[Microbiological and chemical investigations into amelioration of spruce raw humus on phosphorus-deficient sites in the Mittelgebirge (author's transl)].

In spruce stands on quartz-porphyry sites raw humus is formed on strongly acid, calcium and phosphorus-deficient soils which were treated with lime, phosphate, and ammonium nitrate individually and in combined form. The most favourable microbiological and chemical effect was attained by CaNP fertilization, which is suitable for raising the yield of spruce stands with simultaneous amelioration of raw humus. The long-term effect of the phosphate is bound to simultaneous liming which ensures the persistence of phosphorus in the A0 horizon. The nitrification-based nitrate content of the soil is increased in the variants CaNP, CaNP and, to a somewhat lesser extent, also in NP. Simple treatment with N hardly raises the bacteria content, the combinations CaN, NP, and particularly CaNP, on the other hand, gave a favourable effect. Germination number and number of species of actinomycetes are also furthered most effectively by CaNP. The percentage of fungi in the total number of germs is reduced by fertilization without negatively influencing the species spectrum. Liming has a negative effect on the absolute germination number of the fungi, treatment with N gives a positive effect. The metabolism conditioned by microbes in the raw humus is not activated by N, moderately by NP, and strongly by CaNP.