Background: Rhizosphere processes control soil carbon stabilization and nitrogen cycling in cereal-based dryland systems. Pearl millet (Pennisetum glaucum [L.] R. Br.) is a staple crop of semi-arid tropics but the interactive effects of combined organic–inorganic fertilization on the biogeochemistry of its rhizosphere are still insufficiently characterized.
Objective: The present study was conducted to elucidate the mechanisms by which integrated nutrient management (INM) influences the rhizosphere-mediated stabilization of carbon (C) and nitrogen (N) cycling in P. glaucum under semi-arid conditions.
Methods: For two consecutive cropping seasons, a randomized complete block design (RCBD) experiment was conducted with seven fertilization treatments namely controls, sole inorganic (100% recommended dose of fertilizer, RDF), sole organic (farmyard manure, FYM) and combined organic-inorganic regimes. Quantitative PCR and metagenomic profiling of rhizosphere and bulk soils were used to quantify microbial biomass C and N (MBC, MBN), enzyme activities (dehydrogenase, urease, β-glucosidase, phosphatase), carbon fractions (particulate organic carbon (POC) and mineral-associated organic carbon (MAOC)) and functional genes (nifH, amoA, nosZ).
Results: The combined fertilization (T6: vermicompost + 100% RDF) significantly increased rhizosphere MBC (624 µg g(-1)) and MBN (101 µg g(-1)) over unfertilized control (218 and 31 µg g(-1), respectively). MAOC fractions increased by 155% under T6 relative to T0, and accounted for up to 38.9% of total SOC through microbial necromass. β-glucosidase activity was doubled under combined treatments. nifH gene copy numbers reached 1.8 × 10 7 copies g −1 soil. The nitrogen use efficiency (NUE) increased from 38.4% (T0) to 81.2% (T6) with a net N mineralization increase of 167%.
Conclusion: The combined organic–inorganic fertilization greatly improves rhizosphere microbial activity, stabilizes carbon pools through microaggregate occlusion and organo-mineral association, and enhances N cycling efficiency in P. glaucum systems. These findings highlight the agronomic and ecological importance of INM strategies for the sustainable management of soil health in dryland agroecosystems.