Long-term impact of manuring and fertilization on enrichment, stability and quality of organic carbon in Inceptisol under two potato-based cropping systems.

Soil organic matter (SOM) stability is a prerequisite for long-term C sequestration. The long-term effect of manuring and fertilization on stability of SOM in rice-potato-wheat (R-P-W) and maize-potato-onion (M-P-O) cropping systems was studied in an Inceptisol of semi-arid subtropical India. Soil samples were collected (0-15 and 15-30cm soil depths) from the following treatments: control, 100% NPK-Fertilizer, 100% N-Vermicompost (VC), 50% NPK-Fertilizer+50%N-Vermicompost (VC), 100%NPK-Fertilizer+crop residue (CR), 100% N-VC+CR. The stability of SOM was studied by correlating the ammonium oxalate extractable Fe, Al and Si with stable soil organic C (SOC). Application of 100% N-VC and 100% N-VC+CR increased the SOC stock by 66% and 32%, respectively over 100% NPK in R-P-W cropping system, while in M-P-O system, the above treatments increased the SOC stock by 28% and 12%. As compared to 100%NPK, the integrated use of 50%NPK+50%N-VC increased the SOC stock by 58% and 35% in R-P-W and M-P-O system, respectively. The extractable Fe, Al and Si significantly correlated with stable OC and the multiple regression model developed between these parameters could well predict the stable OC in soil. Complete or partial substitution of chemical fertilizer N with VC could be a promising nutrient management strategy for enhancing the SOC stock in Inceptisol under potato-based cropping systems of semi-arid sub-tropical India. However, the integrated use of 50%NPK+50%N-VC could be promising due to lowest yield reductions and moderate SOC sequestration potential. The enrichment (47%), as well as quality (81%) of SOC was higher in R-P-W system than in M-P-O system. The organic treatments like 100%NPK+CR and 100%N-VC+CR showed higher stability of SOC in R-P-W (31% and 26%) than in M-P-O cropping system. The stability of SOC could well be predicted by extractable amorphous and poorly crystalline Fe, Al and Si and SOC in both the cropping systems.