Effects of Fertilization and Microbial Inoculants Applied at Transplanting on the Growth of Mexican Fan Palm and Queen Palm

Container-grown mexican fan palm (Washingtonia robusta) and queen palm (Syagrus romanzoffiana) transplanted into a field nursery having phosphorus (P)-sufficient and P-deficient soils were treated at the time of planting with four commercial microbial inoculants (each containing arbuscular mycorrhizal fungi, alone or with other microbial components or fertilizers), two fertilizers, or nothing (control). All but the control palms received applications of an 8N–0.9P–10K palm fertilizer every 3 months for 2 years. None of the treatments improved growth over the control in the P-deficient soil. In the P-sufficient soil, none of the microbial inoculants improved growth over that of similarly fertilized noninoculated palms. Discrepancies were observed regarding nonmycorrhizal fungi and bacteria present in the microbial inoculant products. The type and quantity of these microbes listed on the labels of the microbial inoculant products did not necessarily match the type and quantity actually detected in the products.