intermediate decomposition with higher turnover rate, and their positive impact on restoring the structural properties with the long-term use of amendments.