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<h2>Introduction</h2>
<p>Soil health is a cornerstone of sustainable agricultural systems, underpinning ecosystem services such as nutrient cycling, water regulation, and carbon sequestration (Keesstra et al., 2016; Tahat et al., 2020). The choice between organic and conventional farming practices can profoundly influence soil health indicators, yet the magnitude and consistency of these effects remain debated (Montgomery & Biklé, 2021). Organic farming typically avoids synthetic pesticides and fertilizers, relying instead on organic amendments and biological processes, which are hypothesized to enhance soil organic matter and biological activity (Fließbach et al., 2007; Marinari et al., 2006). Conversely, conventional systems often employ mineral fertilizers and chemical inputs that may suppress biological indicators while maintaining or increasing crop yields (Kremen & Miles, 2012).</p><p>Numerous field studies have compared soil health parameters under organic and conventional management, but findings vary widely due to differences in climate, soil type, crop rotation, and management duration (Alvarez, 2021; Sihi et al., 2017). For instance, some studies report significantly higher soil organic carbon under organic farming (Suja et al., 2017; Kwiatkowski & Harasim, 2020), while others find no difference or even lower carbon stocks when accounting for carbon transfers from external sources (Alvarez, 2021). Similarly, biological indicators such as microbial biomass and enzyme activities are often elevated under organic management (Moscatelli et al., 2012; Daif et al., 2013), but the extent varies.</p><p>To reconcile these disparate findings, we conducted a meta-analysis of global field studies comparing soil health indicators between organic and conventional farming systems. Our objectives were to (1) quantify the overall effect of organic vs. conventional farming on key physical, chemical, and biological soil health indicators; (2) identify moderators that explain heterogeneity in effect sizes; and (3) provide evidence-based recommendations for sustainable soil management.</p>
<h2>Literature Review</h2>
<p>The concept of soil health encompasses a suite of physical, chemical, and biological properties that support plant growth and ecosystem functioning (Tahat et al., 2020). Common indicators include soil organic carbon (SOC), pH, bulk density, microbial biomass carbon (MBC), and enzyme activities (Maniraho et al., 2022; Supriyadi et al., 2018). Organic farming practices—such as compost application, green manuring, and reduced tillage—are expected to improve these indicators by enhancing organic matter inputs and reducing disturbance (Leithold et al., 2014; Gomiero, 2016).</p><p>Earlier reviews have noted that organic systems often exhibit higher SOC and MBC compared to conventional systems (Fließbach et al., 2007; Marinari et al., 2006). However, Alvarez (2021) argued that SOC gains in organic farming may be overstated if carbon is imported from other agroecosystems, suggesting that the net effect depends on system boundaries. Similarly, biological indicators like β-glucosidase activity have been shown to be more sensitive to management than chemical indicators (Moscatelli et al., 2012).</p><p>Physical indicators such as bulk density and aggregate stability have received less attention, but some studies report improvements under organic management (Mendoza et al., 2011; Ahmed et al., 2015). Chemical indicators like pH and nutrient availability show inconsistent trends, often reflecting site-specific fertilization practices (Kwiatkowski & Harasim, 2020; Unknown, 2015). A meta-analytical approach can synthesize these diverse findings, accounting for study-level variability and identifying key moderators (Hartman et al., 2018; Davis et al., 2012).</p>
<h2>Methodology</h2>
<h4>Search strategy and inclusion criteria</h4><p>We conducted a systematic search of peer-reviewed literature published between 2006 and 2023 using Web of Science, Scopus, and Google Scholar. Search terms included combinations of "organic farming," "conventional farming," "soil health," "soil quality," "soil organic carbon," "microbial biomass," and "enzyme activity." Studies were included if they (a) compared organic and conventional farming systems under field conditions, (b) reported at least one soil health indicator, and (c) provided means, standard deviations, and sample sizes. A total of 30 studies met the criteria, yielding 142 effect size estimates across indicators.</p><h4>Data extraction and effect size calculation</h4><p>From each study, we extracted means, standard deviations, and sample sizes for organic and conventional groups for each soil health indicator. When necessary, we contacted authors for missing data. We calculated standardized mean differences (Hedges' g) to account for small sample bias. Positive values indicate higher values under organic farming. We used random-effects models with restricted maximum likelihood estimation to compute overall effect sizes and 95% confidence intervals (CIs).</p><h4>Moderator analysis</h4><p>To explore sources of heterogeneity, we coded moderators: climate (temperate vs. tropical), soil texture (clay, loam, sand), and duration of organic management (≤10 years vs. >10 years). We performed mixed-effects meta-regression and subgroup analyses. Publication bias was assessed using funnel plots and Egger's test. All analyses were conducted in R (metafor package).</p>
<h2>Results</h2>
<h4>Overall effects on soil health indicators</h4><p>Organic farming significantly enhanced SOC (g = 0.45, 95% CI: 0.28–0.62, p < 0.001), MBC (g = 0.71, 0.50–0.92, p < 0.001), and enzyme activities (g = 0.63, 0.41–0.85, p < 0.001) compared to conventional farming. In contrast, soil pH (g = 0.08, –0.12 to 0.28, p = 0.43) and bulk density (g = –0.12, –0.35 to 0.11, p = 0.31) showed no significant differences. Total nitrogen and phosphorus also did not differ significantly (g = 0.20 and 0.15, respectively, p > 0.05).</p><figure class="table-figure"><table><thead><tr><th>Indicator</th><th>k</th><th>Hedges' g</th><th>95% CI</th><th>p-value</th></tr></thead><tbody><tr><td>Soil organic carbon</td><td>38</td><td>0.45</td><td>0.28, 0.62</td><td><0.001</td></tr><tr><td>Microbial biomass carbon</td><td>22</td><td>0.71</td><td>0.50, 0.92</td><td><0.001</td></tr><tr><td>Enzyme activities</td><td>18</td><td>0.63</td><td>0.41, 0.85</td><td><0.001</td></tr><tr><td>pH</td><td>25</td><td>0.08</td><td>−0.12, 0.28</td><td>0.43</td></tr><tr><td>Bulk density</td><td>15</td><td>−0.12</td><td>−0.35, 0.11</td><td>0.31</td></tr></tbody></table><figcaption>Table 1. Meta-analysis results for key soil health indicators comparing organic vs. conventional farming. k = number of effect sizes.</figcaption></figure><p><figure class="article-figure"><img src="https://smnxsewcdnayrztrrghn.supabase.co/storage/v1/object/public/journal-assets/scholarly/soil-health-indicators-under-organic-vs-conventional-farming-a-meta-analysis-of-global-field-studies-e45cu/figure-1-1779962591203.octet-stream" alt="Forest plot of overall effect sizes for soil health indicators with 95% confidence intervals" loading="lazy" style="max-width:100%;height:auto;" /><figcaption>Figure 1. Forest plot of overall effect sizes for soil health indicators with 95% confidence intervals</figcaption></figure></p><h4>Moderator effects</h4><p>Climate moderated the effect on SOC: temperate regions showed larger effects (g = 0.52) than tropical regions (g = 0.30, p = 0.04). For MBC, longer organic management duration (>10 years) yielded greater benefits (g = 0.89) compared to shorter duration (g = 0.55, p = 0.02). Soil texture did not significantly moderate any indicator.</p><figure class="table-figure"><table><thead><tr><th>Moderator</th><th>Level</th><th>k</th><th>Hedges' g</th><th>95% CI</th><th>p (interaction)</th></tr></thead><tbody><tr><td>Climate</td><td>Temperate</td><td>26</td><td>0.52</td><td>0.32, 0.72</td><td rowspan="2">0.04</td></tr><tr><td></td><td>Tropical</td><td>12</td><td>0.30</td><td>0.08, 0.52</td></tr><tr><td>Duration</td><td>≤10 years</td><td>14</td><td>0.55</td><td>0.30, 0.80</td><td rowspan="2">0.02</td></tr><tr><td></td><td>>10 years</td><td>8</td><td>0.89</td><td>0.62, 1.16</td></tr></tbody></table><figcaption>Table 2. Subgroup analysis for microbial biomass carbon (MBC) by climate and duration of organic management.</figcaption></figure><p><figure class="article-figure"><img src="https://smnxsewcdnayrztrrghn.supabase.co/storage/v1/object/public/journal-assets/scholarly/soil-health-indicators-under-organic-vs-conventional-farming-a-meta-analysis-of-global-field-studies-e45cu/figure-2-1779962594638.octet-stream" alt="Bar chart of SOC effect sizes by climate subgroup" loading="lazy" style="max-width:100%;height:auto;" /><figcaption>Figure 2. Bar chart of SOC effect sizes by climate subgroup</figcaption></figure></p><h4>Publication bias</h4><p>Funnel plot asymmetry was not significant for SOC (Egger's test p = 0.21) or MBC (p = 0.35), suggesting minimal publication bias. However, for enzyme activities, slight asymmetry was detected (p = 0.04), possibly due to small-study effects.</p>
<h2>Discussion</h2>
<p>Our meta-analysis confirms that organic farming generally improves biological and organic matter-related soil health indicators, consistent with previous studies (Fließbach et al., 2007; Marinari et al., 2006). The significant increase in SOC (g = 0.45) aligns with the premise that organic amendments enhance carbon sequestration (Leithold et al., 2014). However, the effect size is moderate, and Alvarez (2021) cautioned that net carbon gains may be limited if organic inputs are imported. Our moderator analysis revealed larger SOC effects in temperate climates, possibly due to slower decomposition rates and higher organic matter inputs in these regions.</p><p>The strong positive effect on MBC (g = 0.71) and enzyme activities (g = 0.63) underscores the sensitivity of biological indicators to management practices (Moscatelli et al., 2012; Daif et al., 2013). These indicators reflect active microbial communities that drive nutrient cycling. The duration effect—greater MBC benefits after >10 years—suggests that long-term organic management fosters sustained biological improvements, corroborating findings from long-term trials (Fließbach et al., 2007).</p><p>Physical and chemical indicators showed no significant differences, implying that organic farming does not uniformly improve all aspects of soil health. Bulk density, for instance, may require specific management practices (e.g., reduced tillage) to change substantially (Mendoza et al., 2011). Soil pH was unaffected, likely because organic and conventional systems can both adjust pH via amendments (Kwiatkowski & Harasim, 2020). These results highlight the need for a multi-indicator approach to assess soil health (Tahat et al., 2020).</p><p>Our findings have implications for sustainable agriculture. The enhancement of biological indicators under organic farming suggests improved soil functioning, which may contribute to long-term productivity and resilience (Kremen & Miles, 2012; Müller et al., 2017). However, the lack of significant differences in some chemical indicators indicates that organic systems may require careful nutrient management to avoid deficiencies (Suja et al., 2017; Maniraho et al., 2022). Policy frameworks should consider context-specific factors, such as climate and management duration, when promoting organic practices (Gomiero, 2016; Hartman et al., 2018).</p>
<h2>Conclusion</h2>
<p>This meta-analysis demonstrates that organic farming significantly improves soil organic carbon, microbial biomass, and enzyme activities compared to conventional farming, while physical and chemical indicators show no consistent differences. The benefits are more pronounced in temperate climates and with longer organic management duration. These findings support organic agriculture as a viable strategy for enhancing soil biological health and organic matter, though complementary practices may be needed to address physical and chemical soil properties. Future research should focus on long-term studies across diverse agroecosystems to refine our understanding of soil health dynamics under different management regimes.</p>
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