Abstract BACKGROUND Narrow‐leaved lupins (NLL, Lupinus angustifolius L.) is recognized as a climate‐resilient protein crop but its use in food and feed is frequently limited by toxic quinolizidine alkaloids (QAs). The effect of intercropping with spring oat ( Avena sativa L.) on grain QA content has not yet been quantified. RESULTS In a 2‐year field experiment, three NLL varieties ( Lunabor , Probor , and Jowisz ), grown as pure stands and in nine mixtures with the oat varieties Bison , Lion , and Troll were compared. Mixed cropping increased total grain QAs by between 16% and 46% relative to the respective pure stands. Absolute increases reached +168 mg kg −1 in Lunabor and +128 mg kg −1 in Probor , whereas Jowisz increased by only +76 mg kg −1 . Among the mixtures, Jowisz – Bison exhibited the smallest increase (16%) and the lowest final QA content, whereas Lunabor – Troll showed the highest content. In mixed stands, both Lunabor and Probor exceeded the 500 mg kg −1 threshold, whereas Jowisz remained below this threshold. Profiles of the seven major QAs remained constant, with the exception of the 13‐hydroxylupanine to lupanine ratio, which increased in the mixture. Year effects were not observed. Conclusion Intercropping NLL with oat elevates the grain QA content to levels of toxicological relevance. The extent is variety‐interaction dependent, presumably due to oat allelopathy. The evidence points to an indirect stress mechanism: allelopathic cues from the oat crop place NLLs under physiological stress, which in turn stimulates NLL to accumulate additional QAs in the grain. Additional mixed cropping experiments and breeding against QA accumulation in NLL grains should be pursued to understand and alleviate this issue. © 2026 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
Schlup et al. (Wed,) studied this question.