Fall-planted cover crops improve nitrogen use efficiency but reduce garlic yield in a relay intercropping system amended with arbuscular mycorrhizal fungi.

Background: Integrating fall-planted cover crops (CC) and arbuscular mycorrhizal (AM) fungi into hardneck garlic production can enhance the sustainability of garlic production in the northeast. We hypothesized that relay intercropping (RI) garlic into standing CC and inoculating with commercially available AM fungi would (i) influence garlic bulb yield and nutrient concentration as a result of increased nutrient retention in CC residues and (ii) enhance the nitrogen use efficiency (NUE) of garlic production by providing an alternative N source (decomposing CC residues) to garlic plants in spring.

Results: Garlic yield response to RI depended on CC fall biomass accumulation (2301-3696 kg ha^-1 dry weight in 2021, < 1500 kg ha^-1 in 2020). Interspecies competition between CC and garlic reduced bulb yield by 21-31% in RI treatments compared to the no cover crop control in 2021. Although bulb N, P, K and Mn assimilation was negatively impacted in the first year, nutrient concentrations were normalized in the second cropping season, suggesting that multiple years are necessary to improve garlic quality under a RI system. Garlic yield and nutritional quality were not significantly improved by AM fungi inoculation in this study. NUE was optimized under oat RI systems, which had the highest yields among RI treatments in the second year.

Conclusion: RI with CC can improve NUE of garlic production systems, but CC should be managed appropriately to avoid reductions in bulb yield. Multi-year implementation of RI balances nutrient assimilation by garlic, which was negatively impacted in the first year of production. © 2025 Society of Chemical Industry.