Contents of nutrient elements and pollutants in different sources of animal manures

Intensive confined livestock and poultry production systems generate large quantities of by-product that can be potentially recycled on lands as manure. Environmental protection is a major consideration for developing management practices that effectively use livestock manure as nutrient resource and soil conditioner in agricultural production. To date, most environmental problems associated with land applications of by-product manure have centered mainly on groundwater and/or surface water contamination by nitrogen and phosphorus nutrients. With increasing use of trace elements such as Cu in nutritional supplements and antibiotics in livestock medicines as feed additives in intensive livestock industries, manure application has become the main source of heavy metal (e.g., Cu, Zn and As) and antibiotic load in soils. By-product manure is applied in farmlands to supply primarily soil N and/or P, without regard to heavy metal pollution. The danger lies in accumulation of manure-borne metals and antibiotics, which threaten food safety and security. To reduce the risk of offsite contamination, it is important to characterize the contents of nutrient elements and pollutants in animal manure. In this study, 155 samples of animal manure (including 93 samples of pig manure, 31 samples of chicken manure, 18 samples of duck manure and 13 samples of cow manure) were collected from both intensive animal farms and household animal houses in different regions of Zhejiang Province. Chemical and spectrum analysis were used to characterize the contents of nutrient elements, heavy metals and antibiotic residues. The results showed low contents of Cd, Cr, Hg, Ni and Pb and high contents of Cu and Zn in animal manure. The ranges of manure contents of Cu, Zn and As were 18.56~1 788.04 mg·kg^-1, 12.46~10 056.68 mg·kg^-1 and 0.69~76.43 mg·kg^-1, with mean values of 525.38 mg·kg^-1, 897.14 mg·kg^-1 and 10.01 mg·kg^-1, respectively. Based on the national standards of heavy metal load limit of sludge for land application (GB4284—84), percent samples of animal manure with Cu, Zn and As exceeding the standard limit were 53.55%, 43.87% and 0.65%, respectively. Residual levels of tetracycline (TC), oxytetmcyline (OTC) and chloroteracycline (CTC) in the manure varied from zero to 16.75 mg·kg^-1, 29.60 mg·kg^-1 and 11.63 mg·kg^-1, with mean values of 2.01 mg·kg^-1, 5.10 mg·kg^-1 and 2.17 mg·kg^-1, respectively. Percent samples of manure with TC, OTC and CTC were 61.29%, 72.90% and 69.03%, respectively. The ranges of N, P and K in the manure were 9.80~43.60 g·kg^-1, 7.98~54.30 g·kg^-1 and 8.76~35.20 g·kg^-1, with mean values of 23.63 g·kg^-1, 24.81 g·kg^-1 and 20.72 g·kg^-1, respectively. Manure P to N ratio range was 0.40~2.98, with a mean of 1.08. P, K, Cu, Zn and As contents as well as those of selected antibiotic residues were generally higher in on-farm animal manure than in household animal manure. These variables were also higher in pig manure than in the manure from other animals. Given the high Cu, Zn and antibiotic amounts of on-farm animal manure, its farm application should be controlled by adopting pretreatment measures that reduces residual antbiotic, Cu and Zn loads.