Morphogenetic characteristics of timothy grown with varying N nutrition

The leaf area development of grasses and subsequently radiation interception depends on morphogenetic processes such as leaf extension and appearance. Leaf extension and appearance of timothy (Phleum pratense L.) grown with varying rates of N nutrition and their impact on sward structural characteristics were studied during primary growth in spring and during a summer regrowth. With no N applied in spring and summer, the leaf extension rate (LER) and the leaf appearance rate (LAR) of timothy were approximately 40% and 65% of that obtained under non-limiting N conditions (140 kg N ha(-1) in spring and 120 kg N ha(-1) in summer). Nitrogen deficiency reduced tiller density in spring but increased it in summer. The differential effect of the N deficiency on LER and LAR modified the sward structural characteristics. Nitrogen deficiency decreased the length of mature leaves, their width and the total leaf length per tiller. The reduced LER associated with N deficiency explained for the most part the N effect on leaf area expansion and radiation interception.