Labile soil organic matter pools in a calciorthent after 18 years of afforestation by different plantations

Labile soil organic matter pools (LSOMs) are the fine indicators of soil quality which are influenced by changes in management practices. The suitability of forest tree species is essential for soil quality improvement of a nutrient deficient calciorthent with very high percentage of free CaCO3 (34%). Six multipurpose tree species were selected to investigate the effect of afforestation after 18 years of plantations on size and dynamics of LSOMs, e.g. dissolved organic carbon (DOC), microbial biomass carbon (MBC) and light fraction carbon (LFC) and also on soil respiration. LSOMs were estimated during four seasons: summer (June), autumn (September), winter (December) and spring (March) in 0–15 cm and 15–30 cm soil depths and in situ soil respiration was also measured during the corresponding periods. Afforestation by Eucalyptus tereticornis (Smith) increased soil organic carbon (SOC) of the surface 30 cm soil layer by 142% which was at par with Terminalia arjuna Bedd. and Albizia procera (Roxb.) Benth while 63% increase was found by Pongamia pinnata (Linn.) over control plot (3.10 kg ha−1 SOC). Soil under T. arjuna had the highest increase in the mean annual concentration of DOC (by 201%), MBC (by 413%) and LFC (by 263%) over control in the 30 cm soil layer followed by E. tereticornis. Among the LSOMs, LFC had the maximum contribution to SOC (9.61–11.71%) in the afforested plots up to 30 cm soil layer. The relationships among the three labile pools were highly significant. Mean annual soil respiration was highest in E. tereticornis plot which was at par with Acacia lenticularis (L.) Willd and A. procera, while it was lowest in T. arjuna plot. Thus, MBC was the most sensitive to afforestation and LFC was the largest reservoir of carbon among the three LSOMs. The results suggest that afforestation by the six multipurpose tree species had increased the LSOMs and soil respiration to different magnitudes. T. arjuna was found to be the most suitable plantation with highest increase in LSOMs and lowest respiration among the different plantations.