<p>Soil quality evaluation (SQE) is a vital aspect of environmental assessment and monitoring. Traditional SQE methods often use composite indices that can mask changes in individual soil properties, limiting detailed understanding of soil degradation. Effective management, however, requires parameter-specific insights. This study employs a novel Parametric Soil Quality Index (PSQI) to assess the impact of various cropping systems on individual soil properties, quantify percentage changes, and inform targeted soil quality improvements in smallholder farming systems. The PSQI captures specific variations across six land-use types—including sesame, guinea corn, yam, maize + yam mixed cropping, maize monocropping, and a natural forest control—providing a more precise tool for evaluating soil degradation and guiding site-specific interventions. Five hundred seventy-six composite soil samples were collected from these plots in Abuja, Nigeria. Chemical properties were analyzed using <i>t</i>-tests, one-way ANOVA, percentage equivalence, and percentage change to compare effects by soil depth and cropping system relative to the control. Results show significant soil quality degradation under cropping systems compared to natural forest, with soil organic carbon and total nitrogen declining by over 50% in some systems, especially sesame and guinea corn. Mixed cropping (yam + maize) better maintains nutrients such as potassium and cation exchange capacity. Changes in available phosphorus, exchangeable cations, and base saturation further reflect degradation due to intensive cropping and residue removal. The PSQI effectively quantifies these trends, highlighting both declines and improvements. The study recommends integrated soil fertility management, organic amendments, mixed cropping, precision farming, and agroforestry practices to sustain soil productivity.</p>