Short-rotation plantations of balsam poplars, aspen and willows on former arable land in the Federal Republic of Germany. III. Soil ecological effects

摘要

As part of an interdisciplinary research programme, soil ecological effects of short-rotation forestry were studied in 3 experimental plantations on former arable soils in southern (Abbachhof, ABB), central (Canstein, CAN) and northern (Wildeshausen, WIL) Germany between 1983 and 1996. The methodological approach included a partly factorial fertilizer trial with N, P, K, Mg and Ca. Representative treatments and plots of those trials were used in comparative top soil inventories (0-30 cm) at the very beginning of the experiments and 10 (ABB and CAN) and 7 (WIL) yr after planting with poplar clones (balsam poplar, Populus trichocarpa cv. 'Muhle Larsen'; and aspen, P. tremula X tremuloides cv. 'Astria') and willows (Salix viminalis) in order to investigate the effects of afforestation on soil pH, exchangeable cations, organic carbon and total nitrogen. In addition, at the WIL site, the temporal variation of mineral nitrogen contents in the soil (0-100 cm) was investigated during 1989-1996. Soil pH (H2O) decreased significantly in the whole top soil at sites ABB and WIL, and in the top 10 cm at CAN by ca. 0.5 units. This slight acidification also showed in lower pH (CaCl2) values at ABB and WIL, but not at CAN. Total CEC (cation exchange capacity) decreased significantly at CAN by ca. 15% and diminished only slightly at ABB and WIL. Depth effects were not very pronounced. Ca saturation decreased, but Mg saturation significantly increased with time at ABB and CAN; minor changes occurred at WIL. At the start of the experiments, organic carbon was homogeneously distributed within the top soil horizons, but following afforestation, higher soil organic carbon was detected in the upper part of the profile, and with the exception of WIL, lower concentrations at 20-30 cm depth. A similar tendency occurred with total soil nitrogen. While at CAN and WIL, no significant change of total amounts of soil organic carbon and nitrogen occurred, contents of organic carbon increased and those of total nitrogen decreased with time at ABB. At WIL, afforestation lowered mineral soil nitrogen amounts compared with the agricultural control plots. In contrast, intensive soil cultivation and plantation establishment on grassland accelerated organic matter mineralizationcausing high losses of soil carbon (-15%) and nitrogen (-12%). Site specific management strategies are recommended for an ecologically sound afforestation of former agricultural soils, with high priority directed to avoiding nitrate leaching and contamination of the groundwater. The first 2 papers in this series (same special issue and authors, pages 41-55, 67-83) address site-growth relationships and nutritional aspects of the study.