| Abstract: | Aggregation often provides physical protection and stabilisation of soil organic carbon (C). No tillage (NT) coupled with stubble retention (SR) and nitrogen (N) fertiliser application (90 N, 90 kg N ha−1 application) can help improve soil aggregation. However, information is lacking on the effect of long‐term NT, SR and N fertiliser (NT, SR + N) application on soil aggregation and C distribution in different aggregates in vertisols. We analysed the soil samples collected from 0‐ to 30‐cm depth from a long‐term (47 years) experiment for soil aggregation and aggregate‐associated C and N. This long‐term field experiment originally consisted of 12 treatments, having plot size of 61·9 × 6·4 m, and these plots were arranged in a randomised block design with four replications, covering an area of 1·9 ha. Soil organic C concentrations as well as stocks were significantly higher under the treatment of NT, SR + N only in 0–10 cm compared with other treatments such as conventional tillage, stubble burning + 0 N (no N application) and conventional tillage, SR + 0 N. Mineral‐associated organic C (MOC) of <0·053 mm was 5–12 times higher (r = 0·68, p < 0·05, n = 32) compared with particulate organic C (POC) (>0·053 mm) in the 0‐ to 30‐cm layer. We found that NT, SR + N treatment had a positive impact on soil aggregation, as measured by the mean weight diameter (MWD) through wet sieving procedure, but only in the top 0‐ to 10‐cm depth. MWD had significant positive correlation with water stable aggregates (r = 0·67, p < 0·05). Unlike MWD, water stable aggregates were not affected by tillage and stubble management. Large macroaggregates (>2 mm) had significantly higher organic C and N concentrations than small macroaggregates (0·25–2 mm) or microaggregates (0·053–0·25 mm). We also found that N application had a significant effect on MWD and soil organic C in vertisols. It is evident that better soil aggregation was recorded under NTSR90N could have a positive influence on soil C sequestration. Our results further highlight the importance of soil aggregation and aggregate‐associated C in relation to C sequestration. Copyright © 2016 John Wiley & Sons, Ltd. |
