Comparative Analysis of Commercial Organic Fertilizers Revealing Elevated Nutrient and Contaminant Loads in Pig Manure-Based Fertilizer

Organic fertilizers are rich in nutrients but also frequently contain multiple contaminants that pose a potential threat to the agricultural environment. However, comprehensive investigations into commercial organic fertilizers remain scarce. In this study, 54 commercial organic fertilizer samples—including animal manure-based fertilizers, BOF (bio-organic fertilizer), and other types of fertilizers—were systematically investigated. For OM (organic matter), 48.15% of samples fell below the 30% w/w threshold specified by the industry standard NY/T 525-2021. The exceedance rates of Cu and Zn across all fertilizers were 14.81% and 12.96%, respectively, relative to the German Biowaste Ordinance (BioAbfV) limits. Differences in properties among geographic origins were less pronounced than those among fertilizer types. Pig manure-based fertilizers had the highest nutrient contents, especially phosphorus, but also the highest levels of contaminants, including antibiotics, heavy metals, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARGs). BOF exhibited the best overall quality, with a total nitrogen content 2.0–4.4 times that of the manure-based fertilizers, together with higher organic matter and lower contaminant levels. This study establishes a comprehensive baseline for commercial organic fertilizers in China, providing critical empirical evidence for future industry governance and fertilizer management.