Effects of applied nitrogen on grass leaf initiation, development and death in field swards

Publisher Website
Google Scholar
Abstract
SUMMARY: Effects of three levels of N application and four intervals between harvests on field swards of perennial ryegrass (Lolium perenne L.) were studied during 6-week periods in summer and spring. Ryegrass was compared with tall fescue (Festuca arundinacea Schreb.) in spring and autumn.The application of N increased the rate of production of leaf primordia, the number of leaf primordia per tiller, the length of the shoot apex, the rate of development of primordia into unemerged leaves, the number of leaves emerging, the number of live, emerged leaves per tiller, the leaf extension rate and weight of blade emerging and the net gain, per tiller per day, in blade length and weight. The application of N tended to reduce the number of unemerged leaves per tiller and the length of apex per primordium. Applied N retarded leaf death (whether measured as numbers, length or weight) during the first 2–3 weeks after application and accelerated death subsequently. During the 1st week of the summer periods, the net gain in green blade length and weight per tiller was doubled by 22 kg N/ha and trebled by 66 kg N (compared with nil). During the final fortnight of the summer periods, the net gain in green blade length and weight was less with the 6-than with the 3- or 2-week interval, and, in the case of the 6-week interval, the positive effect of applied N on the rate of development of primordia into unemerged leaves and on the number of leaves emerging had been lost.The ryegrass had more leaf primordia and unemerged leaves per tiller than the fescue, and a faster rate of development of primordia into unemerged leaves and of unemerged into emerged leaves.A ryegrass leaf spent a broadly similar length of time in each of the three stages, primordium, unemerged leaf and fully expanded live leaf, and about half as long as one of those stages as an emerging leaf. At nil N a leaf developed to about 6000 times its starting length (as a newly-formed primordium) in 67 days in summer; at high N a leaf developed to about 10500 times its starting length in 53 days. The percentage increase in length per day was greatest during the unemerged leaf stage.