Actavia 0 Scherer, H.W. Metker, D.J. Welp, G. 2011 2011-11-30 513-518 We studied the long-term effect (about 45 years) of farmyard manure, sewage sludge and compost application in two increments on organic carbon (C_org), the amount (C_mic) and activity of the microbial biomass (soil respiration, dehydrogenase activity), total N content and N delivery of soils as compared to manuring with mineral fertilizers. The application of both increments of compost and the high sewage sludge application rate resulted in an increase in C_org while soils treated with both compost application rates and the high farmyard manure application rate showed a significant increase in C_mic. C_mic/C_org ranged between 1.7 and 3.3. Dehydrogenase activity and soil respiration were the greatest in the soil with the highest compost and farmyard manure application rates. Total soil N content was significantly higher in both compost treatments and in the treatment with the high sewage sludge application rate. This was accompanied by the highest N uptake of ryegrass. 11 57