Dynamics and temperature sensitivity of soil organic carbon mineralization under medium-term conservation agriculture as affected by residue and nitrogen management options

In the scenario of global climate change, the enhancement and stabilization of soil organic carbon holds prime importance. In this context, conservation agriculture (CA) based practices i.e., diversified cropping systems and permanent bed (PB) holds great potential. In this article, we have compared the dynamics of soil organic carbon under mustard and wheat based systems [MMuMb, maize-mustard-mungbean and MWMb, maize-wheat-mungbean)] planted on PB, with and without residue (PB + R and PB - R) along with four nitrogen (N) management options [Un-fertilized, N through prilled urea (PU), N through sulphur coated urea (SCU), and N through neem coated urea (NCU)]. After 5-years of experimentation, to assess the medium-term impact of full CA (PB + R) in comparison to partial CA (PB-R) on SOC dynamics under mustard and wheat based systems with diverse N sources, we had conducted an incubation study at three temperature levels (27, 32 and 37 degrees C) in a sandy loam soil (Typic Haplustept) of north-western Indo-Gangetic Plains (IGP) of India. Wheat-based cropping system (MWMb) resulted in higher values of less labile, non-labile as well as total SOC, as compared with mustard-based system (MMuMb). On the other hand, MMuMb registered higher amount of very labile and labile SOC, with enhanced decay rate. The cumulative C mineralization (Ct) was 11-17% higher under MMuMb compared with MWMb, from all the soil depths at 27 degrees C. Retention of crop residue in PB increased total SOC by 11.5 to 19.5% compared with PB-R, across the soil depths. The Ct were significantly higher under full CA plots with lower decay rate (Kc), as compared to plots under partial CA. Application of N fertilizers registered a significant hike in total SOC compared to un-fertilized control plots. At the same time, the coated N sources i.e., SCU and NCU failed to cause any significant improvements in total SOC as compared with uncoated PU plots. On the other hand, coated urea treated plots registered significantly higher C mineralization compared with uncoated PU plots. Between the two coated urea products, the NCU application registered significantly higher C mineralization compared with SCU across the sampling events and temperature regimes from all the soils layers. Cropping system or residue addition/removal did not affect temperature sensitivity of SOC mineralisation. At the same time, addition of N-fertilizers, irrespective of sources lowered the Q(10) compared with no-N fertilization.