Soil organic carbon pools and productivity relationships for a 34 year old rice-wheat-jute agroecosystem under different fertilizer treatments

Soil organic carbon (SOC) pools are important in maintaining soil productivity and influencing the CO2 loading into the atmosphere. An attempt is made here to investigate into the dynamics of pools of SOC viz., total organic carbon (C (tot)), oxidisable organic carbon (C (oc)) and its four different fractions such as very labile (C (frac 1)), labile (C (frac 2)), less labile (C (frac 3)) and non-labile (C (frac 4)), microbial biomass carbon (C (mic)), mineralizable carbon (C (min)), and particulate organic carbon (C (p)) in relation to crop productivity using a 34 year old rice (Oryza sativa L)-wheat (Triticum aestivum L)-jute (Corchorus olitorius L) cropping system with different management strategies (no fertilization, only N, NP, NPK and NPK+FYM) in the hot humid, subtropics of India. A fallow treatment was also included to compare the impact of cultivation vis-a-vis no cultivation. Cultivation over the years caused a net decrease, while balanced fertilization with NPK maintained the SOC pools at par with the fallow. Only 22% of the C applied as FYM was stabilized into SOC, while the rest got lost. Of the analysed pools, C (frac 1), C (mic), C (p) and C (min) were influenced most by the treatments imposed. Most of the labile pools were significantly correlated with each other and with the yield and sustainable yield index (SYI) of the studied system. Of them, C (frac1), C (min), C (mic) and C (p) explained higher per cent variability in the SYI and yield of the crops. Results suggest that because of low cost and ease of estimation and also for upkeeping environmental conditions, C (frac1) may be used as a good indicator for assessment of soil as to its crop productivity.