Crop Growth and Yield in Three-Crop Mixtures and Sole Stands in an Organic System

Low yields remain a primary obstacle to the expansion of organic farming in Europe. While legume-based mixed cropping enhances land-use efficiency, three-crop mixtures remain understudied compared to binary systems. We evaluated the vegetative and generative growth of pea (Lathyrus oleraceus Lam.), oats (Avena sativa L.), and camelina (Camelina sativa (L.) Crantz.) in sole stands versus three-crop mixtures in southern Finland. Experiments were conducted over two years using varying relative seeding densities (including 50:20:30, 50:50:50, and 33:33:33). Biomass dynamics and seed quality were analyzed using analysis of variance (ANOVA), while interspecific interactions were quantified using the relative interaction index (RII) and land equivalent ratio (LER). In 2022, mixtures increased oat seed protein by 11% relative to sole crops, achieving a biomass LER of 1.17. In 2023, oats exhibited strong competitive dominance (RII > 0.3), which concurrently reduced camelina quality. Notably, the 33:33:33 mixture consistently achieved a biomass LER > 1.2 and marked improvements in pea growth rates. Across all mixtures, the seed yield LER reached 1.04. These results suggest that three-crop mixtures can enhance productivity in Nordic organic agriculture with minimal quality trade-offs. Practically, we recommend the equal seeding density (33:33:33) as the optimal configuration for maximizing resource use efficiency, though further optimization of species combinations is encouraged.