Formation of mineral N (NH4+, NO3-) during mineralization of organic matter from coal refuse material and municipal sludge

In 1994, the 14 hectare plateau of a coal refuse bank in Landsweiler-Reden (Southwest-Germany) was covered with a mixture consisting of 80% (v/v) refu se materials, 10% (v/v) composted wood and 10% (v/v) of sewage sludge as pa rt of a reclamation project. The amount of sludge dry matter applied was ap proximately 450 Mg ha(-1) to a depth of 2 m. The approximate amount of nitr ogen (N) applied with the substrate was 20 Mg ha(-1) (total N). From April 1996 until November 1997, contents of mineral nitrogen and nitrogen mineral ization were monitored down to a depth of 2 m. Nitrogen mineralization was monitored by means of a modified buried bag procedure using a retrievable c ylindrical receptacle. The contents of NH4+- and NO3--N were largest at the beginning of the obser vation period, reaching a peak value of 650 kg ha(-1) in May 1996. Then, mi neral N stabilized in 1997 at a level of 200 kg N ha(-1), with the soil pro file below 150 cm contributing about 75% to this amount. Net nitrogen miner alization was characterized by the same depth distribution. Other than in s urface horizons, mineralization activity at the bottom of the profile conti nued into 1997 with the same intensity as in 1996. Variability among replic ate buried bag incubations was high (CV > 100% on several occasions). Nitro gen loss through leaching was estimated at 630 kg N ha(-1) over the observa tion period, averaging at 360 kg N ha(-1) a(-1) The reclamation procedure u sed in this study may have the potential to contaminate ground water in hyd rologically sensitive areas.