Fig. 3. Average total N concentration profiles. Comparison between control and organic layer columns. Nitrate and nitrite N values were averaged over the sampling period of October 2001–July 2002 (11–21 samples). Ammonia N values were averaged from March–July 2002 (5 samples) and organic N values were averaged from April–July 2002 (4 samples). Synthetic wastewater was applied from August 2001–August 2002.