Sorghum–Soybean Intercropping for Yield Benefit: A Systematic Review and Exploratory Meta-Analysis

Sorghum (Sorghum bicolor L.)–soybean (Glycine max L.) intercropping produces a significant yield advantage over monocropping. However, a comprehensive synthesis is lacking to quantify yield benefits. This article provides a systematic review, a primary meta-analysis, and an exploratory meta-analysis to quantify the land productivity advantage of sorghum–soybean intercropping, explore the impact of planting configuration, and critically assess the methodological robustness of the existing literature. A random-effect meta-analysis of Land Equivalent Ratio (LER), with a primary analysis on studies with reported and calculated variance only (n = 23 treatments from six studies) and an exploratory analysis on the full dataset, which includes studies with imputed variances (n = 103 treatments from 21 studies). Group-specific analyses examined row configurations. The exploratory meta-analysis showed a pooled LER of 1.31 (95% CI: 1.25–1.36), suggesting an approximately 31% average land productivity gain (LER > 1). Configuration beyond a 1:1 row ratio showed potential for higher yield gains (LER = 1.43 for 2:2). Critically, over 75% of studies required variance data imputation. The analysis, limited to studies with reported or calculated variance data, showed a higher LER of 1.55 (95% CI: 1.41–1.69), but with extreme heterogeneity (I2 = 96.2%). This highlights substantial outcome variability and inconsistent statistical reporting in the literature, limiting robust synthesis. Future research must prioritize long-term, well-replicated experiments with reported standardized variance and configuration evaluations to enable precise, locally relevant intercropping recommendations.