Response of Soil Phosphorus Required for Maximum Growth of Asparagus officinalis L. to Inoculation of Arbuscular Mycorrhizal Fungi

Fertilizer application efficiently increases crop yield, but may result in phosphorus (P) accumulation in soil, which increases the risk of aquatic eutrophication. Arbuscular mycorrhizal fungi (AMF) inoculation is a potential method to enhance P uptake by plant and to reduce fertilizer input requirements. However, there has been limited research on how much P application could be reduced by AMF inoculation. In this study, a pot experiment growing asparagus (Asparagus officinalis L.) was designed to investigate the effects of AMF inoculation and six levels of soil Olsen-P (10.4, 17.1, 30.9, 40.0, 62.1, and 95.5 mg kg−1 for P0, P1, P2, P3, P4 and P5 treatments, respectively) on root colonization, soil spore density, and the growth and P uptake of asparagus. The highest root colonization and soil spore density were both obtained in the P1 treatment (76% and 26.3 spores g−1 soil, respectively). Mycorrhizal dependency significantly (P < 0.05) decreased with increasing soil Olsen-P. A significant correlation (P < 0.01) was observed between mycorrhizal P uptake and root colonization, indicating that AMF contributed to increased P uptake and subsequent plant growth. The quadratic equations of shoot dry weight and soil Olsen-P showed that AMF decreased the P concentration of soil required for maximum plant growth by 14.5% from 67.9 to 59.3 mg Olsen-P kg−1. Our results suggested that AMF improved P efficiency via increased P uptake and optimal growth by adding AMF to the suitable P fertilization.