EFFECTS OF NITROGEN ON DEVELOPMENT AND GROWTH OF THE LEAVES OF VEGETABLES .3. APPEARANCE AND EXPANSION GROWTH OF LEAVES OF SPINACH

Leaf development in spinach (Spinacia oleracea L.) was studied in six field and glasshouse experiments. Treatments consisted of different am ounts and different ways of fractioning nitrogen supply. Rates of leaf appearance and leaf expansion were recorded, as well as final leaf si ze. The rate of leaf appearance varied between 0.16 and 0.57 d(-1) acr oss experiments, but was hardly affected by nitrogen treatment. The ra te of leaf expansion and the mature leaf area increased with leaf numb er, reached a maximum at leaf pair 3+4 or 5+6 and decreased subsequent ly. Both characteristics were positively correlated to nitrogen supply . The duration of expansion was not influenced by nitrogen treatments and varied between 15 and 30 days in most experiments. The rate of lea f expansion was the main factor determining mature leaf size. Specific leaf area over all green leaves slowly decreased with time in most ex periments and was around 300 cm(2) g(-1). As the differences in the nu mber of leaves were small, the differences in total green leaf area pe r plant resulted from differences in (mature) leaf area of individual leaves.