Silicon Enhances Yield in Dry-Cultivated Rice/Soybean Intercropping Systems by Altering Root Morphology and Distribution

Intercropping cereals and legumes can increase agricultural productivity, but the effects of silicon (Si) fertilizer application on intercropped crop yield and interspecific root interactions in cereal/legume intercropping systems are unclear. Hence, field and pot experiments were conducted with dry-cultivated rice and soybean grown alone or intercropped under two Si levels (0 and 45 kg ha⁻¹) to investigate the effects of Si application on the yield, root morphology, and distribution of dry-cultivated rice/soybean intercropping systems. The results revealed that the total yields of the intercropping and monoculture systems were 15% and 13% greater, respectively, under Si application (Si45) than under no Si addition (Si0). Compared with the yield under monoculture, the total yield under intercropping increased by 5% and 7% under Si0 and Si45, respectively. This overyielding leads to a land equivalent ratio > 1 under both Si levels. This increase was primarily due to a 24% increase in intercropped soybean yield, despite a 7% decrease in rice yield averaging the two Si levels. The crop yield was positively correlated with root morphological traits, and the root surface area was the most significant predictor of crop yield. Intercropped soybean demonstrated a competitive advantage over rice. Thus, the root morphology traits of soybean were promoted, whereas these parameters in rice were inhibited by intercropping. Compared with Si0, Si application significantly promoted the root morphology and distribution traits of both crops in the intercropping system. Overall, the application of Si during dry-cultivated rice/soybean intercropping significantly enhanced yield production by modifying the root morphology and distribution.