Nitrogen Loss from a Soil Restored after Surface Mining

Anaerobic conditions develop below about 1‐m depth in soil stockpiles and this can lead to an accumulation of ammonium (NH+4) and transformations of a normally relatively inert organic‐N pool within the soil. After reinstatement of the soil from the stockpile, the NH+4 may rapidly be transformed to nitrate (NO−3) and lost from the soil with the labile organic‐N. These losses may lead to a pollution risk in addition to the loss of a resource. The magnitude of N losses were measured from a soil that had been reinstated for agricultural use after being stored in a stockpile for 12 yr. Nitrogen movement in the soil profile and losses into the water‐course were monitored for 2 yr beginning immediately after reinstatement. Relatively large movements of N were detected within the soil profile and large losses to the atmosphere and/or water‐courses were estimated. Over the 2‐yr monitoring period, 2449 kg ha−1 of N was lost from the soil profile; 90% of this was not accounted for either in the soil or in the runoff or drainage water as mineral‐N and was presumed to have entered either the atmosphere or aquatic environment as organic‐N. To aid remedial measures, the proportion entering the atmosphere as nitrogen and nitrous oxides or the aquatic environment as organic‐N, needs further investigation.