Organic carbon forms in Alfisol profile after Twenty Years of Cropping, Fertilization, Groundnut Shells and Farm Yard Manure Addition under Arid Conditions

The objectives of this study were to examine ;he effects of 20 years of groundnut cropping with chemical fertilization (NPK), organic manuring (FYM or groundnut shells) and integrated use of these two inputs (INM) on crop yields, soil organic carbon (SOC), particulate organic carbon (POC) and microbial biomass carbon (MBC) in an Alfisol under arid conditions. VariollS nutrient managcment options significantly «0.05) improved yield of groundnut pod over 20 years. The SOC improved significantly in surface layer (0-20 cm) from 0.31 % in control to 0.59 % in 50 % NPK + 4 t FYM ha". With 50 % NPK + 4 t groundnut shells ha" also the SOC improved markedly to 0.49 %. Interestingly, with integrated nutrient use, improvements in SOC were observed even up to 60 em depth of the profile. Overall, there was a buildup of SOC in surface layers in all treatments. Profile mean POC increased from 0,09 % in control to 0.20 % in 50 % NPK + 4 t FYM ha'!. Microbial biomass carbon (MBC) improved from 31.5-54,9 !-lg g'! soil in control to 39.5 -135,5 !-lg g'! soil with 50 % NPK + 4 t FYM ha", whereas the highest MBC/OC ratio was found in 50 % NPK + 4 t groundnut shells ho".