Profile Distribution of Carbon Fractions Under Long-term Rice-wheat and Maize-wheat Production in Alfisols and Inceptisols of Northwest India.

The knowledge of profile distribution of soil organic carbon (SOC) in long-term agricultural systems could help to store atmospheric carbon in the soil. We investigated profile distribution of easily oxidisable Walkley-Black SOC pool (SOC_WB) under long-term rice-wheat (R-W) and maize-wheat (M-W) cropping systems under soils of different pedogenesis. The soil samples were collected from the characteristic genetic horizons and analysed for carbon fractions. The SOC_WB was the highest in soils under R-W systems in both Alfisols and Inceptisols. The SOC_WB stock in the deeper profile horizons under R-W system was significantly ( p < 0·05) higher than that under M-W system especially in Typic Hapludalfs. Long-term R-W system could store on average 3·55 Mg ha⁻¹ more SOC_WB than M-W system in the Ap horizon. The SOC_WB stock in the Ap horizon of all pedons was significantly ( p < 0·05) higher in Alfisols than that in Inceptisols. About 60-90% of the total profile SOC_WB stock was contributed by B-horizon because of its greater extent. Considering the whole profile, clay was negatively correlated with SOC fractions; however, the SOC fractions were closely related to each other. This study reveals that the distribution of SOC_WB is different in long-term R-W and M-W systems not only in surface but also in the deeper horizons and the magnitude of the variation is influenced by the specific pedogenic processes. This indicates the significance of profile SOC_WB stock instead of topsoil SOC_WB stock in quantifying carbon retention potential of the long-term management practices. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]