Global-scale meta-analysis reveals enhanced cereal yields through sulfur and zinc fertilization

Crop yield response to secondary nutrient sulfur (S) and micronutrient zinc (Zn) has been extensively studied, yet inconsistent results and a lack of context-specific guidelines limit widespread adoption. We conducted a meta-analysis of 152 data points from 27 studies to quantify the impact of S and Zn separately and in combination on maize, rice, and wheat grain yields. Using standard mean difference (SMD) as the effect size metric, S and Zn application significantly improved yields across all crops (SMD = 1.043, 95% confidence interval: 0.891–1.194, p < 0.001), with no significant differences among species. The greatest yield gain was observed under S + Zn (SMD = 1.797), especially without nitrogen (SMD = 2.115), while co-application with N had no significant effect (SMD = 0.614). Yield was 8.55% higher with single-dose versus split application, though not statistically significant. Early and mid-season application (SMD = 1.245) outperformed three-stage application (SMD = 0.465). Zinc sulfate (SMD = 1.036) and ammonium sulfate (SMD = 2.173) were the most effective Zn and S sources, respectively. Yield responses were stronger on medium- and coarse-textured soils and under hot climates. While the highest yield gain was generally observed under S + Zn application without nitrogen, this outcome may reflect specific experimental conditions rather than a universally optimal strategy. These results identify global trends in yield responses to S and Zn and underscore the importance of soil, climate, nutrient combinations, and timing. However, because most studies were conducted under nutrient deficient conditions, yield gains under more fertile or less responsive conditions could be overestimated. Keywords Micronutrients ・ Secondary nutrients ・ Cereal yield ・ Soil types ・ Climatic conditions ・ Crop species