Nitrogen transformations in copper-contaminated soils and effects of lime and compost application on soil resiliency

A neutral and an acidic soil were treated with different doses (0-3,000 mg Cu kg(-1) soil as CuSO4) of copper. The percentages of inhibition of nitrif ication in both soils varied from 5 to 97%, but for the N mineralization th ese percentages varied from 8 to 65%. The toxic effect of Cu for basal nitr ification and N mineralization was assessed as critical. Nitrification was more sensitive than ammonification to copper toxicity. It appears that an e cological dose of inhibition for nitrification and N mineralization higher than 10% is suitable as an indicator for Cu contamination. Soil resiliency assessed by N mineralization in the lime treatments varied from 11 to 154% in the sandy soil and from 70 to 168% in the sandy loam soil. A combined ap plication of lime and compost significantly increased soil resiliency. The percentage increase varied from 904 to 1,390% in the sandy soil and from 76 7 to 2,230% in the sandy loam soil. It appears that compost was a powerful agent for recovering the soil fertility of Cu-contaminated soils as assesse d by N transformation. The acidic sandy soil showed a lower capacity for re covery after Cu toxicity stress.