The study was designed to address a persistent gap in soil ecology. Although many investigations have examined how fertilization affects individual groups of soil organisms, comparatively few have traced the consequences across the entire food web, spanning microbes at the base to earthworms near the top, and fewer still have done so over a time frame long enough to capture the slow, cumulative changes that define soil health. To fill that gap, a team of researchers led by first and corresponding author Professor Yunfeng Chen of the Hubei Academy of Agricultural Sciences compared four long-term treatments: chemical fertilizer supplying nitrogen, phosphorus and potassium, known as NPK; organic manure alone; a combined treatment of manure plus NPK; and an unfertilized control plot that served as the experimental baseline.

The measurement strategy was deliberately broad. Rather than tracking a single indicator organism, the team quantified biomass or abundance across key taxonomic and functional groups, including microorganisms, protozoa, nematodes, mites, collembolans, enchytraeids and earthworms. They also calculated nematode ecological indices, a set of established metrics that soil ecologists use to infer the structure and maturity of soil food webs. Together, these measurements allowed the researchers to evaluate the relative strength of two competing regulatory forces: bottom-up control, in which the availability of resources such as organic carbon and nutrients determines how many organisms higher trophic levels can support, and top-down control, in which predators and higher consumers suppress or structure the populations below them.

The headline finding was unambiguous. Long-term fertilization increased the inputs of resources entering the soil, and that surge in resources enhanced most of the functional groups the team measured. Fertilized plots supported larger and more complex communities than the unfertilized control, confirming that sustained nutrient management is a powerful lever for shaping the living architecture of agricultural soils. But the differences among fertilization strategies proved just as consequential, and here the organic treatments stood out clearly.

Manure alone and the combined manure-plus-NPK treatment outperformed pure chemical fertilizer across most groups. When the researchers expressed these gains as relative increases compared with the NPK treatment, the manure plots showed improvements ranging from 20.69 to 972.52 percent, with an average of 241.62 percent, while the combined plots ranged from 26.55 to 792.30 percent, averaging 189.02 percent. Those are not marginal differences; they represent order-of-magnitude shifts in the abundance of some soil organisms. The practical implication is that organic amendments, whether applied alone or alongside mineral fertilizers, deliver substantially more nourishment to the soil food web than chemical fertilizer alone.

Interestingly, the manure-only and combined treatments did not differ significantly from each other. The researchers attribute this convergence to high soil fertility: once fertility reaches a sufficiently high level, the distinction between the two organic approaches diminishes, and both support similarly rich communities. In other words, the food web appears to saturate, and beyond a certain threshold of resource abundance, adding mineral fertilizer on top of manure yields little additional biological benefit even though it may still matter for crop nutrition.

The evidence for bottom-up regulation was strong and came from multiple independent lines. Functional groups showed positive correlations with one another, a pattern consistent with resources flowing upward through the web and lifting every level together rather than predators imposing their own structure from above. The enrichment index, a nematode-based metric that signals an abundance of opportunistic, resource-responsive organisms, rose by 51.27 percent under manure and 28.49 percent under the combined treatment relative to chemical fertilizer alone. The enrichment footprint, a complementary measure that captures the cumulative enrichment signal across the food web, increased even more dramatically, by 11.80 percent under manure and 47.17 percent under the combined treatment relative to NPK.

To synthesize these patterns into a causal framework, the team employed partial least squares path modeling, a statistical technique well suited to disentangling direct and indirect pathways among correlated variables. The modeling confirmed what the correlations and indices had suggested: bottom-up forces predominantly determined both the structure and the total biomass of the soil food web. Resource availability, shaped by decades of fertilization, was the dominant driver, while top-down influences played a comparatively minor role in this system. For a rice–wheat rotation, where flooded and aerobic phases alternate and organic matter dynamics are complex, this finding provides a clear conceptual anchor for future soil management research.

The implications extend well beyond the experimental plots. Soil food webs underpin essential ecosystem services, including decomposition, nutrient mineralization, suppression of plant pathogens and the maintenance of soil structure. A food web enriched through bottom-up channels is, in effect, a soil with greater biological capacity to sustain crop productivity over time. The study suggests that sustained organic inputs, particularly when integrated with mineral fertilizers, effectively enhance both the complexity and the size of the soil food web primarily through this bottom-up regulatory mechanism. For farmers and policymakers weighing the trade-offs between organic and conventional inputs, the results add a biological argument in favor of manure-based strategies, whether used alone or in combination with chemical fertilizer.

The research also carries a cautionary note for the long term. Because the experiment spanned thirty years, it captured changes that short-term studies inevitably miss, including the slow accumulation of soil organic matter and the gradual response of larger, slower-reproducing organisms such as earthworms and enchytraeids. The authors’ conclusion is that fertilization is not merely a plant nutrition tool but a food-web engineering instrument, and that its effects compound over decades. As agriculture worldwide faces pressure to maintain yields while restoring degraded soils, this long-term evidence from a major cereal rotation offers a template: feed the base of the soil food web, and the rest of the web, along with the services it provides, is likely to follow.

Subject of Research: Long-term effects of chemical and organic fertilization on the soil food web in a rice–wheat cropping system

Article Title: Long-term fertilization enriches soil food web mainly through bottom-up regulation in a rice–wheat cropping system

Article References: Long-term fertilization enriches soil food web mainly through bottom-up regulation in a rice–wheat cropping system. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: soil food web, long-term fertilization, rice–wheat rotation, bottom-up regulation, manure, NPK fertilizer, nematodes, earthworms, soil fertility, enrichment index, agroecology, soil biodiversity

The vitality of healthy soil hinges fundamentally on the presence of stable soil aggregates and sufficient soil organic carbon. These two factors form an intricate synergy critical for maintaining water retention, nutrient cycling, root support, and erosion resistance within soil ecosystems. Notwithstanding their importance, a vast proportion of agricultural soils worldwide struggle with carbon insufficiency. Conventional organic amendments have historically exhibited limited success in simultaneously bolstering both soil carbon stocks and the physical integrity of soil aggregates, often falling short in delivering comprehensive soil health improvements.

Challenging this paradigm, the latest experimental research, published in the journal Biochar, delves into the comparative efficacy of hydrochar against maize straw and straw-derived biochar within the context of purple soil—a prevalent agricultural substrate across China. Importantly, the study diversifies its examination by investigating hydrochars derived from varied feedstocks, including maize straw, pig manure, and Zanthoxylum stalks. This multidimensional approach provides pivotal insights into how feedstock choice influences hydrochar’s functional properties and tailorability.

Hydrochar’s production involves hydrothermal carbonization, a nuanced process operating under moderate temperatures and pressures that transforms wet organic biomass into a solid carbonaceous product. This production route contrasts with traditional dry pyrolysis used to create biochar, thereby endowing hydrochar with a unique composition. Specifically, hydrochar embodies both labile carbon fractions capable of stimulating microbial activity and more recalcitrant carbon forms conducive to long-term persistence in soil matrices. This dual carbon nature underpins its ability to foster simultaneous soil fertility enhancement and carbon retention.

Empirical findings from the microcosm incubation experiments reveal that hydrochar application significantly elevates the proportion of macroaggregates—larger soil particles notable for their stability and protective effect on organic carbon against rapid mineralization. Moreover, hydrochar boosts mean weight diameter, a key indicator of aggregate stability, alongside measurable increases in soil organic carbon content relative to untreated controls. Notably, hydrochar sourced from Zanthoxylum stalks emerges as especially potent, exhibiting heightened carbon retention and exerting substantial improvements on soil aggregation metrics.

Unraveling the mechanisms behind hydrochar’s effectiveness, researchers underscore that the observed benefits extend beyond mere carbon content. The interplay of dissolved organic carbon, enhanced microbial activity, the presence of lignin-derived compounds, and the equilibrium between labile and recalcitrant carbon pools collectively orchestrate soil improvements. Intriguingly, hydrochar-origin carbon predominantly accumulates as particulate organic matter integrated within macroaggregates, suggesting that soil structural protection plays an instrumental role in stabilizing newly introduced carbon and mitigating its decomposition.

The study also highlights that hydrochar’s agronomic utility is intricately linked to its feedstock origin. Hydrochars derived from pig manure supply a richer nutrient profile and stimulate microbial biomass carbon, aligning with objectives centered on fertility enhancement. In contrast, lignocellulosic stalk-based hydrochars excel in safeguarding carbon stocks and reinforcing soil structure, thereby supporting strategies focused on long-term carbon sequestration and aggregate stability. This feedstock-specific functionality advocates for strategic customization of hydrochar production tailored to diverse agricultural goals.

Authors Ran Xiao and Xiaoxuan Su emphasize this nuanced approach, noting the critical importance of selecting feedstocks that optimize soil amendment outcomes depending on specific soil management priorities. Their insights pioneer a more adaptive framework for utilizing agricultural and livestock residues, transforming what is often considered waste into high-value, multifunctional soil amendments that simultaneously address fertilizer needs, structural challenges, and climate mitigation targets.

This research signifies an actionable pathway for advancing sustainable agriculture by leveraging hydrochar as a dual-function amendment. Transforming residues into hydrochar not only enriches soil quality but also contributes meaningfully to carbon management imperatives by stabilizing organic matter and fostering resilient soil ecosystems. While these results arise from controlled microcosm studies, the mechanistic clarity achieved sets the stage for comprehensive field trials that could validate and refine hydrochar application protocols in diverse agronomic contexts.

Ultimately, this study positions hydrochar as a pioneering agent in climate-smart soil stewardship, offering customizable solutions that enhance cropland carbon storage while simultaneously fortifying soil physical properties. As agricultural sectors grapple with the challenges of sustaining productivity under the pressures of climate change and soil degradation, hydrochar may emerge as a vital tool to reconcile productivity with environmental sustainability—ushering in a new era of precision soil amendment science grounded in both ecological and economic benefits.

With growing awareness around soil health’s vital role in global food security and carbon cycling, hydrochar’s dual capacity to repair degraded soils and sequester carbon resonates strongly with contemporary environmental priorities. Future research and deployment strategies will likely explore optimizing hydrochar feedstock blends, production parameters, and application rates to maximize benefits across varied land uses, thus amplifying its impact as a cornerstone of regenerative agriculture and carbon-smart land management.

As this field advances, transparent collaboration between scientists, agricultural stakeholders, and policymakers will be essential to translate hydrochar research into scalable soil management innovations. By capitalizing on hydrochar’s unique properties, there lies an unprecedented opportunity to transform agricultural waste streams into ecological assets, thereby contributing decisively to efforts in combating soil degradation, enhancing food security, and mitigating climate change simultaneously.

Subject of Research: Experimental evaluation of hydrochar’s effect on soil aggregation and carbon sequestration.

Article Title: Hydrochar as an effective amendment for enhancing soil aggregation and carbon sequestration: evidence from comparative microcosm experiments.

News Publication Date: 4-Mar-2026

Web References:

• Journal Biochar: https://link.springer.com/journal/42773
• DOI: http://dx.doi.org/10.1007/s42773-025-00547-y

References:
Sun, L., Wang, J.J., Wei, S. et al. Hydrochar as an effective amendment for enhancing soil aggregation and carbon sequestration: evidence from comparative microcosm experiments. Biochar 8, 69 (2026). https://doi.org/10.1007/s42773-025-00547-y

Image Credits: Liyang Sun, Jim J. Wang, Sun Wei, Pingping Ye, Yue Deng, Xiangtian Meng, Ronghua Li, Zongsheng Zhang, Xiaoxuan Su & Ran Xiao

Keywords

Soil aggregation, carbon sequestration, hydrochar, soil organic carbon, soil structure, hydrothermal carbonization, biochar, soil fertility, carbon-rich amendments, climate-smart agriculture, purple soil, particulate organic matter