Impact of Organic and Inorganic Nutrient Management on Soil Carbon Fractions and Indices Under Soybean–Wheat Cropping in a Vertisol

A field experiment was conducted in a Vertisol and the effect of various bio inputs and recommended doses of fertiliser (RDF) was studied on soil organic carbon (SOC) fractions and carbon management indices under soybean–wheat cropping sequence in central India. The experiment consisted of seven treatments with four replications in randomised block design (RBD) such as T 1 : Organic manure (OM); T 2 : Biodynamic preparation (BP); T 3 : T 1 + panchagavya (PG); T 4 : T 1 + T 2 ; T 5 : T 2 + T 3 ; T 6 : No fertiliser/manure; and T 7 : Inorganic fertiliser (IF). Organic manure was supplied as cattle dung manure on nitrogen equivalent basis for soybean. For wheat crop a mix of three manures prepared from cattle dung, earth worms and poultry in a 1:1:1 proportion on N equivalent basis were supplied. The treatments receiving organic inputs with or without PG and BP improved total organic carbon (TOC) and SOC fractions viz. Walkley‐Black easily oxidizable soil organic carbon (WBC), acid hydrolyzable carbon (AHC), resistant carbon (RC), particulate organic matter carbon (POM‐C), potassium permanganate oxidizable carbon (KMnO 4 ‐C), water soluble carbon (WSC) and microbial biomass carbon (MBC). Increases in SOC fractions ranged between 8% and 73% over the IF. Soil carbon indices, including the Carbon Pool Index (CPI), Carbon Lability Index (CLI) and Carbon Management Index (CMI), were markedly higher under organic nutrient treatments than under inorganic treatment. The CMI increased by 64%–72% with organic amendments, indicating improved soil organic carbon dynamics and more effective carbon management under organic nutrient regimes.