Forage production in pasture-based agrivoltaic systems in desertified regions is often constrained by poor soil quality and the microclimatic effects of photovoltaic (PV) panels. In this study, coal gasification coarse slag (CGCS) were applied to overcome these limitations. We conducted coupled pot and field experiments within an agrivoltaic framework using Medicago sativa (alfalfa) and Elymus sibiricus. We specifically evaluated the interaction between CGCS amendment rates and PV shading patterns (high-light inter-panel zones vs. shaded subpanel areas), focusing on a 20% CGCS dosage at 50-70% field capacity (FC). In the agrivoltaic system, the 20% CGCS amendment maximized biomass for both species. Crucially, the PV structure created distinct niches: alfalfa exhibited superior growth and soil erosion resistance in high-light inter-panel zones, while E. sibiricus achieved greater leaf area and biomass under the panels. Field results confirmed that CGCS enhanced soil nutrients and microbial activity, with alfalfa showing strong nitrogen fixation under high light and E. sibiricus maintaining stability in shade. We propose an optimized agrivoltaic configuration: cultivating alfalfa between panels and E. sibiricus under panels, coupled with 20% CGCS and 50-70% FC. This strategy transforms industrial waste into a resource, offering a scalable, cost-effective solution for sustainable forage production and land restoration specifically tailored to agrivoltaic systems in arid ecosystems.