Simulating change in soil organic carbon in two long term fertilizer experiments in India : with the RothC model

Abstract

Global importance of total organic carbon (TOC) in soil is due to its role in the global carbon cycle and, thus, the part it plays in influencing the atmospheric levels of greenhouse gases (GHGs). It is also of local importance as it determines ecosystem and agro-ecosystem function, influencing various soil parameters. The objective of the present study was to evaluate RothC model (26.3) to estimate TOC changes under two long term fertilizer experimental (LTFE) sites representing humid (Mohanpur) and semi-arid (Akola) climate in India. Five treatments each at the LTFE sites of Mohanpur representing alluvial soils (Alfisol) of the Indo-Gangetic Plains (IGP) and of Akola dominated by black soils (Vertisols) in the Black Soil Region (BSR) were selected. Mohanpur site was modelled for 3 layers (0-13, 13-23, and 23-39 cm) while Akola for surface layer (0-15 cm) only. The root mean square error (RMSE), considered as modelling error, ranged from 3.34 to 17.85%, 6.87 to 14.22% and 6.66 to 24.34% in the 3 soil layers of Mohanpur site respectively. For Akola, RMSE ranges from 1.79 to 13.28. The simulation biases expressed by M (relative error) for all treatments at these sites were non-significant. In Mohanpur, observed trends in TOC show marginal increase in control (T1) and 100% NPK (T2) while the increase was nearly 17 to 35% when organic amendments were applied along with inorganics during 1999 to 2010. For the same period in Akola, control (T1), 50% NPK (T2), and 100% NPK (T4) recorded decrease in TOC while 26 to 29% increase was registered without inorganics and with the combination of inorganics and organics respectively. The calculation of modelled TOC stock to find out effect of global warming indicated that treating the entire soil pedon as a homogenous unit will overestimate effects of global warming in accelerating decomposition of soil carbon.