Pot experiments on the zinc nutrition of spruce seedlings in relation to the new kind of forest decline

In a pot trial with spruce seedlings growing in washed quartz sand, Zn concentration in needles could be reduced to 13 ppm in dry matter, but no visual symptoms of Zn deficiency appeared within two years. With Zn applied at 0.31 mg/kg substrate concentrations in seedlings were up to 133 ppm with no symptoms of damage or inhibition of growth. Needle contents of Zn, Ca, Mg, Fe and Al increased from year 1 to year 2. Zn content decreased in case of Ca- or Mg- and especially in combined Ca and Mg deficiency; when no Zn was applied in the second year, the lowest values were recorded. Zn content was positively correlated with N, K, Ca, Mn, and Fe, and N with Mg and Mn. There were no other antagonistic effects of Zn. The best growth of 2 year old seedlings was at needle Zn contents of 28–36 ppm in one year old and of 93–112 ppm in two year old needles. Spruce on areas of new forest damage has a lowered Mg content and lessened accumulation of Ca and Mn with increasing needle age as well as low Zn content (despite atmospheric deposition of Zn). Such low Zn levels could only be achieved in pot culture by taking strong precautions against contamination. Ca + Mg + Zn fertilizer should be tested on strongly acid upland soils low in Zn.