|Austrian Bio-Indicator Grid – Supply of Nutrients|
PrefaceNitrogen, phosphorus, potassium, calcium and magnesium are all among the macronutrients of plants. Besides these macronutrients the micronutrients iron, manganese and zinc are determined with the aid of the Austrian Bio-Indicator Grid. All these elements as well as their ratios to each other are essential for healthy plant growth. There are various possible reasons for a deficiency or excess of nutrients, such as:
- inadequate soil nutrient supply
- continuous removal of nutrients (use of plant litter)
- leaching of nutrients (“acid rain”)
- one-sided nutrient enrichment (nitrogen input, magnesite dust…)
- impaired nutrient uptake (high soil pH, soil compaction…)
As with sulphur, each of the other nutrients is subject to fluctuations during the vegetation period. An assessment of the nutritional situation is therefore only possible at the end of the vegetation period (sample collection: October/November for conifers, September for deciduous trees). The values for the assessment of nutrient contents in the tree species spruce and pine are available here
One-sided nutrient enrichment can lead to nutrient excesses and inharmonious nutrient ratios, which both have a detrimental effect on the growth of trees. For that reason, effect-related threshold values for spruce needles are specified in the Austrian forest law “Zweite Verordnung gegen Forstschädliche Luftverunreinigungen, BGBl. Nr. 199/1984” as ammonia (2,2% N) and dust (0,3% P, 0,85% K, 0,9% Ca and 0,2% Mg).
Results of the Austrian Bio-Indicator GridNitrogen
The Bio-Indicator Grid shows that nitrogen is the most deficient nutrient in the Austrian forests. Up to 1992 the portion of plots with nitrogen deficiency went up as high as around 70%. Afterwards, the nitrogen supply situation improved. Only in 1994 and 2000 a high prevalence of plots with nitrogen deficiency was found again (nitrogen supply 1983-2003). There were great regional differences in nitrogen supply. The areas most deficient in nitrogen are in south Carinthia, the most well supplied areas are in the Mühl- and Waldviertel and in the Alpine Foothills (nitrogen supply in Austria).
Over the investigated years, the portion of plots with phosphorus deficiency averaged around 10%, so phosphorus is the second most deficient element in Austria after nitrogen. The highest portion of plots with phosphorus deficiency (25% of the plots) was detected in 2000. Phosphorus deficiency predominantly occurs in the Limestone Alps.
Magnesium deficiency could only be detected on around 1% of the investigated areas, so compared to other countries magnesium deficiency plays a minor role as a cause of damage to forests. Areas with deficiency of magnesium are most prevalent in Upper Austria (Alpine Foothills, Mühlviertel) and in Vorarlberg.
The investigated samples were mostly well supplied with the macronutrients potassium and calcium. Problems with the supply of micronutrients occurred only regionally. For instance at a few plots in the Mühlviertel and in the Upper Austrian Alpine Foothills, zinc deficiency was detected. Deficiency of manganese sporadically occurred in the Weinviertel and in south-eastern Lower Austria. A detailed description of the individual nutrient supply situations in Austria is provided in the Web-Database BIN-Online.