Status of heavy metals, nutrients, and total salts in commercial organic fertilizers and organic wastes in China

Objectives Heavy metals, nutrients, and EC (electrical conductivity) in commercial organic fertilizers and organic wastes in main vegetable production regions of China were evaluated to provide a scientific basis for high-efficiency and safe vegetable fertilizer recommendation, and soil quality improvement.

Methods About 126 representative samples of commercial organic fertilizers and 255 samples of organic wastes were collected from the main vegetable production regions, including 6 provinces (municipalities) of northern China and 12 provinces (municipalities) of southern China. The sampling periods were in early January of 2014, and status of heavy metals, nutrients, and EC in three types of commercial organic fertilizers and five types of organic wastes were investigated in this study.

Results 1) According to the China NY525-2012 maximum limits for heavy metals in commercial organic fertilizers, the percentage of the samples exceeding the limitation was respectively 10.3% for Cd, 17.2% for Pb and 17.2% for Cr in commercial chicken fertilizers, 20.0% for Cd and 6.7% for As in commercial pig fertilizers, 13.4% for Cr, 2.4% for Cd, 2.4% for As and 2.4% for Hg in other commercial organic fertilizers, 2.4% for Cd, 7.1% for As and 2.4% for Hg in chicken manures, 1.5% for Cd, 3.1% for Pb, 15.4% for As and 1.5% for Hg in pig manures, 1.7% for Cd and 1.7% for Hg in cattle manures, 12.5% for Cd in sheep manures, and 4.5% for Cr and 13.6% for As in other organic manures. Present livestock and poultry dungs were greatly different with traditional organic fertilizers, and compared with the results investigated in 1990s especially, the contents of total Cu and total Zn in chicken and pig manures increased by 1.5-16.2 and 1.3-4.7 times, respectively. 2) The contents of N, K₂O, and total nutrients (N+P₂O₅+K₂O) in commercial organic fertilizers were 51.2%, 32.0% and 15.0% higher than those in organic wastes, respectively, whereas the contents of P₂O₅and OM (organic matter), and ratios of C/N and C/P in organic wastes were 23.7%, 41.5%, 22.7% and 15.2% higher than those in commercial organic fertilizers. For commercial organic fertilizers, relatively higher values were found for the contents of P₂O₅and OM, and ratios of C/N in commercial pig fertilizers, and for the contents N, K₂O and total nutrients, and ratios of C/P in other commercial organic fertilizers. For organic wastes, relatively higher values were observed for the contents of N, P₂O₅and total nutrients in chicken and pig manures, for the contents of K₂O in chicken and sheep manures, and other organic manures, for the contents of OM in pig, cattle and sheep manures, for ratios of C/N in cattle manures, and for ratios of C/P in cattle and sheep manures. 3) EC values in commercial organic fertilizers (averaged 23.5 mS/cm, n=126) were 3.1 times as high as that in organic wastes (averaged 7.7 mS/cm, n=255). For commercial organic fertilizers, EC values were relatively higher in other commercial organic fertilizers, medium in commercial pig fertilizers, whereas relatively lower in commercial chicken fertilizers. For organic wastes, EC values were relatively higher in chicken manures and other organic manures, medium in sheep manures, whereas relatively lower in pig and cattle manures.

Conclusion The main heavy metals in the contents beyond the limitation were Cd, Pb and Cr in commercial chicken fertilizers, Cd and As in commercial pig fertilizers, Cr in other commercial organic fertilizers, As in pig manures, chicken manures and other organic manures, and Cd in sheep manures. The contents of N, K₂O, and total nutrients were respectively higher for commercial organic fertilizers compared with organic wastes, whereas the contents of P₂O₅and OM, and ratios of C/N and C/P were respectively higher for organic wastes compared with commercial organic fertilizers. EC values in commercial organic fertilizers were much higher than those in organic wastes.