Influence of a sand soil plough base on the growth of Douglas fir (Pseudotsuga menziesii (MIRB.) FRANCO).

The root/shoot growth of eight year old Douglas fir trees (Pseudotsuga menziesii (MIRB.) FRANCO) planted on ploughed agricultured land in the first generation was investigated. One half of the field was 60 cm deeply ploughed before afforestation. The second half was not deeply ploughed and was compacted at a depth of about 35 cm (Fig. 2) due to the influence of agricultural machines. To describe the plough-base the dry weight of soil, the hydraulic capacity and the distribution of the volume of the pores were measured (Fig. 3). The penetrometer resistance-measurement visualised the compactness quiet dearly (Fig. 2). Furthermore an analysis of texture and of the exchange capacity was done. The root systems in the deep-ploughed and not ploughed plots of the afforestation were compared. For description each root system was cut in vertical sections of ten centimetres (Fig. 1). At the cutting point the cross-section of the roots was measured, and for each section the dry weight of roots was recorded. It could be found out that the root as well as the shoot growth of the Douglas fir trees on the unploughed half of the afforestation was less vigorous than on the deeply ploughed half (Fig. 4 to 7). The trees on the unploughed and deeply ploughed stand had developed different root systems: flat root systems on one hand and heart root systems on the other. It is obviously, that the soil compactness (Fig. 2) primarily causes the depression in root development and secondarily to the whole slow tree growth. Furthermore the flat rooting trees on the unploughed stands are susceptible for droughts, the high mortality of trees seems to be the consequence.