Soil degradation, water scarcity, and plastic residue accumulation pose significant challenges to sainfoin (Onobrychis viciifolia L.) production under ridge-furrow rainwater harvesting (RFRH) in semiarid region. This study was aimed to optimize ridge width and straw length under novel RFRH integrated with straw-soil crust improving carbon sequestration and sainfoin production. A Three-year field experiment was carried out using a randomized block design comprising 10 treatments and 3 replications. Treatments were 3 ridge widths (30, 45, and 60 cm) x 3 mulching materials (ridges integrated with soil crust (SC), short-chopped straw-soil crust (SSC, 2 cm), and long-chopped straw-soil crust (LSC, 10 cm)), and conventional flat planting (FP) as a control. The RFRH integrated with chopped straw-soil crust increased runoff, soil water storage (SWS), soil organic carbon (SOC), fodder yield, and water use efficiency (WUE) of sainfoin. Runoff coefficient for the ridge widths of 30, 45, and 60 cm was 0.23, 025, and 0.28, respectively, while for SC, SSC, and LSC was 0.21, 0.25, and 0.30, over three years. Compared to FP, the increase in SWS for the ridge widths of 30, 45, and 60 cm was 15.2, 23.5, and 32.6 mm, respectively, while for SC, SSC, and LSC was 14.4, 22.6, and 34.3 mm. The increase in SOC for the ridge widths was 20.1%, 33.5%, and 44.7%, respectively, while for straw lengths was 24%, 31.5%, and 42.8%. The increase in fodder yield for the ridge widths was 8.5%, 16.8%, and 28.9%, respectively, while for straw lengths was 13.4%, 17.4%, and 23.5%. The increase in WUE of sainfoin for the ridge widths was 2.0, 3.2, and 5.4 kg ha-1 mm-1 , respectively, while for straw lengths was 2.3, 3.2, and 5 kg ha-1 mm-1 . Structural equation modeling revealed that ridge width showed direct positive (standardized path coefficients = 0.56***) effect on SOC and indirect positive (standardized path coefficients = 0.15*) effect on WUE of sainfoin, while straw length demonstrated direct positive effect on SOC (standardized path coefficients = 0.41***) and WUE of sainfoin (standardized path coefficients = 0.15*). The Runoff coefficient, SWS, SOC, fodder yield, and WUE of sainfoin increased as the ridge width and straw length increased. In RFRH, wide ridges (60 cm) integrated with long-chopped straw-soil crust (10 cm) enhanced carbon sequestration and sainfoin production, offering viable replacement to plastic film mulching in semiarid region.