Biochar, the carbon-rich solid produced by pyrolyzing biomass under limited-oxygen conditions, has become one of the most extensively studied soil amendments in modern agronomy, valued simultaneously for its potential to raise crop productivity, improve soil health, and durably sequester carbon. This review synthesizes peer-reviewed meta-analyses and global field-trial syntheses (2011-2026) covering biochar's effects on soil physical properties (water retention, bulk density), chemical properties (pH, cation exchange capacity, nutrient availability), biological properties (microbial biomass, enzyme activity, nitrogen cycling), crop yield, drought resilience, and heavy-metal remediation. Across major global meta-analyses, biochar alone raises crop yield by roughly 9-25% on average, with substantially larger effects in acidic, weathered, tropical soils than in fertile temperate soils, and the largest, most consistent gains occurring when biochar is co-applied with inorganic or organic fertilizer rather than used alone. Biochar reliably improves available water capacity in coarse-textured soils (up to +45-51%), raises cation exchange capacity and microbial biomass carbon, and can reduce cadmium bioavailability in contaminated acidic soils by 41-70%. These benefits are not unconditional: excessive application rates, freshly produced (unaged) biochar, and use on already-fertile fine-textured soils can each produce neutral or negative yield effects, chiefly through temporary nitrogen immobilization or nutrient imbalance. We conclude that biochar functions best as a soil-specific, rate-calibrated amendment integrated with existing fertilization programs rather than a universal input, with the strongest agronomic and economic case in degraded, acidic, or sandy soils in tropical and subtropical smallholder systems.