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.