Inoculation of arbuscular mycorrhizal fungi can substantially reduce phosphate fertilizer application to Allium fistulosum L. and achieve marketable yield under field condition

The effects of inoculating arbuscular mycorrhizal (AM) fungi on the growth, phosphorus (P) uptake, and yield of Welsh onion (Allium fistulosum L.) were examined under the non-sterile field condition. Welsh onion was inoculated with the AM fungus, Glomus R-10, and grown in a glasshouse for 58 days. Non-inoculated plants were grown as control. Inoculated and non-inoculated seedlings were transplanted to a field with four available soil P levels (300, 600, 1,000, and 1,500 mg P2O5 kg(-1) soil) and grown for 109 days. AM fungus colonization, shoot P concentration, shoot dry weight, shoot length, and leaf sheath diameter were measured. Percentage AM fungus colonization of inoculated plants was 94% at transplant and ranged from 60% to 77% at harvest. Meanwhile, non-inoculated plants were colonized by indigenous AM fungi. Shoot length and leaf sheath diameter of inoculated plants were larger than those of non-inoculated plants grown in soil containing 300 and 600 mg P2O5 kg(-1) soil. Shoot P content of inoculated plants was higher than that of non-inoculated plants grown in soil containing 300 and 600 mg P2O5 kg(-1) soil. Yield (shoot dry weight) was higher for non-inoculated plants grown in soil containing 1,000 and 1,500 mg P2O5 kg(-1) soil than for those grown in soil containing 300 and 600 mg P2O5 kg(-1) soil. Meanwhile, the yields of inoculated plants (200 g plant(-1)) grown in soils containing the four P levels were not significantly different. Yield of inoculated plants grown in soil containing 300 mg P2O5 kg(-1) soil was similar to that of non-inoculated plants grown in soil containing 1,000 mg P2O5 kg(-1) soil. The cost of AM fungal inoculum for inoculated plants was US$ 2,285 ha(-1) and lower than the cost of superphosphate (US$ 5,659 ha(-1)) added to soil containing 1,000 mg P2O5 kg(-1) soil for non-inoculated plants. These results indicate that the inoculation of AM fungi can achieve marketable yield of A. fistulosum under the field condition with reduced application of P fertilizer.