Evidence review · Soil & plants · Across studies
Across 81 studies, humic substances raised early plant growth on average, with wide variation.
On average, humic substances raised early plant growth by about a fifth, but the spread was wide: about half of the shoot studies found a gain of less than 5 percent.
Rose et al., 2014. Advances in Agronomy 124:37 to 89.
Scope, material and route
- Studied
- Multiple crop and plant species
- Design
- Random-effects meta-analysis of published experiments, with a narrative review
- Material
- Humic substances from brown coal (including leonardite), peat, soil, composts and manures
- Route
- Root, foliar, soil and combined applications
Study design
What was pooled
Selected from 390 papers retrieved.
81 papers57 reported shoot and 39 root dry weight; the two sets overlap, since some papers reported both.
- Over 700 data pointsEach a single comparison of a treated plant group with its own untreated control, so one paper can give many
Shoot dry weight
- Pooled responsePlus 22 ± 4 percent
- Influential outliers removedPlus 19 ± 3 percent
- SpreadAbout half of the shoot studies found a gain of less than 5 percent
Root dry weight
- Pooled responsePlus 21 ± 6 percent
- Influential outliers removedPlus 20 ± 4 percent
- SpreadAbout one third of the root studies found a gain of less than 5 percent
More study details
- Research question
- How large and how consistent is the plant growth response to humic substances, and which factors moderate it?
- Studies included
- 81 papers (57 reporting shoot and 39 reporting root dry weight), selected from 390 retrieved; over 700 data points
- Search
- Scopus and Web of Science; described by the authors as an unbiased selection rather than an exhaustive one
- Comparator
- Untreated controls within each included experiment
- Moderators tested
- Growth medium, stress level, plant type, source of humic substances, application site and rate
- Outcomes measured
- Shoot and root dry weight relative to control
Findings
This review pooled 81 published papers, over 700 data points, that reported shoot or root dry weight for plants treated with humic substances and for untreated controls. The pooled estimates were increases of 22 ± 4 percent in shoot dry weight and 21 ± 6 percent in root dry weight, or 19 ± 3 and 20 ± 4 percent after influential outliers were removed. The spread was wide: about half of shoot studies and a third of root studies found less than a 5 percent gain. The source of the material and plant stress changed the response, and peat and brown coal materials did not affect root growth. Most included studies measured early growth, not yield in the field.
| Outcome | Comparison or result | Interpretation |
|---|---|---|
| Shoot dry weight | Plus 22 ± 4 percent; plus 19 ± 3 percent after removing influential outliers | An average across very different experiments |
| Root dry weight | Plus 21 ± 6 percent; plus 20 ± 4 percent after removing outliers | An average across very different experiments |
| Consistency | About half of shoot studies and one third of root studies found less than a 5 percent gain | A meaningful share of experiments showed little or no benefit |
| Source of material (shoot) | Peat 4 ± 12 percent (not significant); brown coal 12 ± 4; green waste and manure composts 28 to 29; soil 25 | Material identity changes the response |
| Plant stress (shoot) | 28 ± 6 percent under high stress compared with 18 ± 3 percent without stress | Conditions change the response |
| Woody perennials | No significant promotion; lower biomass than controls in three studies at high rates | Not all plant groups responded |
| Publication bias | Not detected by funnel plot or regression tests | Within the limits of these tests |
Interpretation and limits
What this record supports
That humic substances often increase early plant growth in experiments, that the effect varies widely, and that source material and growing conditions matter.
What remains uncertain
- Field yield. Few included studies followed crops to maturity under statistically rigorous field conditions.
- Assumed variance. Where a study did not report a standard error, the authors assumed 10 percent of the mean.
- Reporting. The ± values on the pooled estimates are not defined in the text; the figures show 95 percent confidence intervals.
- Prediction. A pooled average does not predict the response of a particular product, crop or soil.
Which part of the framework it informs
Environmental conditions
The physical, chemical and management context.
Microbial activity
What microbial communities do within that context.
Observable function
What can be observed or measured in the host or wider system.
This record informs this area.
Source, funding and review
- Source type
- Peer-reviewed publication
- Associated products
- This record does not assess an associated product.
- Funding and relationships
- Funders listed in the paper include coal-sector research bodies. The review did not test a commercial product.
- Review status
- Prepared as an editorial summary. External scientific review has not been completed.
- What was read
- Accepted manuscript read in full from a university repository; the publisher's page blocks automated access.
- Original title
- A meta-analysis and review of plant-growth response to humic substances: practical implications for agriculture
- Authors
- Rose MT, Patti AF, Little KR, Brown AL, Jackson WR, Cavagnaro TR
- Publication
- Advances in Agronomy 124:37 to 89, 2014
- DOI
- 10.1016/B978-0-12-800138-7.00002-4
- Summary prepared by
- Carbon Biome Project
- Date added
- 19 October 2026
- Cite this summary
- Carbon Biome Project. Across 81 studies, humic substances raised early plant growth on average, with wide variation. Evidence library record, added 19 October 2026. carbonbiomeproject.com/evidence/rose-2014-meta-analysis-plant-growth-humic-substances/
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