Chemical-Physical and Biological Indicators of Soil Health in Agricultural Systems after a 20-Year field study in Northern Italy

This 20-year study in Lodi, Italy, evaluates the impact of various cropping systems on soil health, addressing the urgent need for reliable indicators to monitor sustainable agricultural transitions. Six systems—ranging from annual and multi-year rotations (R1, R3, R6) to permanent grass (PP), maize monoculture (MM), and permanent rotational meadow (Pa)—were analyzed under conventional and low-input management. Key assessments included soil structure stability (SSI), nematode community dynamics (diversity and Maturity Indices), and microbial activity (SOUR). The results highlight a clear contrast in soil resilience: permanent grass (PP) maintained the highest fertility and stability, with 3.3% organic matter and a 67.7% SSI. In contrast, maize monoculture (MM) led to significant degradation, characterized by low organic matter (1.0%) and poor structure (36.8% SSI). While MM exhibited high microbial respiration, this reflected rapid organic matter depletion rather than ecosystem health. Crop rotations provided moderate biodiversity and improved structure, significantly outperforming monocultures in ecological stability. Multivariate analyses confirmed strong correlations between soil biodiversity, structure, and fertility. Notably, nematode indicators proved more sensitive than traditional chemical properties in distinguishing the impacts of different management practices. The study concludes that monoculture is detrimental to soil health, whereas diversified rotations and permanent vegetation are essential strategies for long-term sustainability. These findings advocate for integrated management—combining crop diversification with reduced tillage—and reinforce the role of nematodes as effective bioindicators for assessing agroecosystem resilience.