Continuous cultivation in solar greenhouses degrades black soil, leading to soil-borne diseases, nutrient imbalances, reduced porosity, and microbial dysbiosis, all of which collectively decrease crop productivity. Improving soil structure and microbial balance often requires costly amendments that are inconsistent in their effectiveness. This study evaluated two low-cost soil amendments—carbonized rice hull (CRH) and fermented rice hull (FRH)—using colored pepper as a model crop. Treatments included soil mixed with 30% CRH (T1), 30% FRH (T2), and untreated black soil (CK). Both amendments significantly improved soil physical properties. Compared with CK, soil porosity increased by 8.80% in T1 and 17.84% in T2, while water-holding capacity increased by 75.32% and 133.45%, respectively. Soil microbial richness, as indicated by Abundance-based Coverage Estimator (ACE) and Chao indices, followed the order T2 > T1 > CK. Plant physiological performance was also enhanced. Net photosynthetic rate increased by 7.18% (T1) and 15.33% (T2), plant height increased by 14.42% (T1) and 28.85% (T2), and root activity improved significantly. Fruit weight increased by 15.33% in T1 and 21.62% in T2. Both rice hull amendments improved soil quality and promoted crop growth, with FRH performing consistently better. These findings indicate that fermented rice hull is a promising, low-cost strategy for greenhouse soil remediation.