Daylength Influence on the Growth and Metabolism of Sainfoin

Abstract

Sainfoin's (Onobrychis viciifolia Scop.) poor growth following defoliation and lack of stand persistence have limited producer acceptance. Because sainfoin growth is poorest in the summer when the daylengths are longest, daylength influence on regrowth and persistence was investigated. Forty, 130‐d‐old (±4 d) ‘Renumex’ sainfoin plants were placed in growth chambers under daylengths of 10, 13, and 16 h of light daily. After a 14‐d adjustment period, plants were clipped to 2 cm. Clipped plants were allowed to regrow for 35 d (Harvest 1) clipped again and allowed to regrow for 14 additional days before final harvest (Harvest 2). Plant height, number of blooms, number of leaves, leaf area, and shoot dry mass were measured before each clipping and at final harvest (Harvest 2). Mass of taproots, fine roots and crowns as well as taproot reducing sugars, total sugars, and total nonstructural carbohydrate (TNC) were determined at Harvest 2. Activity of starch degrading enzymes and whole plant metabolism was measured at Harvest 2. Although daylength had some effects on sainfoin growth form (i.e., plant height and reproductive structures), the vegetative growth of sainfoin was otherwise unaltered by daylength (P > 0.05). Fine root mass was 38% (0.33 g plant−1) greater (P < 0.05) in the 16‐h treatment than in the 10‐h treatment. Taproot carbohydrates, starch enzyme activity, and metabolic heat rates were not altered by daylength (P > 0.05). Our results show that factors other than daylength regulate sainfoin growth after defoliation.