Effects of organic fertilizers on soil fertility and plant nutrition in agricultural crops

Intensive cropping based on mineral fertilizers has depleted soil organic matter in many regions, renewing interest in organic fertilizers (animal manures, composts, vermicomposts, digestates, humic-based and bio-organic products). This narrative review synthesizes 30 peer-reviewed sources, prioritizing meta-analyses, long-term field experiments and reviews, to evaluate how organic fertilizers affect soil physical, chemical and biological fertility and plant nutrition. Across studies, organic inputs consistently raise soil organic carbon (on average about 35% in a manure meta-analysis of 101 studies) and microbial biomass (roughly 36–40% above mineral-fertilized soils), and improve aggregate stability and bulk density. Nutrient release is slower and less synchronized with crop demand than from mineral fertilizers, so yield responses depend on rate, source, soil and duration. Partial substitution of mineral N (about 40–60%) typically maintains or slightly raises cereal yields and N use efficiency, while in vegetables such as tomato organic and bio-organic products often improve fruit quality. Organic-only systems generally show a yield gap of about 20–25%, which narrows with diversification. Risks include salt accumulation, trace elements, veterinary antibiotics and variable disease suppression. Evidence remains geographically biased and short on arid, saline soils. Integrated nutrient management, rather than full replacement, emerges as the best-supported strategy.

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