Soil organic carbon pools and productivity in relation to nutrient management in a 20-year-old rice-berseem agroecosystem

Labile fractions of soil organic C (SOC) can respond rapidly to changes in C supply and are considered to be important indicators of soil quality. An attempt is made in this paper to investigate into the dynamics of total organic C (C (tot)), oxidisable organic C (C (oc)), very labile C (C (frac 1)), labile C (C (frac 2)), less labile C (C (frac 3)), non-labile C (C (frac 4)), microbial biomass C (C (mic)), mineralizable C (C (min)) and particulate organic C (C (p)) in relation to the system productivity of a 20-year-old rice (Oryza sativa L)-berseem (Trifolium alexandrium L) cropping system with different management strategies [no fertilization, only NPK and NPK+FYM (farmyard manure) applied in different seasons] in the hot humid, subtropics of India. Cultivation over the years caused a net decrease, while balanced fertilization with NPK maintained the SOC. About 62% of the C applied as FYM was stabilized into SOC. The passive pool (C (frac 3)+C (frac 4)) constituted about 55% of the C (tot). A larger proportion (63%) of applied C was stabilized in the passive pool of SOC. Of the analysed pools, C-frac 1, C-mic, C-p and C-min were influenced most by the treatments imposed and explained higher per cent variability in the yield of the crops.