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The move towards more sustainable production agriculture will benefit growers and consumers. Protecting our planet requires collective action, innovation, and a commitment to balance productivity with environmental stewardship. The Food and Agriculture Organization (FAO) in a recent report “Sustainable Nitrogen Management in Agrifood Systems” warns that unsustainable nitrogen use in agriculture threatens human and environmental health, urging improved nitrogen use efficiency (NUE) to mitigate these risks. One area that can help this effort is utilizing microbial biologicals optimally.
Figure: Two most prominent beneficial plant-microbe interactions in nature are mycorrhizal associations, where fungi enhance plant nutrient and water uptake in exchange for carbon, and rhizobia-legume symbiosis, where Rhizobia bacteria fix atmospheric nitrogen in root nodules. Top Left: Arbuscular mycorrhizal fungi (AMF) spores and hyphae on roots aid in nutrient and water uptake; Top Right: Fluorescence-stained AMF inside root cells show fungal colonization; Bottom Left: Soybean root nodules containing Rhizobia bacteria; Bottom Right: Nodule cross-section reveals pink interiors, typically a sign of active nitrogen fixation.
Microbial biologicals utilizing beneficial microbes such as AMF and rhizobia bacteria have been hailed as sustainable natural alternatives to synthetic fertilizers. However, recent studies have raised doubts about the effectiveness of beneficial microbes and their commercialized versions in delivering substantial nutrition benefits to plants.
A recent study found limited evidence of nitrogen fixation in non-leguminous crops like cereals, reinforcing decades of research suggesting that bacterial inoculants may boost yields through plant-growth hormones rather than N₂ fixation. This questions the broad use of microbes as an independent solution to improve NUE.
Similarly, the soil health industry promotes microbial inoculants for yield, resilience, and carbon sequestration, but a University of Kansas (KU) study found 88% of commercial mycorrhizal products ineffective, often containing dead spores, hidden fertilizers, or pathogens, risking financial loss, environmental harm, and consumer mistrust. Additionally, overusing fertilizers and pesticides to control pests alongside microbial biologicals is counterintuitive, as they undermine the microbial communities these inoculants aim to enhance. This contradiction likely contributes to microbial inoculant failure.
Interestingly, microbial inoculants containing beneficial strains of Herbaspirillum seropedicae and Klebsiella variicola offer notable agricultural benefits; however, certain strains within these species have also been associated with potential human health risks, including reported cases of Herbaspirillum-induced pneumonia and antimicrobial resistance in K. variicola. Environmental stressors can compromise the mutualism between plants and endophytes by the induction of plant physiological responses and may lead to parasitism under extreme conditions.
Building Resilient Microbial Ecosystems: A Path to Sustainable Agriculture
While microbial inoculants hold potential, they alone cannot replace synthetic fertilizers, emphasizing the need for integration with other sustainable practices for optimal nutrient management. As the renowned ecologist Aldo Leopold once said, “The land is one organism. Its parts, like our own parts, compete with each other and co-operate with each other.” This interconnectedness underscores the importance of building microbial ecosystems that work in harmony with the soil, rather than relying on quick fixes that may disrupt this delicate balance. Rather than reapplying microbial inoculants frequently, we should focus on creating environments where these microbes can thrive long-term. We recommend the following steps:
1) Long-Term Monitoring: Tracking microbial dynamics with microbiome and soil health over time enables adaptive application methods, ensuring effective microbial introductions and lasting benefits for soil and crops. Monitoring interactions between inoculated and native soil microbes is key to preventing imbalances or competition. This ensures introduced microbes adapt and provide benefits without harming soil health or biodiversity.
2) Agroecological Practices for Supporting Microbial Ecosystems:
Agroecological practices like reduced tillage, cover cropping, integrated pest management and companion planting enhance microbial ecosystems by improving soil structure, reducing oxidation, and maintaining organic matter for a stable, nutrient-rich habitat. Integrating these practices would gradually rebuild soil biology and restore soil carbon reserves over time enhancing microbial effectiveness.
3) The Role of Soluble Carbon and Charge Balance:
An often-overlooked factor in microbial success is the role of soluble organic matter (SOM). Restoring soil organic carbon through carbon-based biostimulants produced via multi-step fractionation processes enhances soil health by optimizing soil redox potential and charge balance. A multi-step process selectively concentrates and recombines bioactive compounds (secondary metabolites) that are absent in carbon-based products derived from conventional one-step fractionation, enhancing their functional benefits. This will prevent imbalances from carbon oxidation in overworked fields that can disrupt nutrient availability and microbial redox activity. Soluble carbon also serves as a crucial food source for soil microbes, fueling their activity and ensuring their survival. This would strengthen the soil microbiome and reduce the need for microbial reapplications. H-85™ is an excellent example of a superior soluble carbon source.
4) Informed Use of Microbial Biologicals
Buyers must carefully navigate the microbial market to prevent inefficacy and unintended ecological impacts, requiring stricter regulations, validated modes of action, field-tested results, improved quality control, transparent labeling, independent testing, global standards, and locally sourced native microbe products. Establishing industry reliability and consumer trust is essential for unlocking this potential.
The Path Forward: A Holistic Approach to Sustainable Agriculture
To maximize microbial inoculant efficacy, growers should combine regulated microbial solutions with soluble carbon inputs and sustainable farming practices to restore soil and plant charge balance, support microbial health, and minimize environmental stress from excessive fertilizers and pesticides. Educating growers and agronomists on these principles can accelerate the adoption of practices that enhance microbial performance while maintaining ecological balance. As environmentalist John Muir wisely noted, “When we try to pick out anything by itself, we find it hitched to everything else in the Universe.” This interconnectedness underscores the importance of holistic agricultural approaches, reminding us that every decision impacts the broader ecosystem.
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