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Abstract "Heft 21"


Freiburger Bodenkundliche Abhandlungen

Schriftenreihe des

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


Heft 21


Jin Chen Liu

Ernährungskundliche Auswertungen von diagnostischen Düngungsversuchen
von Fichtenbeständen (Picea abies Karst.) Südwestdeutschlands


Freiburg im Breisgau 1988

ISSN 0344-2691


Summary:

Nutritional Evaluation of Diagnostic Fertilization of Norway  Spruce  (Picea abies Karat.) in Southwest Germany
Evaluating diagnostic fertilization of Norway spruce (Picea abies Karst.) in Southwest Germany, the effect of easily soluble salts on soil chemical characteristics, and the nutrient supply of the stands and damage symptoms were investigated. Further more it was attempted to explain some of the primary causes of the "new type" forest damage.
The 27 sites investigated, differed in parent material and soil type. The stands were between 8 and 113 years old with the majority aged between 50 and 100. 57 trial plots were fertilized with N, K, Mg, Ca, Mn and Zn in varying combinations and rates. All the fertilizers were easily soluble nitrate and sulphate salts.
The soil parameters (Nt, Corg , 1 % citric acid soluble P, exchangeable K, Mg, Ca, Mn, Fe, Al, H, pH, and particle size distribution) and the element contents in the needles (N, P, K, Mg, Ca, Mn, Fe, Al, Zn) were determined before fertilization in 1983/84. Two years after fertilization in 1986, the measurements above were repeated, with additional damage symptoms (needle yellowing, needle reddening and needle loss in particular) being surveyed, and S concentrations in the needles were measured.
The measured soil parameters of the crystalline sites had a spatial variability below 30 %. On the calcareous loam sites it was higher. pH values, exchangeable K, Mg and Al had the lowest variation. Those elements with lower concentrations in the soil generally had the highest variation ( above all Fe and often P) . Normally the variation of the element contents in needles was lower than that of the soil. Mn, Ca and Mg contents had the highest variation (30, 29 and 24 % respectively), and N and K the lowest. The contents in older needles (IV.4) showed a greater variation than in young needles (I.I). The damage symptoms (needle yellowing, needle reddening and needle loss) varied spatially very strongly. In most cases it was above 100 %. Hence, a representative survey of damage symptoms would have required more than 100 samples per plot. However, the stand characteristics (100 needle weight, the maximum age class of the needles, mean height of the stands and height growth) were spatially very homogeneous.
The nutrient supply of the soil was dependent on the parent material. According to the soil critical levels for Norway spruce, K supply of moraine, Ries destrital material and loess was considered critical. The Mg supply of porphyr, granite, gneiss and loess was found very low.
The saturation degree of absorbed cations on exchange complexes was largely effected by pH levels. At pH (H2O) above 5, ca was dominant. K, Mg and Mn, exhibited a maximum of their saturation at pH (H20) of about 5. pH values below 5 were accompanied by an increase of Al, H, and Fe saturation. At pH below 4 these three cations amounted to 80 % of the exchange capacity.
The soil parameters varied considerably during the years. From 1984 to 1986 the concentrations of exchangeable K, Mg, Ca, Mn, Fe and H in the topsoil (0-10 cm deep) increased significantly. The pH values were, however, unchanged. The increase of exchangeable K, Mg, Ca, Mn, Fe, and H was probably due to higher mineralization of organic substances caused by relatively high humidity in 1986.
The fertilization effects of K, Mg, and Ca were observed over the entire study period and were dependent on the rates of fertilizer applied. Two years after the fertilization most of the applied Ca and Mg was still present in the topsoil (0-10 cm). This confirmed that these two elements move relatively slowly in the soil. However, K showed a higher leaching in the deeper soil. The results from the fertilization allowed a calculation of the fertilizer requirements under different initial situations to be made.
A pH decrease caused by a push of acidity was observed only on the plots with of sulphate fertilizer. The highest pH decrease was 0.9. The mean value of pH decrease was determined between 0.2 and 0.3. With initially higher pH levels, the pH decreased more than at lower levels. The nitrate fertilization generally influenced pH values positively. The higher the N03 uptake, the higher the pH increase.
Except for N and P, the element contents in needles varied considerably from 1983 to 1986. Variations above 50 % were often observed. A significant increase of Mg and Mn contents was shown. The contents of other elements did not show a statistical change. The variations of Mg and K contents in needles were due to the variation of the exchangeable fraction of the same elements in soils.
Considerable effects of K, Mg, Ca, and Zn fertilization were observed on those elements that suffered from the corresponding deficiency. Nitrate fertilization did not improve the N contents in needles. S contents in needles were not altered on the plots fertilized with sulphate. Fertilizer applications without nitrate caused a decrease of N and P contents in needles. On some plots P deficiency was induced through nitrate application which decreased P contents in needles.
Needle yellowing and needle loss was reduced by fertilization. The effects were particularly visible when the symptoms had been very strong. The decrease of needle yellowing was correlated with the increase of Mg contents in needles. However, this effect was not observed for needle loss. Needle reddening responded very differently after fertilization because it was also influenced by biotic factors.
A significant relation was observed between damage symptoms and the nutrient contents in needles. The Mg contents played a decisive role. The contents of Mg, Ca, and Mn correlated with needle yellowing negatively but positively with P, S, K, and Fe. The situation of the needle reddening was reversed. This showed, that needle reddening must be considered as an independent symptom and not belonging to the "new type" forest damage.
A so-called nitrogen ratio (a dimension of proportion of NH4-N on total N in the root uptake) was introduced, to describe the nutritional status causing needle yellowing.
By multiple analysis the relation were investigated between element contents in needles and the degree of needle yellowing on the one hand and the nitrogen ratio as well as nutrient supply of soil on the other hand. The results demonstrated, that the nitrogen ratio had a decisive influence on the uptake of other elements. A higher nitrogen ratio supported anion (P, S) uptake and impaired cation (Mg, Ca, Mn) uptake. However, the nitrogen ratio did not effect the K uptake, because K is actively taken up by plants.
To Summarise: the needle yellowing and needle loss of the investigated forest sites were clearly symptoms of Mg deficiency. This is caused by lack of Mg in soil varying strongly in relation to climatic conditions, and high ratio of NH4-N uptake. The high NH4-N uptake was probably due to Mo-deficiency.



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