Using Organic Residues for Fertilization in Maize–Ryegrass Rotations to Enhance Circular Agriculture

Abstract

The increasing demand for sustainable agricultural practices has driven growing interest in organic fertilizers derived from waste streams as alternatives to mineral fertilizers. This study evaluated, in a pilot trial, the effectiveness of using raw digestate, composted digestate and composted sewage sludge in a crop rotation over two consecutive years of maize and Italian ryegrass. Crop yield, forage quality, and soil physicochemical properties were assessed to determine the potential of these recycled organic nitrogen sources. The results differed between the two species of forage. In maize, organic fertilizers maintained yield and forage quality comparable to chemical fertilization, while composted sewage sludge significantly increased average plant height. These findings indicate that recycled organic amendments can partially or totally replace mineral nitrogen fertilizers, contributing to nutrient recycling and waste valorization within a circular economy framework. In contrast, Italian ryegrass showed lower yield under organic fertilization than under chemical fertilization, suggesting that additional management strategies may be required to optimize nutrient availability for this crop. Furthermore, raw digestate application tended to increase soil pH, which may provide benefit subsequent crop. Overall, the results suggest that digestate and sludge-based fertilizers are promising alternatives for maize performance, although their effectiveness in Italian ryegrass requires additional strategies.