Cultivar-dependent soil microbial responses to contrasting nitrogen management strategies in Cenchrus purpureus systems with and without Clitoria ternatea

Abstract Background and aims In grass-based forage systems, integrating legumes can stimulate soil microbial communities, strengthen biogeochemical cycling, and reduce reliance on synthetic nitrogen inputs. However, soil responses may vary according to the grass cultivar. Cenchrus purpureus (Schumach.) Morrone cultivars contrasting in plant height, Mercker (tall) and Mott (dwarf), were evaluated under nitrogen-fertilised monoculture (300 kg N ha⁻ 1 yr⁻ 1 ) and intercropping with Clitoria ternatea L. without mineral nitrogen input, representing contrasting nitrogen management strategies. Methods Soil organic matter fractions, glomalin-related soil proteins, microbial biomass carbon and nitrogen, soil basal respiration, and microbial efficiency indices were assessed across seasons at 0–10, 10–20, and 20–40 cm soil depths using a randomised complete block design with four replications. Results Intercropping did not affect recalcitrant carbon pools (humic acid and humin) but increased fulvic acid carbon, particularly in Mercker-based systems. Seasonal variation exerted stronger control over humic and glomalin fractions than the cropping system. Mott + C. ternatea was associated with lower microbial biomass carbon, whereas basal respiration was not affected by cropping system. Mercker-based systems showed patterns potentially associated with greater microbial efficiency, whereas Mott + C. ternatea intercropping exhibited higher qCO₂ and more variable responses of qMIC and qMin across seasons and soil depths. Conclusions Greater belowground complementarity between the tall Mercker cultivar and C. ternatea was associated with patterns consistent with improved microbial metabolic efficiency indicators, suggesting potential effects on carbon stabilisation and microbially mediated nutrient cycling and highlighting the cultivar dependence of legume-based nitrogen supply in C. purpureus cut-and-carry systems.