Arbuscular mycorrhizal fungi biofertilization improves Cyperus esculentus growth, yield, and nutrient uptake while restoring degraded Paleudults in Southeastern Nigeria

Background Degraded Typic Paleudults in Southeastern Nigeria are characterised by strong acidity, severe phosphorus fixation, low organic matter, and depleted cation exchange capacity—conditions that severely constrain tigernut ( Cyperus esculentus L.) productivity and drive unsustainable mineral fertilizer dependence in smallholder farming systems. Circular agriculture requires biologically driven strategies that restore soil fertility, mobilise existing nutrient stocks, and reduce synthetic input reliance. Objective This study evaluated the effects of five Glomus species on tigernut growth, shoot nutrient concentrations, tuber yield, and key soil chemical properties on a degraded Typic Paleudult over two consecutive cropping seasons (2021–2022) at Ishiagu, Ebonyi State, Southeastern Nigeria. Methods A randomised complete block design with six treatments— Glomus intraradices (T1), G. deserticola (T2), G. fasciculatum (T3), G. etunicatum (T4), G. mosseae (T5), and an uninoculated control (T6)—replicated four times was maintained on the same plots across both seasons. Tigernut growth (plant height, tiller number, leaf number at 4, 6, 8 weeks after planting [WAP]), shoot nutrient concentrations (N, P, K, Ca, Mg at 6 and 8 WAP), tuber yield components (fresh and dry weight), and soil chemical properties were measured. Root colonisation was assessed by trypan blue staining and the gridline intersect method. Data were subjected to ANOVA and means separated with Fisher’s LSD at p  ≤ 0.05. Results AMF biofertilization significantly improved all measured variables relative to the uninoculated control. At 8 WAP in 2022, tiller number ranged from 9.23 plant −1 (control) to 17.80 plant −1 under G. fasciculatum (LSD = 1.30, p  ≤ 0.05); plant height increased from 15.88 cm (control) to 19.40 cm under G. fasciculatum (LSD = 1.30, p  ≤ 0.05); and leaf number rose from 14.10 (control) to 22.10 plant −1 under G. intraradices (LSD = 1.50, p  ≤ 0.05). Fresh tuber weight increased from 1.70 g plant −1 (control) to 3.10 g plant −1 under G. intraradices —an 82% yield gain (LSD = 0.30, p  ≤ 0.05). Shoot N concentration at 8 WAP ranged from 14.97 g kg −1 (control) to 32.68 g kg −1 under G. etunicatum (LSD = 4.33, p  ≤ 0.05). After two seasons, soil pH increased from 5.20 to 6.30, total N from 0.35 to 0.80 g kg −1 , CEC from 8.52 to 10.00 cmol(+) kg −1 , and base saturation from 22.71 to 29.50%—all significant at p  ≤ 0.05; however, because AMF-inoculated plots dominated the 2022 composite sample (20 of 24 plots), these soil changes represent plot-population averages and should be interpreted cautiously as plausibly AMF-mediated but not strictly causal without treatment-level replication. Conclusion Two-season AMF biofertilization significantly enhanced tigernut growth, tuber yield, shoot nutrient concentrations, and soil chemical quality on a degraded Paleudult without mineral fertilizer inputs, supporting its potential as a low-cost circular strategy to partially reduce synthetic fertilizer dependence and progressively restore soil fertility in tigernut systems in West Africa.