The effect of interval between harvests and nitrogen application on initiation, emergence and longevity of leaves, longevity of tillers and dimensions and weights of leaves and ‘stems’ in Lolium

Abstract

SummaryThe effects of six intervals between harvests and three levels of N application on the initiation, emergence and longevity of leaves and longevity of tillers of Italian ryegrass and on dimensions and weights of leaves of four ryegrass varieties were studied in the first harvest year in field experiments. Dimensions and weights of leaves and ‘stems’ of the four varieties were recorded on three dates in the second harvest year.The number of leaf primordia on the shoot apex of young Italian ryegrass tillers was increased by N application and seemed to be increased by increasing the period of uninterrupted growth allowed to the parent tillers. The number of leaves which emerged on marked tillers during a 30-week period was approximately halved by increasing the interval between harvests from 3 to 10 weeks, but was not affected by N application. The number of leaves which died on marked tillers was at least doubled by increasing the interval between harvests from 3 to 5 weeks. The second and third leaves to emerge on a tiller had a longer potential life than the first leaf. Increasing the interval between harvests greatly increased the average age of the green leaves in the canopy at the time of harvest.Length and width, but not thickness, of fully expanded green leaf blades were increased by both N application and increased interval between harvests. The effect of applied N in increasing leaf size appeared to be an important reason for the positive effect of N on yield, particularly with the longer intervals. The effect of N in increasing the number of tillers and leaves was important with the shorter intervals. Applied N reduced dry weight per unit volume of plant tissue and increased ‘stem’ length and increased weight and volume of herbage per unit volume of canopy. The area of exposed surface of ‘stem’ seemed too large to be ignored when considering the photosynthetic capacity of the canopy, particularly with the longer intervals.