ENVIRONMENTAL QUALITY Commercial Microbial Inoculums and Their Effect on Plant Growth and Development: A Synopsis of Current Literature and Case Studies

Microbial competitive exclusion is an ecological approach that reduces resource access by pathogens, thereby hampering their development. Effective use of microbial inoculums can thus prevent pathogens from reaching economic thresholds and also enhance nutrient availability via increased microbial assimilation and nutrient cycling. Several research groups have demonstrated the effectiveness of this approach, and used inoculated compost to enhance crop resistance to soil plant pathogens. Development of commercial microbial inoculums aimed to enhance repressive soil properties can therefore improve crop performance and yields. Commercial microbial inoculums (MI) are generally marketed as individual microbe species or as a diverse mixture of microbes typically found in healthy soils. Use of microbial products with one or only a few species may hamper successful establishment of microbial populations in adverse soil environments. Creating favorable soil environment, on the other hand, appears to be critical, to boast overall effectiveness of MI in controlling soil pathogens. Application of microbial inoculums can be considered with any production system that includes organic amendments that provide an energy source for soil microbes. Examples include landscape bedding plant production, golf courses that regularly top-dress fairways with compost, ornamental container nursery stock as well as agronomic and vegetable crops that utilize organic amendments to provide a suitable substrate for beneficial soil microbes. Perhaps the greatest potential use and impacts of commercial microbial inoculums will be in enhancing productivity in developing countries since these regions have limited access to alternative approaches for pathogen control and improving inherent soil fertility.