Field arbuscular mycorrhizal inoculation increased plant performance without phosphorus fertilizer supply of four promoted upland rice varieties in Madagascar

Summary In Madagascar, upland rice cropping is constrained by soil acidity and low phosphorus (P) bioavailability. Given their role in plant P nutrition, arbuscular mycorrhizal fungi (AMF) may improve crop yield in nutrient-poor tropical soils. In the Vakinankaratra region, a field experiment was conducted at 908 m asl on an acidic Ferralsol during the 2019–2020 growing season. The aim was to test the ability of four promoted rice varieties to respond to AMF seed-coating inoculation with a commercial strain of Rhizophagus irregularis in the absence or presence of P fertilizer (20 kg ha−1 of P2O5) under no expected nitrogen (N) limitation. In absence of P fertilization, both at tillering and at maturity and irrespective of the rice varieties, AMF inoculation significantly improved plant performance and finally grain yield, grain N, and grain P amounts by an average of 28%, 30%, and 39%, respectively. In contrast, when P fertilizer was supplied, no significant effect of AMF inoculation was observed. Rice growth variables were significantly higher with the application of P fertilizer than with AMF inoculation both at tillering and at maturity. P fertilizer without inoculation provided an average grain yield improvement of 85%. At tillering, mycorrhizal parameters for root colonization assessment were not positively linked with rice growth variables suggesting an early effect of AMF inoculation. We concluded that, with no P fertilization, AMF seed coating inoculation at the field scale significantly improved upland rice plant performance in a limited soil P environment. Our rice genetic variability did not interfere significantly both with mycorrhizal parameters and crop AMF inoculation benefits.