Epsilon Archive for Student Projects

Abstract

Field balances based on supply and removal of trace elements from the topsoil have been calculated
for farms specialized in crop, dairy and pig production in Sweden. Today's field balances have been
compared with the field balances of 1990 in order to examine if, and then how, the situation has
changed. Studied trace elements are arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu),
mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn).

The balance calculations show that the stores of Cu and Zn are depleted with an average rate of -15
% and -6 % over a 100-years period on crop farms when only commercial fertilizers are being used.
The concentrations of Hg and Pb tend to increase in the topsoil on crop farms with more than 3 % for
Hg and with 2 % for Pb in 100 years. There is today balance between supply and removal of the trace
elements As, Cd, Cr, Mn and Ni. In the south of Sweden, on crop farms with sugar beets in the crop
rotation, one can see a decrease in the concentration of Cd in the top soil by -6 % over a period of
100 years. The reason is that this crop contains a relatively high concentration of Cd that is being
removed through harvest. However, it is not unusual that sugar beet residues are returned to the
fields directly or through animal feed in which much of this Cd are brought back to the soil. Part of
this return is indirectly reflected in the balances of livestock farms.

On dairy and pig farms there is a considerable increase of the amounts of Cu and Zn in the topsoil.
Both elements occur in large quantities in manure as a consequence of being constituents of mineral
feed. It has been calculated that the concentration of these trace elements will increase in the topsoil
with 27 % and 32 % on dairy farms and increase with 36 % each on pig farms on an average over a
period of 100 years. The rate of change for Hg on pig farms and for Cd, Hg and Mn on milk farms are
3.5 to 5 % which indicates that concentrations probably increase gradually in the topsoil.
Concentrations of As, Cr, Ni and Pb are increasing in the topsoil on dairy and pig farms with up to 2.5
% on an average over a period of 100 years. The concentrations of Cd and Mn are also increasing in
this range on pig farms. These rates of change are small and indicate that there is a balance between
supply and removal for several of these trace elements.

Regardless of farming system, the net flow for the majority of trace elements has declined compared
to 1990. The rate of change in the topsoil has fallen to negligible levels for the trace elements As, Cd,
Cr, Hg, Mn, Ni and Pb. This depends, above all, on a lowered atmospheric deposition. However, in all
three examined farming systems deposition still contributes most to the accumulation of the nondesirable
trace elements Cd, Hg and Pb. In order to decrease the rate of accumulation of these trace
elements it is therefore urgent with a further reduction of the deposition. Concentrations of Cu and
Zn in the topsoil on crop farms are decreasing faster today than in 1990, which in the future may lead
to the need for an additional supply through fertilization. On dairy and pig farms there is a significant
increase in the accumulation of these trace elements which might lead to problems with excessive
levels in the topsoil.