Microbial Biomass and Activity in Relation to Accessibility of Organic Carbon in Saline Soils of Coastal Agro-Ecosystem

In coastal agro-ecosystems, soil salinity follows a decreasing gradient from coastal margin towards inland and this variation of salinity influences carbon (C) dynamics and soil biology. Following this trend, an experiment was conducted to study the changes in soil microbial biomass and activities in relation to organic C accessibility along salinity gradient and under different rice based cropping systems in coastal saline soils of eastern India. Findings inferred reduced soil microbial biomass and activities with increase in soil salinity. On the other hand, preponderance of flocculating Ca2+ with increase in salinity resulted in higher soil aggregation, formation of greater number of soil micro-aggregates within macro-aggregates and subsequent increase in aggregate-associated C. Further, there was increase in soil organic C (SOC) content but decrease in labile C per unit SOC with increase in soil electrical conductivity. Along with salinity induced hyper-osmotic stress, this higher soil aggregation and relative reduction in labile organic C might be accountable for curbed microbial biomass and activities in these soils, by restricting the availability of C for soil micro-organisms. Slow decomposition of organic C under prolonged submergence resulted higher accumulation of stable organic C under rice–rice-fallow cropping system as compared to soils under other rice-based cropping systems. © 2016, The National Academy of Sciences, India.