Assessment of Carbon Pools and Stocks in an Inceptisol Under Long-Term Manuring and Fertilization in Rice-Wheat Cropping System: Comparison of Different Methods

The objective of the study was to assess the 32 years impact of long-term manuring and fertilization on soil organic C (SOC) pools and stocks under rice-wheat cropping system in an Inceptisol and compare different methods for estimation of labile and resistant SOC pools. The treatments included control (T1), 100% NPK- fertilizer (T2), 50% NPK + 50% N-FYM (T3), 75% NPK + 25% N-FYM (T4), 50% NPK + 50% N-wheat straw (WS) (T5), 75% NPK + 25% N-WS (T6), 50% NPK + 50% N-green manure (GM) (T7), and 75% NPK + 25% N-GM (T8). The soil samples were analyzed for SOC, oxidizable and resistant C by hot water (HWEC, HWRC), KMnO4 (KMnO4-Cox, KMnO4-Cres), NaOCl (NaOClox, NaOCl-Cres), bulk density. As compared to 100% NPK, the SOC stocks (0-60 cm) in T3, T5, and T7 were increased by 10, 9.3, and 5.6%, respectively. The mean NaOCl-Cox, C mineralization (Cmin), HWEC, and KMnO4-Cox stocks contributed 37, 11, 6, and 4% of SOC stock. The correlation study showed that Cmin positively correlated with KMnO4-Cox, HWEC, and NaOClox. For assessing the mineralizable SOC pool, NaOCl-Cox overestimated, while HWEC and KMnO4-Cox underestimated it. Thus, these protocols need to be modified to match the Cmin data. However, NaOClox is recommended for assessing mineralizable SOC over 90 days of incubation.