Correction of magnesium deficiency in a young stand of Norway spruce

A trial testing of the effect of several types of Mg fertilizer was established in a 9 yr old plantation of Norway spruce at the Col du Donon in the Vosgian mountains (France). The plantation, which had exhibited symptoms of Mg deficiency (yellowing), had been fertilized 5 yr prior to this study with 40 kg ha^–1 of Mg applied as Epsom-salts. This alleviated the deficiency symptoms, but the yellowing reappeared 3 yr after the fertilization and increased until the year in which the second fertilization trial (described in this paper) was established. Five Mg fertilizers (2 forms of slag, 2 forms of limestone, and Epsom-salts) at two rates of Mg (40 and 80 kg ha^–1) were compared to a control. Just after this second fertilization, the trees became green again and small positive effects on circumference and basal area increments has been observed. However, 12 yr after the treatment, there were no differences between the treatments regarding needle coloration, circumference, basal area or volume.