Growth and yield enhancement of lowland rice cultivars by arbuscular mycorrhizal fungi in phosphorus-deficient conditions

Phosphorus deficiency limits rice production in lowland savannah regions. This study investigated the effects of phosphorus deficiency and arbuscular mycorrhizal fungal (AMF) inoculation on lowland rice cultivars under varying water regimes. Two experiments were conducted at the Federal University of Agriculture, Abeokuta (FUNAAB), Nigeria. The pot experiment used a completely randomized design with three factors: water levels (150%, 100%, and 50% field capacity), phosphorus rates (60 kg P2O5 ha−1 and 0 kg P2O5 ha−1), and mycorrhizal species (Funneliformis mosseae, Rhizophagus irregularis, and no inoculation) in three replicates using ARICA 3. The field experiment employed a randomized complete block design mirroring pot treatments but included two rice varieties (NERICA L-34 and ARICA 3) and omitted water treatments. In the pot study, grain yield per plant under P-deficient conditions was 51% lower than in P-fertilized plots (2.16 g). AMF colonization was higher in P-deficient (35.4%) than P-fertilized (28.5%) treatments. Funneliformis mosseae induced the highest colonization (42.9%), while Rhizophagus irregularis produced the greatest grain number. In the field, NERICA L-34 outperformed ARICA 3 in panicle number (89.1 vs. 75.3) and grains per panicle. AMF-inoculated plants showed enhanced growth and yield, with Rhizophagus irregularis yielding the highest grain output (2.82 t ha−1), followed by Funneliformis mosseae (2.46 t ha−1) and control (2.11 t ha−1). Control plants exhibited low but detectable AMF colonization (13.7% in pots; 16.3% in field), attributed to native AMF in unsterilized soil. These results confirm that AMF inoculation can significantly improve rice performance in P-deficient lowland ecosystems, even under natural microbial conditions.