Relationship of tillering and morphological characteristics of two perennial ryegrass lines to “pulling” when grazed by dairy cows

Abstract

The morphology and sward structural characteristics of two perennial ryegrass pipeline (pre‐commercial) selections that showed different “pulling” tolerances, were studied at Hamilton, New Zealand. Pulling was defined as the removal of clumps of ryegrass plants from the sward during grazing. One line, coded as NZA1, was less tolerant of pulling than was the other, coded as NZA3. NZA3 is now commercially available as the cultivar ‘Bronsyn’. The ryegrass lines were established in small plots in May 1994 on a silt loam and a peaty silt loam soil. Half the area of each plot received nitrogen (N) fertiliser (30 kg N ha⁻¹) after each grazing, and tiller dynamics were monitored from September 1995 to April 1996. NZA1 had a higher leaf shear strength (6.21 versus 5.91 kg, standard error of difference (SED) = 0.087), wider leaves (3.621 versus 3.252 mm, SED = 0.0535), and a lower clump shear strength (13.4 versus 14.9 kg, SED = 0.57) than did NZA3. N fertiliser did not affect leaf shear strength, and tillering responses to N fertiliser were inconsistent. It is argued that better anchorage combined with leaves that break more easily when grazed contributed to less pulling of NZA3 than of NZA1 clumps during dry summers.

Keywords:

• ‘Bronsyn’ ryegrass
• Lolium perenne
• tiller dynamics
• leaf morphology
• leaf appearance rate
• leaf shear strength
• clump shear strength
• nitrogen fertiliser
• dairy cow grazing