Maize/alfalfa intercropping enhances yield and phosphorus acquisition

Context: The mechanisms underlying belowground processes in a perennial legume-dominated cereal/legume intercropping system were largely unknown. Objective: This study aimed to investigate whether alfalfa/maize intercropping can increase yield, phosphorus (P) uptake and utilization efficiency by influencing root morphology and distribution. Methods: Maize (Zea mays L.) and alfalfa (Medicago sativa L.) were grown in three different strip intercropping patterns and sole monocultures (monocultured maize, MM or monocultured alfalfa, MA), in field with or without P application from 2015 to 2018. Results: Intercropping increased total yield by 68% compared with MM, and by 19% compared with MA; P uptake and P use efficiency of intercropping increased by 61% and 53% compared with the averaged monocultures, respectively, when considering all intercropping patterns and four-year results. This resulted in an enhanced land equivalent ratio (LER) based on yield and P uptake ranging from 1.13 to 1.62, with a higher LER observed under no P application. The intercropping pattern of four rows of maize and six rows of alfalfa with a row spacing of 30 cm had the greatest yield, leading to the highest LER among all the intercropping patterns. The positive complementary effect of intercropped alfalfa plays a crucial role in the observed advantages of maize/alfalfa intercropping. Intercropping increased alfalfa yield and P uptake. P uptake of alfalfa was positively correlated with the lateral root surface area. However, maize was at a competitive disadvantage under intercropping, the yield and P uptake was decreased compared to MM. P application increased total yield and P uptake averaged by 33% and 57%, respectively, compared to no P application. Phosphorus uptake efficiency was significantly higher under intercropping patterns (19.2%) compared to monocultures (9.0%) with P application. Conclusions: The complementary effect of intercropped alfalfa promoted the overall system yield and P uptake. The facilitative effects of maize/alfalfa intercropping were more pronounced in low P soils than with P application. The intercropping pattern of four rows of maize and six rows of alfalfa with a row spacing of 30 cm was recommended as the most productive cropping pattern. Implications: Maize/alfalfa intercropping are promising approaches to establishing productive and sustainable managed ecosystems, when designing a perennial legume-dominated cereal/legume intercropping system.