Chemical-physical and biological indicators of soil health in agricultural systems after a 20-year field study in Northern Italy

Abstract Soil biodiversity responds to agricultural management, yet its relationships with soil condition and crop productivity remain insufficiently resolved. We assessed soil health indicators at the end of a 20 years experiment involving six cropping systems in northern Italy, i.e. continuous maize, annual and multi-year rotations, permanent grassland, and rotational meadow—under standard and reduced-input management. Soil physicochemical properties, aggregate stability, microbial respiration, crop productivity, and nematode abundance, diversity, maturity, trophic composition, and food-web indices were evaluated using a multi-indicator approach. Cropping-system identity differentiated soil conditions more clearly than input level. Permanent grassland had the highest organic matter content (3.3–3.9%), mean air-dried soil structure stability (67.7%), and nematode richness (up to 29 taxa), together with high food-web structure. Continuous maize supported the greatest nematode abundance (approximately 700 individuals per 100 g dry soil under standard management), but showed low Maturity Index values (1.49 and 1.16 under standard and reduced inputs), low richness (12 and 10 taxa), and dominance by opportunistic bacterivores. Rotations occupied intermediate positions: annual succession and three-year rotation had Maturity Index values around 2.3, while annual succession and the six-year rotation achieved the highest productivity. Standard management produced a higher mean yield than reduced-input management (11,457 vs. 9,812 UFL ha⁻¹), although the latter showed smaller interannual fluctuations. Nematode community composition and functional indices distinguished systems more clearly than total abundance alone and complemented physicochemical, structural, and microbial indicators. Contrasting rankings for biodiversity, soil structure, and productivity revealed trade-offs obscured by single indicators. Integrating nematode-based metrics into long-term, multi-indicator assessments may support strategies reconciling agricultural production with soil biodiversity conservation.