Tillering and leaf area index in grasses in the vegetative phase

The relationship between tillering of a vegetative grass stand and Leaf Area Index (LAI) has been studied during sward establishment of perennial ryegrass and Italian ryegrass with different seedling densities and nitrogen fertilizer rates and on established swards of tall fescue during winter and early spring after different dates of last cut in autumn.
The different experiments on different species led to the conclusion that in every instance the tillering rate slows down as soon as the LAI reaches a value of 3 and terminates rapidly at higher LAI, which corresponds with the almost complete extinction of light at the level of the tiller buds. The results confirm the direct role of light on morphogenesis previously demonstrated by several authors. The existence of such a limit of LAI helps to explain some contradictory effects of temperature or nitrogen on tillering.