Cutting N2O without cutting yields: a case for microbial bioinputs

1 Introduction

Atmospheric emissions of nitrous oxide (N₂O) have increased by approximately 40% since 1980, with agriculture being the main source. This trend places N₂O mitigation at the center of both climate and agricultural sustainability agendas, moving the world further from the 1.5°C target and slowing ozone layer recovery, as N₂O is now the main ozone-depleting gas (Tian et al., 2024).

Nitrous oxide emissions arise from multiple nitrogen transformation pathways, including nitrification, denitrification, and coupled microbial processes. The relative importance of which depends on soil properties, climate, management practices, and microbial community composition (Malyan et al., 2025). Meanwhile, fertilizer price fluctuations continue to strain farm budgets. Global food prices remained volatile even after the 2022 peak. The science is clear: when crops receive more synthetic nitrogen (N) than they can absorb, these diverse pathways converge on a shared inefficiency, and part of the surplus N is lost to the environment as N₂O emissions.

However, the policy response has favored subsidies over efficiency. A practical solution already exists: microbial bioinputs, such as plant growth-promoting bacteria (PGPB), help farmers maintain yields while reducing synthetic N use by enhancing root growth, nutrient uptake, and metabolic efficiency. Therefore, the central challenge is no longer proof of concept but rather governance and deployment at scale. This includes clear standards, multicenter trials, and on-farm measurement, reporting, and verification (MRV) of N₂O emissions.

Here, we argue that integrating microbial bioinputs within this framework represents a near-term opportunity to reduce agricultural N₂O emissions without compromising yields. This conceptual framework is summarized in Figure 1, which illustrates how microbial bioinputs can reduce synthetic N use, enhance N efficiency, and enable credible emission accounting through standards, multi-center trials, and MRV systems.

Figure 1

Figure 1. Conceptual framework linking microbial bioinputs to reduced agricultural N₂O emissions. The left panel depicts conventional fertilizer-intensive systems as major sources of N₂O, a potent greenhouse and ozone-depleting gas. The center panel illustrates how microbial bioinputs, such as Azospirillum and other plant growth-promoting bacteria, enhance root development, nutrient uptake, and nitrogen-use efficiency, allowing 20-30 kg N ha⁻¹ less fertilizer without yield loss. The right panel shows enabling governance measures, including quality standards, multicenter trials, and on-farm measurement, reporting, and verification (MRV) systems that integrate verified emission reductions into national greenhouse gas inventories. Together, these elements highlight a scalable approach to reduce N₂O emissions while maintaining crop productivity.

2 What the field evidence shows (without the hype)

Field-scale evidence indicates that microbial bioinputs can reduce synthetic nitrogen (N) requirements while maintaining crop yields, although the responses are context-dependent (Barbosa et al., 2025). A Brazilian meta-analysis of 103 maize trials showed consistent benefits from Azospirillum brasilense: inoculation led to larger root systems, higher leaf N, and yield gains, especially with seed inoculation (Barbosa et al., 2022). This case represents one of the most comprehensive and mature datasets currently available, derived from multi-year, multi-site trials conducted under commercial farming conditions.

In suitable environments, farmers can reduce N fertilizer by 20-30 kg N ha⁻¹ without a yield penalty, substituting approximately 25% of side-dressed N (Hungria et al., 2022). Although much of the strongest field-scale evidence comes from Brazilian maize systems, yield-preserving reductions in N fertilizer have also been documented in other crops, including wheat (Shaaban et al., 2025), rice (Mattos et al., 2023), and lettuce (Consentino et al., 2022), when microbial bioinputs are appropriately matched to soil, climate, and management conditions.

However, responses vary with strain, soil, climate, and management practices, a pattern consistently observed across regions and crop species, highlighting the need for targeted use based on the field data. This variability underscores the central argument of this Opinion: that microbial bioinputs are ready for scale only when supported by multicenter trials, standardized protocols, and transparent reporting frameworks.

3 The thesis

Countries can reduce N₂O emissions and maintain crop yields by combining reduced mineral N inputs with proven microbial bio-inputs. Importantly, the key instruments required to support this transition (standards, coordinated field validation, and measurement frameworks) are already being developed and applied through international initiatives but remain insufficiently integrated. However, this approach will only work if trust is built around these products and services. Three elements are essential: (1) clear quality standards, (2) multicenter trial networks across crops, soils, and climates, and (3) fit-for-purpose MRV systems that ensure that efficiency gains are translated into credible climate accounting. Rather than proposing entirely new mechanisms, this Opinion advocates for the coordinated deployment of existing international tools to accelerate adoption and impact.

3.1 Standards and labeling

At a minimum, regulations should require strain identification, viable cell counts, contaminant limits, and shelf life verification by independent assessment. These requirements are already reflected in emerging international regulatory frameworks, including the EU Fertilizing Products Regulation (FPR) 2019/1009, which provides a harmonized market pathway (CE-marking) for microbial biostimulants alongside national routes (Biorefine Cluster Europe, 2023). These frameworks offer practical references for countries seeking to establish or strengthen national standards and reduce the proliferation of low-quality products that undermine farmer confidence.

3.2 A multicenter trial network with open protocols

The goal is not to conduct more isolated trials but to create probability maps showing where microbial bioinputs are most effective. This approach is consistent with international calls for harmonized multicenter agronomic testing across environments, supported by public–private consortia, crop boards, and extension services. Public–private partnerships should pre-register protocols, share metadata (soil chemistry, weather, and management), and publish all results, including negative findings.

Crop boards and extension services can host a tied trial system (research plots → strip trials → commercial fields) using standard data templates to enable annual meta-analyses. Such coordinated trial infrastructures already exist in a fragmented form and could be rapidly aligned to support microbial bioinput evaluation at scale. This is translational R&D: we are no longer discovering new microbes but their fit-for-purpose use.

3.3 MRV for N₂O that farmers can use

National inventories follow the 2019 IPCC Refinement (IPCC, 2019), but on-farm programs require practical tools to measure N₂O fluxes and perform transparent calculations. Existing international MRV guidance provides a strong foundation, including standardized chamber methodologies and flux calculation protocols developed by the Global Research Alliance on Agricultural Greenhouse Gases (de Klein et al., 2020).

These tools can support pilot MRV systems that estimate local emission factors and link verified N savings to climate finance and green procurement. By building on internationally recognized IPCC-aligned methodologies, such MRV systems can ensure credibility while remaining accessible to farmers and to extension services. Credibility is key: if a microbial inoculant allows farmers to reduce N application by 15%–25% without lowering yield, that should be counted in both carbon math and farm profitability.

4 Why this reasoning withstands counterarguments

Skeptics raise three valid concerns:

– “It won’t work everywhere”: Correct, which is why we need multi-site trials and targeted deployment. Meta-analyses have already shown environment-sensitive responses (Barbosa et al., 2022). A trial network converts uncertainty into a probability map.

– “Verification is hard”: Also true but not new. MRV toolkits exist, including standardized chamber methods, flux calculation protocols, and inventory systems that are already being used by countries. Pilots can start in a few agroecological zones and scale with learning.

– “Fertilizer prices fell; urgency fades”: Food prices have dipped since the 2022 peak, but volatility remains. Efficiency is a hedge against market swings and climate necessity. Paying for nutrient efficiency rather than input volume is a sound policy.

5 Policy in twelve months: who should do what

The actions outlined below are intended as near-term, realistic entry points rather than full-scale implementation targets. While structural constraints, such as limited institutional capacity, funding availability, regulatory inertia, and farmer adoption barriers, may slow deployment, the next 12 months represent a critical policy window to initiate coordination, pilots, and enabling frameworks rather than to deliver complete system transformation.

– Standards agencies and agriculture ministries: Adopt national standards for microbial bioinputs aligned with the EU-style FPR (Biorefine Cluster Europe, 2023). Identity, quality, safety, and labeling are required. Although regulatory development may be constrained by technical capacity and administrative timelines, initiating stakeholder consultations, drafting guidelines, and implementing pilot certification schemes within 12 months is feasible and impactful. Create a public registry of compliant products and approved strains.

– Research councils and development banks: Fund a multicenter inoculant trial network focused on priority crops and regions with high fertilizer costs. Open protocols, data sharing, and annual meta-analyses should be ensured to refine deployment. Given funding cycles and logistical constraints, initial investments can prioritize pilot regions and leverage existing trial infrastructures, scaling progressively as evidence and capacity grow.

– Inventory teams and environmental ministries: Launch pilot MVR programs for N₂O using IPCC 2019 and Global Research Alliance protocols (de Klein et al., 2020). Integrate results into national inventories to reduce uncertainty and improve emission reduction crediting. Recognizing the technical and financial barriers associated with on-farm N₂O measurements, early efforts can focus on simplified methodologies, proxy indicators, and capacity building before nationwide rollout.

– Procurement agencies and farm-credit programs: Link public procurement and concessional credit to nitrogen-use efficiency (NUE) milestones (e.g., 15%–25% verified N savings with yield parity, so that markets reward outcomes). Adoption challenges and risk aversion among farmers can be mitigated through transitional incentives, technical assistance, and risk-sharing mechanisms in the early phases.

– Industry and producer groups: Co-finance field trials, provide seeds and inoculants at cost in pilot regions, and commit to data transparency, including non-significant results that help refine targeting. Although commercial incentives may initially limit participation, early engagement in pilot programs can reduce uncertainty and build long-term market confidence.

6 Five-year success metrics

The metrics proposed below are intended as indicative, outcome-oriented benchmarks rather than fixed or universally applicable thresholds. They are designed to reflect the plausible ranges reported in field studies and synthesis analyses while recognizing that outcomes will vary across crops, regions, and policy contexts.

1. At least 20% reduction in applied synthetic N in targeted crop-region combinations, with yield parity in at least 70% of trials: These values are not prescriptive targets but illustrative benchmarks aligned with reductions and yield responses commonly reported in field experiments and meta-analyses of microbial bioinputs. The actual performance depends on the crop type, baseline N rates, soil properties, climate, and management practices.

2. Verified N₂O emission reductions via third-party MRV integrated into national inventories: While emission estimates are subject to methodological uncertainty, the use of IPCC-aligned and internationally recognized MRV protocols ensures comparability and credibility across programs and regions.

3. Cost per ton of CO₂-equivalent avoided competitive with other mitigation options: This metric is intended for comparative evaluation at the program or portfolio level, rather than as a farm-level performance indicator, and will vary with fertilizer prices, carbon valuation, and policy incentives.

4. Stable or improved farmer profit margins: We acknowledge that farm profitability is influenced by external factors such as input prices, commodity markets, and policy instruments. Nevertheless, this indicator remains relevant as a complementary metric when interpreted alongside agronomic performance and verified N savings, ensuring that climate mitigation does not come at the expense of farmer livelihoods.

5. An open data platform of trial results that refines targeting strategies over time: This qualitative metric emphasizes transparency and learning rather than numerical thresholds, enabling the continuous improvement of deployment strategies as evidence accumulates across environments and production systems.

7 Why this belongs on the near-term climate agenda

The 2024 Global N₂O Budget confirms an accelerating agricultural signal (Tian et al., 2024). Without intervention, N₂O alone could compromise global efforts to achieve the Paris targets. The good news is that microbial bioinputs are not speculative in nature. They are already in use and show consistent agronomic benefits, especially in low- to medium-input systems when matched to local environments. What is missing is the system around them (standards, trials, and MRV) to convert better N use into climate benefits. With these elements in place, countries can reduce N₂O without sacrificing yields, strengthening food security, supporting farmer incomes, and delivering measurable climate gains. This is the kind of pragmatic, near-term solution that both climate and food agendas urgently need.

Author contributions

CG: Funding acquisition, Writing – original draft, Conceptualization, Project administration, Supervision. LM: Software, Writing – review & editing, Methodology. RS: Project administration, Funding acquisition, Writing – original draft, Supervision, Conceptualization.

Funding

The author(s) declared that financial support was received for this work and/or its publication. Research in Raul Sperotto’s laboratory is currently funded by CNPq (National Council for Scientific and Technological Development—Grants 405779/2022–4 and 305135/2021-0) and FAPERGS (Rio Grande do Sul State Research Funding Foundation—Grant 22/2551-0001641-3). Research in Camille Granada’s laboratory is currently funded by CNPq (Grant 408680/2024-5) and FAPERGS (Grant 24/2551-0000656-7).

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

The author RS declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision.

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