NUTRIENT LOSSES AFTER CLEARFELLING IN BEDDGELERT FOREST - A COMPARISON OF THE EFFECTS OF CONVENTIONAL AND WHOLE-TREE HARVEST ON SOIL-WATER CHEMISTRY

The effects of conventional, bole only harvesting (CH) and whole-tree harvesting (WTH) on major inorganic nutrient concentrations (K, NO3-N, NH4-N, PO4-P and Ca) in soil water are described from Beddgelert fore st in North Wales. Monitoring of nutrient leaching losses, and the tim ing thereof, from brash through the soil and into streams draining the CH areas allowed assessments to be made of the value of brash as a nu trient source for second rotation crops. Most of the K (around 100 kg ha(-1)) and one-third of the P (10 out of 30 kg ha(-1)) leached out of the brash lying on the CH plots within one year of felling. A pulse o f K passed through the soil profile, but less than half this K reached the streams. In contrast, the P was immobilized in the soil. The lack of brash resulted in the absence of K and P pulses on the WTH plots. On the CH plots, brash was a net sink for inorganic-N for 3 years afte r felling. However, in both CH and WTH, a pulse of nitrate was observe d in the soil and also in streams draining CH areas. The source of thi s nitrate may have been death of fine tree roots, followed by rapid mi neralization and nitrification. Calculation of a nutrient budget for a complete crop rotation indicates that P and Ca losses in harvested ma terial are likely to result in long-term depletion of these elements, and that the effects will be significantly more severe if WTH is pract ised.