Tiller density and stand structure of tall fescue swards differing in age and nitrogen level

Abstract

Sward structure and tiller density are involved in the resistance of sown grasslands to the deterioration by ageing, and tiller density is known to be strongly affected by nitrogen. Tall fescue swards were sown in 1986 (old swards) and in 1990 (young swards) on the same site under an oceanic mountain climate. They were fertilised with 150 kg N ha −1 year −1 (N-poor swards) and with 350 kg N ha −1 year −1 (N-rich swards). All swards were cut simultaneously four times a year. In each sward type, the horizontal distribution of the tillers was mapped in ten quadrats, using grids of 10×15 square cells (2×2 cm), after each cut and throughout the growing seasons of 1992 and 1993. These growing seasons had reduced summer droughts after a dry year. The maps showed the heterogeneity of grass patches in a quadrat size (6 dm 2): areas without any tiller were adjacent to high-density areas (100 tillers dm −2 or more). The observed stand structures cannot be shown as a distribution of separate tufted plants. The high nitrogen level increased the mean tiller density, mainly by increasing the high density areas, and favoured the tiller aggregation. A 4-years ageing was equivalent to nitrogen starvation. The gap areas were poorly affected by the experimental treatments. They were reduced after 1 year of humid growing conditions. Ageing tall-fescue swards deteriorate through decreasing local competitiveness rather than through expanding openings.