Effects of two decades of organic and mineral fertilization of arable crops on earthworms and standardized litter decomposition

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 (Hordeum vulgare L.) in 2014 after uniform mineral fertilization and 1.5 years after the last compost application. Earthworm activity was significantly increased under long-term organic-mineral fertilization compared to the control, whereas earthworm biomass was unaffected by compost application. Litter decomposition rate was highest in the control. Only barley stem growth was affected by fertilization, whereas other barley parameters including yield were unaffected. The results showed that long-term fertilization affects soil biota even if compost is not applied every year.