Effect of spring defoliation pattern on the mid-season production and morphology of swards of perennial ryegrass cultivars of different maturity

The effect of three spring management treatments on the vertical distribution of dry-matter (DM) yield and morphology of four cultivars of perennial ryegrass (Fennema, Corbet, Foxtrot, Melle) in mid-season was investigated. The management treatments commenced with cuts on 15 February (Early), 1 March (Medium) and 29 March (Late), each followed by a 28-day re-growth period until the next cut and then further 21-day re-growth periods after each subsequent cut. This created four mid-season measurement periods across the management treatments at cut 3 (5 April-17 May), cut 5 (17 May-28 June), cut 6 (7 June-19 July) and cut 7 (28 June-9 August). Tiller and sheath height and their ratio, and leaf lamina length, were measured prior to the four mid-season cuts (cuts 3, 5, 6 and 7) when measurements of DM yield and proportions of leaf, stem and dead material in three herbage horizons (Lower, 0-8 cm; Middle, 8-15 cm; Upper, > 15 cm) were made. There were significant responses in mid-season to the management treatments involved complex interactions between management treatment and cutting date, which modified seasonal patterns in DM yield and leaf:stem ratio. There were significantly greater tiller heights, tiller:sheath ratios and leaf lamina lengths but lower sheath heights from the Early to Late management treatments. The greatest responses in morphological characteristics occurred in the Middle horizon compared with either the Lower (predominately stem and pseudo-stem), or the Upper (predominately leafy) horizons. Distribution of DM yield between Middle and Lower horizons but not overall DM yields was significantly affected by management treatment. Morphological differences between cultivars were mostly in the Middle horizon and ranking of the cultivars was similar across the management treatments. The different responses of cultivars Fennema and Melle showed that genotype had a significant effect regardless of management. The leafiest mid-season swards were achieved by delaying initial spring defoliation in the cultivar which had the lowest stem production.