Die Bodenkultur - Journal for Land Management, Food and Environment
T. Kickinger, H. Würzner and W. Windisch:
Zinc and copper in feeds, slurry and soils from Austrian pig fattening farms feeding commercial complete feed or feed mixtures produced on-farm
Dung from pig production (breeding as well as fattening) has been repeatedly reported to contain high amounts of Zn and Cu compared to dung from cattle and poultry, presumably due to abundant application of excessive Zn and Cu in feeds. This gives raise to the assumption that Zn and Cu in pig dung is significantly lower if such practices are not applied. Therefore, the present model study assessed 27 Austrian pig fattening farms as a model to pig production. Zn and Cu in feeds and slurry were monitored, as well as in soils from each 3 farms with lowest and highest slurry Zn, respectively. Six of selected farms used commercial compound feed (CCF) as only feed source, while 21 farms fed feed mixtures produced on-farm (FMF) In CCF-type farms, the amounts of Zn and Cu entering the fattening units via feeds and the corresponding efflux into the slurry stores were quantitatively recorded.
Within FMF-type farms, 2 datasets for Zn and 3 for Cu were withdrawn from further evaluation due to unusually high contents in feeds and slurry (probably reflecting dietary Zn and/or Cu excess). Feed from CCF-type farms contained 104 ± 26 mg Zn/kg and 20 ± 2 mg Cu/kg (based on 88 % dry matter (DM)) and matched the limits given by feed law. Respective values for FMF-type farms were 25 % higher (129 ± 39 and 25 ± 6) and partially exceeded legal limits. Corresponding mean concentrations on Zn and Cu in slurry (mg/kg DM) were 522 ± 194 and 105 ± 35 for CCF-type farms, but higher in FMF-type farms (695 ± 295 and 154 ± 55). For CCF-type farms, transfer rate from feed into slurry accounted for 84 ± 11 % (Zn) and 69 ± 6 % (Cu). Soil Zn and Cu (mg/kg DM) from farms with lowest slurry Zn (only CCF-type farms) averaged 72 ± 11 and 23 ± 6, while farms with highest slurry Zn (FMF-type farms only) exhibited numerically higher levels (78 ± 16 and 25 ± 5). The correlation between slurry and soil Zn was r = 0.70 (p < 0.11).
The observations of this study suggest that Zn and Cu in feeds are the dominant factors affecting respective concentrations in pig dung. If Zn and Cu is fed according to limits set by feed law without using dietary excess (e.g. Cu to piglets), Zn and Cu concentrations in pig dung may be expected to be significantly lower than previously reported. This would counteract accumulation of Zn and Cu in soils.
Key words: Zn, Cu, feed, slurry, soil.