Tillage and drainage impact on soil quality - I. Aggregate stability, carbon and nitrogen pools

Effects of two tillage treatments, tillage (T) with chisel plough and no-till (NT), were studied under un-drained and drained soil conditions. Soil physical properties measured were bulk density (P-b), total porosity (f(t)), water stable aggregates (WSA), geometric mean diameter (GMD), mean weight diameter (MWD), organic carbon (OC) and total N concentrations in different aggregate size fractions, and total OC and N pools. The experiment was established in 1994 on a poorly drained Crosby silt loam soil (fine mixed, mesic, Aeric Ochraqualf) near Columbus, Ohio. In 2007, soil samples were collected (0-10, 10-20, and 20-30 cm) from all treatments and separated into six aggregate size classes for assessing proportions of macro (5-8, 2-5, 1-2, 0.5-1, 0.25-0.5) and micro (0.25 mm) aggregates by wet sieving. Tillage treatments significantly (P <= 0.05) influenced WSA, MWD, and GMD. Higher total WSA (78.53 vs. 58.27%), GMD (0.99 vs. 0.68 mm), and MWD (2.23 vs. 0.99 mm) were observed for 0-10 cm depth for NT than T treatments. Relative proportion of macro-aggregates (>0.25-mm) was also more in NT than T treatment for un-drained plots. Conversely, micro-aggregates (<0.25-mm) were more in T plots for both drained and un-drained treatments. The WSA, MWD and GMD decreased with increase in soil depth. The OC concentration was significantly higher (P <= 0.05) in NT for un-drained (P <= 0.01) treatment for all soil depths. Within macro-aggregates, the maximum OC concentrations of 1.91 and 1.75 g kg(-1) in 1-2 mm size fraction were observed in NT for un-drained and drained treatments, respectively. Tillage treatments significantly (P < 0.01) affected bulk density (P-b), and total porosity (f(t)) for all soil depths. whereas tillage x drainage interaction was significant (P < 0.01) for 10-20 and 20-30 cm depths. Soil P-b was negatively correlated (r = -0.47; n = 12) with OC concentration. Tillage treatments significantly affected (P <= 0.05) OC pools at 10-20 cm depth; whereas drainage, and tillage x drainage significantly (P <= 0.05) influenced OC pools for 0-10 cm soil layer. The OC pool in 0-10 cm layer was 31.8 Mg ha(-1) for NT compared with 25.9 Mg kg(-1) for T for un-drained treatment. In comparison, the OC pool was 23.1 Mg ha(-1) for NT compared with 25.2 Mg ha(-1) for T for the drained plots. In general, the OC pool was higher in NT system, coupled with un-drained treatment than in drained T plots. The data indicate the importance of NT in improving the OC pool. (C) 2008 Elsevier B.V. All rights reserved.