© 2020 Elsevier B.V. Restoring physical quality of acidic Luvisols from the Ethiopian highlands subjected to long-term conventional tillage (CT) by traditional no tillage (NT) system may take 20–30 years. Use of exogenous additives may speed up reclamation of soil physical quality. The objective of the study was to examine the effects of combining two tillage systems (NT and CT) with additives (polyacrylamide [PAM] and lime) on accelerating structure stabilization of Luvisols. The high energy moisture characteristics (HEMC) method was used to evaluate: (i) the contribution of PAM dose (0, 25, 50, 100, 200 mg L−1) and slaked lime (1.6 g L−1), on pore size distribution (PSD), and structure stability indices of six soils, five under long-term cropland (CT-crop) and one under grassland for grazing (NT-grass), and (ii) the relations between the stability indices obtained from these six soils. Ethanol and deionized water were used for wetting of soil aggregates. The water retention curves of the samples were characterized by a modified version of the van Genuchten model that yields (i) the parameters α and n (that control the location and steepness of the water retention curve, respectively), and (ii) a soil structural stability index (SI). The results revealed that, compared with the control, the additives significantly altered soil PSD, increased SI and α, and decreased n (particularly with lime). Untreated NT-grass and CT-crop soil treated with low concentration of PAM (25 mg L−1) or lime, resulted in comparable SI, while high PAM concentrations (100−200 mg L−1) yielded 2–3 times greater SI values than untreated NT or CT samples. Exponential type relations were identified between SI and model parameters (α or n) or PAM dose. These relations could assist in evaluating the suitability of tillage system together with additives for stabilizing soil structure. Our result advocate the application of small doses of exogenous additives (PAM, lime), in combination with NT, for improving the structure and quality of acidic Luvisols at a faster rate.