Abstract
Grass-clover leys allow sustainable intensive forage and livestock production but large pedoclimatic differences make mixture × cultivar trials necessary to identify site-specific optimal combinations. We addressed experimentally the questions: (1) whether cultivars of Trifolium pratense must be evaluated in a specific seed mixture, or whether their biomass and N yield and symbiotic N2 fixation can be ranked in any mixture; and (2) whether mixtures perform differently depending on the choice of T. pratense cultivar. The trial was set up with three cultivars (Milvus, Semperina, Spurt) and three regionally recommended grass-clover mixtures (IR, KG, WW), differing, among others, in T. pratense abundance. At the third cut after autumn seeding, T. pratense dominated the dry matter and N yield in mixture- and cultivar-specific manners. Irrespective of mixture and T. pratense cultivar, 56.7±1.1% of total N was acquired via symbiotic N2 fixation, owing to compensatory dynamics in sward structure and degree of reliance on N2 fixation. Cultivars Spurt and Milvus boosted dry matter and N yield, with cv. Spurt accumulating most N, and cv. Semperina tending to acquire proportionally most N via symbiosis. Our findings suggest that mixture × cultivar evaluation trials may not always be necessary as long as the mixtures are of similar composition and demonstrate N yield stability, despite different structure.