Taproot and Adventitious Root Growth of White Clover as Influenced by Nitrogen Nutrition

White clover ( Trifolium repens L.) seedlings form a taproot that persists for only 1 to 2 yr under field conditions. Subsequent growth and persistence depend on adventitious roots formed at stolon nodes. Few studies have attempted to compare characters of taproot with those of adventitious root systems. The objectives of this study were to compare root characters of white clover genotypes grown with taproot and adventitious root systems, and to determine the effect of N source on these characters. A randomized complete block design in a 2 ✕ 3 factorial was used with two N levels (+N and −N Hoagland solution) and three white clover cultivars (‘Regal’, ‘Dusi’, and ‘Louisiana S‐1’) that were inoculated with Rhizobium trifolii . All plants were grown in Cone‐tainers (Ray Leach Cone‐tainer Nursery, Canby, OR) in the greenhouse for 10 wk, with seedlings used for the initial taproot evaluation and stolon tip cuttings used for the subsequent adventitious root evaluation. The + N plants had 55 to 283% and 62 to 208% greater root and shoot dry weights, respectively, than the −N plants. Regal had 10% greater adventitious root dry weights than Dusi, though Dusi was originally selected for large adventitious roots. Louisiana S‐1 averaged 15% smaller diameter roots, 16% fewer fibrous roots, 25% less root dry weight, and 14% more nodule mass than Regal and Dusi. Differences among cultivars for root diameter, secondary root number, fibrous root score, nodule mass, and root dry weight were similarly expressed in both taproot and adventitious root systems. Selection for more fibrous roots in a taproot system should lead to more fibrous roots in an adventitious root system.