COMPARABILITY OF MICROCOSM AND FIELD STUDIES IN ASSESSING NITROGEN-FIXING BACTERIA'S IMPACT ON CROP YIELD: A META-ANALYSIS

Crop inoculation with nitrogen-fixing bacteria (NFB) is a promising strategy for sustainable agriculture, but its effectiveness has been assessed using both field and microcosm studies, raising questions about the translatability of results.To address this, we conducted a comprehensive weighted meta-analysis of 78 studies (410 observations) across five major crops-wheat (Triticum aestivum L.), rice (Oryza sativa), maize (Zea mays L.), chickpea (Cicer arietinum L.), and barley (Hordeum vulgare)-to compare yield outcomes from NFB inoculation in both study types.Our analysis revealed that NFB inoculation had a significantly positive effect on crop yield (Hedges' g = 1.05).While there was no significant difference in the mean effect size between the field and microcosm studies (P = 0.326), we found that soil inoculation provided a significantly larger yield enhancement than seed inoculation (P = 0.011).Crucially, a metaregression of microcosm studies showed that experimental design parameters such as soil volume and plant density significantly influenced the magnitude of the NFB effect (P 0.006).Although microcosm studies can produce results directly comparable to those from the field, they exhibit greater variability, and their outcomes are highly sensitive to experimental design.These findings underscore the utility of microcosms as models while highlighting the need for caution and careful design when extrapolating their results to field conditions.