Increased nitrogen leaching under piles of slash— a consequence of modern forest harvesting techniques

Piles of logging residues (slash‐piles) are a consequence of modem logging techniques. The piles cover 10 to 15% of a clear‐felled area. The effect of slash‐piles on nitrogen leaching was estimated by collecting precipitation¹ and percolating water below slash‐piles and below the O, E and B horizons of an Orthic Podzol during two growing seasons. Open funnels were used for precipitation, PVC troughs for water leaving the pile and filled‐in zero tension lysimeters for percolating soil water. Exchangeable ammonium and nitrate of humus samples were analysed. The increased nitrogen leaching from the soil below slash‐piles was probably caused by an increased mineralization of the humus layer and a reduced nitrogen uptake by roots.