The effects of mung bean and maize intercropping on maize root growth and nitrogen absorption in red soil under different compaction conditions

Cereal-legume intercropping can promote nutrient absorption by altering crop root morphology. However, its effects on root morphology and nitrogen absorption under compacted soil condition remain unclear. This study aimed to investigate the impact of maize/mung bean intercropping on maize root growth and nitrogen absorption under different soil compaction conditions. Non-compacted (1.2 g/cm³) and compacted (1.5 g/cm³) conditions were established, and three planting patterns were set under each level: maize monoculture, maize and maize intercropping, and maize and mung bean intercropping. X-ray computed tomography (CT) scanning technology and 15 N isotope labeling method were used to analyze maize root morphology, root-root interactions, and nitrogen absorption. The results showed that regardless of soil compaction, the above-ground biomass of maize in maize/mung bean intercropping was higher than that in maize monoculture and maize/maize intercropping. Maize/mung bean intercropping significantly increased maize root surface area, and also enhanced root volume and total root length compared to maize monoculture under no compaction. Compared with non-compacted condition, soil compaction significantly reduced the root surface area and total root length of maize in maize/mung bean intercropping by 52.32% and 55.92%, respectively, and also significantly decreased the root angle of maize under different treatments. The 15 N absorption of maize in both monoculture and maize/mung bean intercropping was significantly higher than that in maize/maize intercropping under no compaction, with increases of 120.34% and 122.03%, respectively. Under compacted condition, the 15 N absorption of maize in maize/mung bean was significantly higher than that in maize monoculture and maize/maize intercropping, increasing by 42.55% and 44.09%, respectively. Our results demonstrate that maize/mung bean intercropping promote maize root growth and improve maize nitrogen absorption even under soil compaction stress. Therefore, maize/mung bean intercropping can serve as a promising planting strategy for enhancing crop productivity in compacted soils.