Organic fertilization has been shown to benefit soil biota. A field experiment was established in 1991 at the AGES experimental research station Ritzlhof to investigate the effects of long-term fertilization on soil biota and crop yields. Experimental plots were cultivated using a crop rotation with maize, wheat, barley, and pea. Eight treatments consisted of compost application (urban organic waste, green waste, cattle manure, and sewage sludge compost). Composts were applied exclusively (organic) or amended with mineral nitrogen (N) fertilizers (80 kg N ha−1, organic-mineral) and compared to 0 (control) and mineral (40, 80, and 120 kg N ha−1) fertilization. Earthworm activity and biomass, litter decomposition, crop growth, and yield parameters were investigated under winter barley (