Nutrient uptake and immobilization in a short-rotation coppice stand of hybrid poplars in north-west France

Biomass and nutrient uptake were estimated, at harvest, in a short-rotation coppice plot of hybrid poplars (Populus trichocarpa x deltoides) monitored from planting. Soil reserves and restitutions by litterfall were also studied. For the two clones studied (cv 'Beaupre' and 'Raspalje'), total above-ground biomass reaches 88.8 and 74.7 t ha(-1) dry matter, respectively. Annual nutrient uptakes reached 92, 15 and 87 kg ha(-1), respectively, for N, P and K, for the most productive clone (cv 'Beaupre'). About 60-80% of this uptake returns to the soil each year through litterfall. Litterfall reaches 4-5 t ha(-1) year(-1) at age 7 or 8. Nutrient removal is estimated in relationship to the type of harvesting (logs or total biomass). Results for the coppices under study were very high compared to those of standard coppices. Restitution by fertilization was evaluated. Whole tree harvesting increases harvested biomass by 30%, but also increases N removal by 84%. Harvest of 7 cm small end diameter logs provides the best compromise between yield and nutrient exports. (C) 2000 Elsevier Science B.V. All rights reserved.