Soil microbial biomass dynamics in grassland and agroecosystem receiving varying resource quality soil inputs in dry tropics

Atwo year field experiments were conducted to evaluate the effect of land use conversion and management strategies variation through addition of varying resource quality soil inputs on soil microbial biomass dynamics, under rice-wheat-summer fallow crop sequence in tropical dryland agroecosystem. The treatments involved addition of equivalent amount of N through chemical fertilizer (CF) and three organic inputs, viz. Sesbania shoot (high quality resource, HQR), wheat straw (low quality resource, LQR) and Sesbania+wheat straw (mixed quality, MQR) besides control (CO) and grassland (GF). On annual mean basis, cultivation of grassland decreased the MBC (−51%) and MBN (−52%) level in soil. Relative to control, application of WS+SS considerably increased the level of MBC (+77%) and MBN (+87%) in soil, instead of SS, WS and CF. In all cultivated plots, a distinct seasonal and temporal variation in microbial biomass C and N were found contrary to GF. Both soil MBC and MBN level increased from rice to wheat period and reached maximum during summer fallow; during rice, the pattern in decreasing order was HQR>MQR>LQR>CF>CO; wheat period, MQR>LQR>HQR>CF>CO; summer fallow, MQR>LQR>HQR>CF>CO. It is concluded that cultivation exerts negative effects on the concentration of soil microbial biomass. Application of varying resource quality exogenous soil inputs maintains the microbial biomass level in soil, differentially. Addition of MOR was most effective for sustained buildup of microbial biomass in soil throughout the cycle, rather than HQR, LQR or CF. The fertility of soil in term of soil microbial biomass can be maintained by regulating the resource quality of exogenous inputs, and these results will help in designing the management strategies for sustaining long term soil fertility in these tropical dryland agroecosystem.

• Land use conversion from grassland to cropland significantly lowers the level of microbial biomass in soil.

• 1The application of single exogenous soil inputs, CF and WS resulted in much lower; SS showed marginal however, combined input SS+WS sustained higher microbial biomass throughout the annual cycle.