Soil microbial inoculation increases corn yield and insect attack

Abstract

Effective Microorganisms (EM®) is a "biofertiliser" soil inoculant, marketed as a crop yield enhancer. However, the literature has neither comprehensively reviewed its purported effects on harvests across multiple species nor investigated its effects on plant herbivore defence other than this group's previous research on tomatoes. Here a meta-analysis of 39 journal articles and a greenhouse experiment with nine crop species afforded a nuanced assessment of Effective Microorganisms' effects on plant growth and yield. Overall, in line with predictions, Effective Microorganisms showed significant positive effect on yield and growth (0.03 effect sizes increase) in the meta-analysis, and increased growth 16 % in the greenhouse, but with strong, and at times negative, species-specific responses. An additional potential benefit of Effective Microorganisms includes increased defence against herbivore attack, but inoculated corn (Zea mays) in a field and a greenhouse experiment exhibited decreased defences. Specifically, the field experiment demonstrated that Effective Microorganisms treatment corresponded to a 26 % reduction in predatory insect diversity on corn plants, while not improving growth or yield but did increase water uptake. A subsequent greenhouse experiment suggested likely physiological mechanisms behind the loss of predator diversity. When non-inoculated control corn plants were set upon by caterpillars of the herbivorous insect Spodoptera littoralis, the plants increased production of defensive volatile organic compounds (VOCs) by 272 %. Surprisingly, inoculation with Effective Microorganisms rendered greenhouse corn plants 51 % more palatable to S. littoralis. Further localised studies are, therefore, needed to efficiently incorporate Effective Microorganisms with either conventional or sustainable agricultural management systems.

The effect of pro-ecological procedures and plant injury on the content of free phenolic acids in winter wheat and on the feeding and development of Oulema melanopus

“…The beneficial effects of EM on soil properties, plant growth and the number of harmful organisms, including insect pests, are known. These beneficial effects thus reduce the negative effects of the cultivation simplifications in plant monoculture, while limiting the pressure of chemical products (used in plant protection) on the environment (Douglas 2007;Javaid and Shah 2010;Javaid and Bajwa 2011;Megali et al 2015). These microorganisms can regulate hormone signaling including the jasmonic acid and ethylene and salicylic acid pathways, thereby leading to gene expression, biosynthesis of secondary metabolites, plant defensive proteins and different enzymes and volatile compounds that may induce defenses against pest insects (Rashid and Chung 2017).…”

Effects of Soil Organisms on Aboveground Plant-Insect Interactions in the Field: Patterns, Mechanisms and the Role of Methodology

“…This process, better known as induced systemic resistance (ISR), can play an important role in plant-insect interactions in the field (Saravanakumar et al, 2008;Prabhukarthikeyan et al, 2014). Soil organisms can also interfere with plant volatile emissions, which are important cues for herbivores (e.g., for oviposition), as well as for many natural enemies, to detect host plants (Megali et al, 2015). Finally, several studies have shown that, for instance AMF can affect plant functional traits, such as flower size and stamen number (Gange and Smith, 2005;Gange et al, 2005a;Varga and Kytöviita, 2010).…”

Microbial Community Dynamics of Soybean (Glycine max) Is Affected by Cropping Sequence

“…Lastly, the C-S treatment had less bacterial diversity and richness compared to the Ca-S and S-S treatments, even at the pre-seeding treatment. Thus, soybean crops grown after corn may benefit from the addition of an inoculum that helps to promote bacterial diversity before the start of the growing season ( Megali et al, 2015 ; Beirinckx et al, 2020 ).…”