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

Abstract As part of an interdisciplinary research program, soil ecological effects of short-rotation forestry were studied at three 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 fertilization trial with the nutrients 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 seven (WIL) years after afforestation with poplars and willows in order to investigate afforestation effects on soil reaction, exchangeable cations, organic carbon and total nitrogen in top soil (0–30 cm). In addition, at one site in northern Germany, the temporal variation of mineral nitrogen contents in the soil (0–100 cm) was investigated during 1989–1996. Soil reaction (in H 2 O) 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 shows up on a lower level in the pH (CaCl 2 ) values at ABB and WIL, but not at CAN. Total CEC eff 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 on the former arable soils, organic carbon was homogeneously distributed within the top soil horizons; following afforestation, higher C org values were detected in the upper part of the profile, and, with the exception of WIL, lower concentrations in 20–30 cm. A similar tendency showed up with total soil nitrogen. While at CAN and WIL, no significant change of total amounts of C org and N t occurred, contents of organic carbon increased and those of total nitrogen decreased with time at ABB. At WIL afforestation lowered mineral soil nitrogen amounts in soil as compared to agricultural control plots. In contrast, intensive soil cultivation and plantation establishment on grassland accelerated organic matter mineralization causing high losses of soil carbon (−15%) and nitrogen (−12%). Site specific management strategies are recommended for an ecologically sound afforestation of former agricultural soils, aiming to avoid nitrate leaching and contamination of groundwater with high priority.