Cattle and pig manure contain useful mineral nutrients (N, P, and K) and are therefore used
as organic fertilizer. However, excessive applications of manure can cause environmental problems
and threaten animal and human health because these materials also hold significant amounts of
heavy metals, particularly Cu and Zn. To assess the potential risk due to the increased concentrations
of heavy metals (Cu, Mn, Zn, and Cr) in a harvested crop, two maize hybrids were grown in pots on
four different soils with three different fertilisers (urea, pig manure, and cattle manure). Both soil
and manure characteristics influenced the heavy metal concentrations in the plant shoots. Organic
fertilisation strongly interacted with the soils and, in general, reduced the shoot content of Cu, Mn,
and Zn. A preliminary assessment of the heavy metal balance of the agricultural systems based on
the intensive livestock production and maize cultivation showed that the potential soil enrichment of
the long-term application of livestock manure arises mainly from the application of pig slurries that
have a high content of Cu and Zn. The time required to apply an amount of metal that is equal to the
initial soil content is 60\u2013300 years for Zn and 240\u2013450 years for Cu, depending on the soil type and
the initial heavy metal content
