In the unrelenting battle against climate change, soil organic carbon (SOC) stands as a pivotal ally, intimately linking terrestrial ecosystems to global carbon cycles. Despite its vital role in climate mitigation and agroecosystem productivity, the persistent decline of SOC stocks—driven by intensive agriculture and land-use changes—continues to raise alarms. Addressing this challenge, a groundbreaking study derived from the Broadbalk Classical Experiment at Rothamsted Research, the world’s longest-running continuous winter wheat trial, brings unprecedented insights into how over 180 years of mineral fertilization with nitrogen (N) and phosphorus (P) reshapes soil carbon dynamics. This research, leveraging an integrative approach combining radiocarbon (^14C) labelling, metagenomics, and metabolomics, uncovers intricate mechanistic shifts in soil microbial processes and carbon stability that redefine our understanding of nutrient input effects on carbon sequestration.
The Broadbalk experiment, established in the mid-19th century, uniquely positions scientists to probe century-spanning interactions between fertilization regimes and soil organic matter evolution. Historically, the merits and drawbacks of mineral fertilizers have been debated with respect to SOC balance. While fertilization boosts crop yields, its influence on soil carbon accumulation has remained ambiguous due to complex feedbacks within soil microbiomes and plant residue turnover. Through the innovative fusion of molecular tools and long-term field data, researchers now illuminate how distinct fertilization strategies orchestrate carbon partitioning between labile pools susceptible to microbial degradation and mineral-associated fractions more resistant to decomposition.
One of the salient findings is that phosphorus application alone engenders a remarkable 37% increase in microbial respiration coupled with a 20% rise in microbial biomass, paradoxically limiting the accrual of stable carbon forms. This implies that P fertilization predominantly fuels microbial activity, expediting the decomposition of plant residues without proportionately enhancing carbon stabilization. In contrast, nitrogen fertilization singularly accelerates microbial carbon use efficiency along with necromass accumulation — microbial-derived organic matter remnants — thereby fostering the buildup of mineral-associated carbon which is crucial for long-term soil carbon persistence. These divergent microbial responses unravel the nutrient-specific pathways through which fertilization modulates SOC fate.
The synergistic effect of combined NP fertilization emerges as particularly compelling. By simultaneously elevating plant-derived carbon inputs and promoting microbial transformation of labile carbon into more refractory, stable forms, NP fertilization substantially augments both the quantity and stability of soil organic carbon stocks. This enhanced carbon sequestration potential signifies a holistic improvement in soil quality and resilience, reinforcing the rationale for balanced nutrient management in agroecosystems. The integration of multi-omics and isotope tracing thus exposes how nutrient synergy transcends simple additive effects, engendering novel biochemical networks that underpin enhanced SOC formation.
Further contextualizing these findings, a global meta-analysis reveals that the influence of mineral fertilization on SOC demonstrates a temporal dimension characterized by initial declines followed by progressive increases after extended durations—specifically beyond 16 years for nitrogen and 34 years for phosphorus application. Such temporal dynamics underscore the necessity of long-term perspectives in evaluating soil carbon responses, as short-term studies may overlook critical stabilization processes that mature over decades. The persistence of these effects across diverse cropland systems highlights the widespread potential of mineral fertilization to serve as a climate mitigation lever at scale.
The study’s amalgamation of ^14C radiolabelling techniques elucidates carbon turnover rates and transformation pathways with unprecedented resolution. By tracing carbon derived explicitly from plant residues and microbial activity, the research deciphers fluxes between labile and mineral-associated pools. This differentiation is crucial, as it identifies the fractions of SOC that are vulnerable versus resistant to microbial decomposition — determining the longevity of carbon storage. The findings suggest that nitrogen fertilization enhances the efficiency of microbial necromass incorporation into mineral-associated soil fractions, thereby stabilizing carbon over extended periods.
Metagenomic analysis further deciphers the functional shifts within soil microbial communities driven by distinct nutrient inputs. Nitrogen fertilization uniquely selects for microbial taxa and functional genes implicated in necromass production and carbon stabilization, while phosphorus primarily stimulates taxa associated with accelerated carbon mineralization. These shifts impact not only carbon cycling but broader nutrient transformations, soil structure, and aggregate stability. The integration of functional microbial ecology into soil carbon research elevates our mechanistic understanding and enables predicting fertilization impacts beyond singular biochemical reactions.
Metabolomic profiling completes the triad by revealing nutrient-induced changes in soil biochemical milieu. Alterations in metabolite composition reflect microbial metabolic states and exudate patterns, with NP fertilization fostering a suite of compounds that facilitate carbon polymerization and mineral binding. This biochemical environment, rich in carbon-complexing molecules, enhances organic matter protection from enzymatic breakdown, linking chemical innovation to ecological function. Such insights pave the way for designing targeted interventions to amplify soil carbon stabilization through manipulating microbial metabolite dynamics.
The broader implications of this research resonate deeply with global sustainability goals. With agricultural soils occupying vast terrestrial areas, their management represents a formidable opportunity for climate mitigation. However, maximizing SOC sequestration requires nuanced fertilization strategies that transcend yield optimization to embrace long-term soil health and carbon balance. The demonstrated efficacy of combined nitrogen and phosphorus applications in amplifying carbon stocks and stability offers a pathway to reconcile intensive crop production with environmental stewardship.
Moreover, these findings challenge the paradigm of nutrient application uniformity, advocating instead for ecologically informed nutrient regimes tailored to soil microbial ecology and carbon cycling processes. The nuanced, decadal-scale observations stress the importance of policy frameworks and agricultural practices that integrate long-term soil monitoring and adaptive fertilization schemes. This will be critical to harness soil’s full potential as a carbon sink while mitigating nutrient runoff and pollution risks.
From a methodological perspective, this study exemplifies the power of interdisciplinary approaches combining classical agronomic experiments with cutting-edge molecular and isotopic tools. The ability to unravel century-scale soil processes down to microbial functional gene shifts and metabolite transformations signals a new era in soil science. Such integrative strategies are essential to decode the complexity of soil biogeochemistry, bridging scales from microscale microbial interactions to global biogeochemical cycles.
In conclusion, the enduring legacy of the Broadbalk Classical Experiment continues to yield transformative insights into soil carbon dynamics under mineral fertilization. By dissecting the differential effects of nitrogen and phosphorus inputs on microbial activity, carbon use efficiency, and stabilization pathways, this research delineates clear mechanistic underpinnings of SOC sequestration. It affirms that long-term balanced fertilization not only supports robust crop yields but also enhances soil carbon reservoirs crucial for climate change mitigation. As global agriculture grapples with sustainability challenges, these findings illuminate a viable path to aligning productivity with planetary health through informed nutrient stewardship.
The road ahead beckons further exploration into the mechanistic nuances of nutrient-driven soil carbon dynamics across diverse climatic zones and cropping systems. Elucidating the interactions with other soil amendments, organic inputs, and emerging biotechnologies will be vital to fully unlock soil’s potential as a climate ally. Yet, the clarity achieved by this landmark study sets a foundational benchmark, demonstrating that judicious management of nitrogen and phosphorus fertilization is an effective strategy for safeguarding soil carbon stocks—and by extension, the future of both farming and the planet.
Subject of Research: Long-term effects of nitrogen and phosphorus fertilization on soil organic carbon dynamics and microbial-mediated carbon sequestration in agricultural soils.
Article Title: Soil carbon sequestration enhanced by long-term nitrogen and phosphorus fertilization.
Article References:
Tang, S., Pan, W., Yang, Y. et al. Soil carbon sequestration enhanced by long-term nitrogen and phosphorus fertilization. Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01789-y
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