Yield advantage of the silage maize ‖ lablab intercropping system in response to spatial configuration

A well-designed soybean-corn intercropping system can provide significant yield advantages. However, the underlying mechanisms by which compensation and selection effects contribute to these advantages across ecologically distinct environments remain insufficiently understood. This study, conducted from 2021 to 2022, examined silage maize and lablab. Sole-cropped silage maize (SM) and sole-cropped lablab (SL) served as controls. Four intercropping treatments were established: silage maize interplanted with one (ML₁), two (ML₂), three (ML₃), or four (ML₄) lablab seeds per hole. To clarify the roles of the complementarity effect (CE) and selection effect (SE) in intercropping yield advantages, forage productivity, land equivalent ratio (LER), yield increase rate, relative interspecific competitiveness (RC), and net effect (NE) were analyzed across treatments. Results showed that intercropping silage maize with lablab significantly enhanced forage yield, with all intercropping systems outperforming monocultures. Among them, ML₂ yielded the highest total dry matter (35.19 t hm^-2) and crude protein (3.24 t hm^-2), representing increases of 28.48% and 64.64%, respectively, compared to SM. All intercropping treatments exhibited LER values greater than one. LER was significantly and positively correlated with the compensation effect, but negatively correlated with the selection effect. Similarly, yield increases in silage maize were positively associated with the compensation effect (<italic>P</italic> &lt; 0.001) and negatively associated with the selection effect. The productivity gains in ML₁ and ML₂ were primarily driven by the compensation effect, while those in ML₃ and ML₄ were mainly attributed to the selection effect. These findings suggest that as the proportion of lablab increases, the dominant mechanism driving yield advantages in the intercropping system gradually shifts from compensation to selection.