Arbuscular mycorrhizal fungi inoculation enhances phosphorus use efficiency and soybean productivity on a Haplic Acrisol

Abstract

There is a growing interest in the use of arbuscular mycorrhizal fungi to partially fulfil the high phosphorus need of legumes. Thus, this study hypothesised that, arbuscular mycorrhizal fungi inoculation would enhance phosphorus (P) uptake, growth and yield of soybean when combined with low P fertilizer rate (15 kg ha−1). A two-year field experiment was conducted on a Haplic Acrisol using two mycorrhizal isolates (Glomus mosseae and Rhizophagus irregularis) inoculated on two soybean lines (TGx 1989-48 FN and TGx 1989-75 FN). The treatments also included three levels of triple superphosphate (TSP) (0, 15, and 30 kg P ha−1). The treatments were arranged in a split-split plot design with three replications. The soybean lines, P rates and mycorrhizal isolates constituted the main-plot, sub-plot and sub-sub plot factors, respectively. Mycorrhizal inoculation combined with 15 kg P ha−1 gave the highest soybean root length colonization, shoot and grain P uptake, shoot biomass and grain yields which were statistically comparable to 30 kg TSP ha−1. Glomus mosseae showed higher soybean root length colonization and P uptake, which resulted in better soybean growth and yield improvement than R. irregularis. Furthermore, inoculation combined with 15 kg P ha−1 reduced soil microbial biomass P by stimulating P release by soil microbes and thus increased soil available P. However, G. mosseae inoculated plots showed higher performance in soybean root length colonization and P uptake, which consequently resulted in better P use efficiency than R. irregularis. Inoculation of mycorrhizal isolates combined with 15 kg P ha-1 gave the highest net benefit and marginal rate of return and is therefore economically profitable for soybean production. Inoculation with G. mosseae or R. irregularis combined with 15 kg P ha-1 is therefore a promising technology that can be used to enhance P uptake and soybean productivity. Future research should focus on understanding the long-term interaction of different benchmark soils, legume species and mycorrhizal species in order to select high quality infective propagules with long shelf life and efficiency under field conditions.