EFFECTS OF NITROGEN ON DEVELOPMENT AND GROWTH OF THE LEAVES OF VEGETABLES .2. APPEARANCE, EXPANSION GROWTH AND LIFE-SPAN OF LEAVES OF LEEK PLANTS

Leaf growth and development of leek (Allium porrum L.) were examined i n three experiments, with different amounts and dates of application o f nitrogen as treatments. Rates of leaf appearance, leaf expansion, le af size and leaf senescence were measured. The rate of leaf appearance was not affected by N treatments and almost constant across experimen ts at 0.15 d(-1). The rate of leaf expansion and the mature leaf area increased with leaf number, reached a maximum between leaf numbers 11 and 14 and decreased with higher leaf numbers. Both variables increase d with more nitrogen. The duration of leaf expansion was more or less constant across leaf numbers and not influenced by nitrogen treatments ; the leaf expansion rate was the main factor determining mature leaf area. The race of leaf senescence was not influenced by N treatments. Differences in total green leaf area per plant were caused by differen ces in (mature) leaf area of individual leaves and not by the differen ces in the number of leaves. The specific leaf area of all leaves was more or less constant at 100 cm(2) g(-1).