Impact of multiple soil microbial inoculants on biomass and biomass allocation of the legume crop field pea (Fabaceae: Pisum sativum L.)

Introduction

Food production is a global challenge and consequently there is considerable interest in manipulating the rhizobiome using microbial inoculants (MI) to support sustainable agriculture. The effectiveness of MI needs to be evaluated under diverse environmental conditions, especially for nitrogen-fixing legume crops, for which interactions between their associated bacteria and other soil biota may be particularly important.

Materials and Methods

We investigated how three commercially available types of plant growth-promoting MI, alone and in combination (B5: five species of Bacillus bacteria, GP: four species of Trichoderma fungi, N2: Paenibacillus polymyxa bacteria) impacted field pea (Fabales: Fabaceae, Pisum sativum L.) in the greenhouse and a 2-year field experiment.

Results

In the greenhouse, we found that effects of MI on plant performance varied, with positive effects of MI only apparent when plants were grown in the winter and likely under greater stress, because they lacked nodules. Plants grown in the summer had nodules and 2-week-old MI plants had less root biomass and total plant weight than noninoculated controls, but the weight of 4-week-old MI plants was similar to or greater than that of the controls. In the field, the root-to-shoot biomass ratio was highest in noninoculated controls and positive effects of N2 on shoots and B5 on shoots and pod densities did not translate into differences in pod weight or total plant weight. In most cases, plants inoculated with all three inoculants performed similar to those receiving a single inoculant, whereas root colonization by arbuscular mycorrhizal fungi was higher for B5 plants than plants in the other treatments.

Conclusions

Overall, B5 was the inoculant most often associated with increased plant biomass. This research underscores the need to consider microbial and environmental context when evaluating MI.