Because crops differ in growth and resource-use strategy, it remains unclear whether mulching induces cross-crop consistency or crop-specific responses in soil properties, microbial communities, and community assembly processes. To address this gap, we conducted a four-year field experiment in the semi-arid rainfed region of northwestern China. Using no mulch (NM) as the control, we assessed the effects of straw strip mulching (SM) and plastic film mulching (PM) in maize (Zea mays L.), potato (Solanum tuberosum L.), and spring wheat (Triticum aestivum L.) fields. Compared with NM, SM increased soil organic carbon, microbial biomass carbon, total nitrogen, and ammonium nitrogen by 6.0-18.9%, 18.2-28.1%, 4.9-15.3%, and 11.8-84.5% (P < 0.05), respectively, across crops. It also showed cross-crop consistency in bacterial alpha-diversity, beta-diversity and community composition. In contrast, PM exhibited stronger crop-specific responses, particularly in nitrogen-related properties and bacterial community composition. Bacterial and fungal communities were assembled predominantly by stochastic processes, but mulching changed the relative contributions of drift and dispersal limitation. Both SM and PM increased drift and reduced dispersal limitation in fungal communities. In bacterial communities, SM reduced drift and enhanced dispersal limitation, whereas PM exhibited crop-specific responses. Co-occurrence network analysis indicated that SM increased network complexity and stability while raising the proportion of positive fungal-fungal and bacterial-fungal associations. In contrast, PM maintained network properties comparable to those of NM but increased positive bacterial-bacterial associations. Analyses showed that PM performed better in maize fields, with yield and net return increasing by 88.0% and CNY 3246 ha(-)& sup1; , respectively, whereas SM performed better in potato fields, with corresponding increases of 28.3% and CNY 4650 ha(-)& sup1; . Random forest and redundancy analyses identified ammonium nitrogen as the primary driver of alpha-diversity, whereas soil water content and total nitrogen were the primary drivers of community structure. In summary, straw strip mulching showed greater cross-crop consistency, whereas plastic film mulching was dominated by crop-specific responses. This indicates that mulching strategies in semi-arid rainfed areas should be optimized according to crop type.