Spårelement i Sveriges jordbruksmark : flöden, trender och fältbalanser

Abstract: Field balances based on supply and removal of trace elements from the topsoil have been calculatedfor farms specialized in crop, dairy and pig production in Sweden. Today's field balances have beencompared with the field balances of 1990 in order to examine if, and then how, the situation haschanged. 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 % forHg and with 2 % for Pb in 100 years. There is today balance between supply and removal of the traceelements As, Cd, Cr, Mn and Ni. In the south of Sweden, on crop farms with sugar beets in the croprotation, one can see a decrease in the concentration of Cd in the top soil by -6 % over a period of100 years. The reason is that this crop contains a relatively high concentration of Cd that is beingremoved through harvest. However, it is not unusual that sugar beet residues are returned to thefields directly or through animal feed in which much of this Cd are brought back to the soil. Part ofthis 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 mineralfeed. It has been calculated that the concentration of these trace elements will increase in the topsoilwith 27 % and 32 % on dairy farms and increase with 36 % each on pig farms on an average over aperiod of 100 years. The rate of change for Hg on pig farms and for Cd, Hg and Mn on milk farms are3.5 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 inthis range on pig farms. These rates of change are small and indicate that there is a balance betweensupply and removal for several of these trace elements.Regardless of farming system, the net flow for the majority of trace elements has declined comparedto 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 allthree examined farming systems deposition still contributes most to the accumulation of the nondesirabletrace elements Cd, Hg and Pb. In order to decrease the rate of accumulation of these traceelements it is therefore urgent with a further reduction of the deposition. Concentrations of Cu andZn in the topsoil on crop farms are decreasing faster today than in 1990, which in the future may leadto the need for an additional supply through fertilization. On dairy and pig farms there is a significantincrease in the accumulation of these trace elements which might lead to problems with excessivelevels in the topsoil.