Nursery inoculation with arbuscular mycorrhizal fungi improves yield of Allium fistulosum during a 3-year field trial

Using arbuscular mycorrhizal (AM) fungi in crop production for sustainable agriculture has attracted attention. The phosphorus (P) utilization efficiency of crops in Japan is approximately 20%, and the amount of P fertilizer applied is high. The purpose of this study was to determine the effect of nursery inoculation with AM fungi on the yield response of Welsh onion (Allium fistulosum L.) and to determine the effect of environmental factors on the yield response to AM fungal inoculation. Superphosphate was applied at rates of 0(P0), 500(P500) or 1,000 (P1000) P2O5 kg ha−1) in 13 fields in Japan from 2015 to 2017, and A. fistulosum seedlings inoculated with or without Rhizophagus sp. strain R-10 were transplanted. Yield and soil chemical characteristics (pH, NH4-N, NO3-N, Truog-P, exchangeable Ca, Mg, K, and cation exchange capacity) were measured, and multiple regression analysis was performed. The relative field mycorrhizal dependency (RFMD) was 15%, and inoculation significantly increased the yield of Welsh onion. The RFMD was positively affected by year, pH, NH4-N, and exchangeable Ca, and negatively affected by Truog-P, exchangeable Mg and K. These results indicate that it may be possible to replace P fertilization with AM fungi in Welsh onion production, regardless of the amount of available P in the soil, and that NH4-N may be an indicator of the use of AM fungi.