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Abstract "Heft 7"


Freiburger Bodenkundliche Abhandlungen

Schriftenreihe des
Institut für Bodenkunde und Waldernährungslehre
der Albert-Ludwigs-Universität Freiburg i.Br.
Schriftleitung: F. Hädrich


Heft 7


Günther Schäfer


Nährelementhaushalt von Kiefernjungbeständen in der
südlichen Oberrheinebene


Freiburg im Breisgau 1977

ISSN 0344-2691

Summary:

In the pine reforestations of the Rhine River valley near Breisach the following were investigated:
a)    the nutrient distribution in the forest stands, ground vegetation, and soil
b)    the nutrient supply to the forest stands.

1.    After the lowering of the groundwater level, the soil can be classified today as a man influenced fluvisol (Kalkpaternia-Pararendzina) with a two layer profile: sandy-silty topsoil to a depth of 20 - 30 cm overlying sandy gravel.
2.    The biomass (dry matter) and the nutrient contents of the compartments of a 15 year old Pinus nigra (Arn.) and a 16 year old Pinus silvestris (L.) stand were comparatively analyzed and their annual nutrient uptakes calculated. With a comparable stocking per unit area and a definite inferiority in height growth, the Austrian pine produces  12 % more biomass; and for this requires a lower nutrient supply than Scots pine, while it absorbs more potassium (+ 27%) and excludes more calcium (- 4%). The Austrian pine is thus superior in its utilization of the site.
3.    The biomass of the ground vegetation in the pine stands and its nutrient content as well as the changes therein with progressive stand development were determined. With stand closure a reduction in dry matter and a great change in the species composition of the ground vegetation occurs. This process causes a release of nutrients in the range of a fertilizer application (in two growing seasons, per ha: ca. 100 kg N, 1.0 kg P, and 100 kg K). The availability of these elements clearly stimulates tree growth.
4.    The soil has high nutrient reserves. However, due to the dry site conditions and the low rate of chemical weathering, the nutrient availability is in part much reduced. This is especially true for potassium of which only 0.2% of total content are "available".
5.    Investigations on the output of nitrate and potassium showed that percolation losses were minimal and occured only during the time from January to March. Water sprinkling experiments demonstrated that even under unfavorable conditions the output of nitrate is insignificant, while K-losses can attain a certain significance during winters with above average precipitation (K-losses may amount to 10 - 20 % of the annual stand uptake).
6.    The dynamics of the nitrogen supply to the stands were clarified using laboratory incubation procedures as well as by the determination of the actual nitrate concentration in the field. The results demonstrated the importance of the regular alterations from dry to wet phases. Partial sterilization with a correspondingly high production of microbially useable compounds and a high turnover of new mineralizing populations led to a great increase in nitrogen mineralization upon re-wetting after a dry period. The incubation trials showed that mineral nitrogen is supplied even under very dry conditions.
7.    The nutrient status of different aged Scots pine and Austrian pine stands were investigated from needle analyses. In 10 year old sapling stands the N, P, K, and Mn contents are deficient. With increasing stand age, the nutrient supply of these elements clearly improves. The status of potassium and manganese in Pinus silvestris stands, however, remains deficient. Pinus nigra evidences a distinctly more favorable K:Ca ratio.
8.    The fertilization trials conducted from 1961-1966 showed a small but significant positive effect for P. silvestris. The greater height growth of the NPK plots compared to the controls amounted to a 13% increase until 1975.
The Austrian pine stands exhibited no significant differences in total height growth, though great variation in annual height growth appeared.
Part of the added fertilizer nutrients were taken up by the ground vegetation and thus only reached the pine rooting zone after ground vegetation death due to stand closure. This caused the highly significant increases in growth on the fertilized plots in 1974 and 1975.


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