Effects of Nitrogen on the Development and Growth of the Potato Plant. 1. Leaf Appearance, Expansion Growth, Life Spans of Leaves and Stem Branching

Potatoes (Solanum tuberosum L) were planted in pots in a temperature-controlled glasshouse to collect data on the rate of leaf apearance, leaf expansion, apical lateral branching and active life spans of leaves The treatments consisted of three rates of nitrogen supply, i e the NI treatment with 2 5 g N per pot and the N2 and N3 treatments with 8 and 16 g N per pot, respectively The rate of leaf appearance was 0·53 leaves d−1 (one leaf per 28 °C d) and was negligibly affected by nitrogen supply The rate of leaf expansion was related to leaf number and nitrogen supply The areas of mature leaves increased with leaf number on the main stem to reach a maximum for leaf numbers 12–14, and declined for higher leaf numbers Leaves on apical lateral branches declined in mature area with increase in leaf number The expansion rate of leaves was the dominant factor that determined the mature leaf area, irrespective of leaf number and nitrogen treatment The smallest leaves were observed at the lowest rate of nitrogen supply Nitrogen promoted apical branching and hence the total number of leaves that appeared on a plant The proportion of total leaf area contributed by leaves on apical branches increased with time and nitrogen supply Active life span, i e the period of time between leaf appearance and yellowing of the leaf, showed a similar relation to leaf number as mature leaf area, at least in qualitative terms Leaves of the N3 treatment showed systematically longer life spans than leaves of the NI and N2 treatment in the order of 3 weeks The number of main stem leaves was not affected by nitrogen supply