Components of regrowth in grazed and cut Lolium perenne swards

Abstract

Growth measurements were made on Lolium /jerenoe-dominant vegetative swards during 4-week regrowth periods following grazing or cutting.In the grazing study, the ryegrass (Lolium perenne) swards were grazed for 12-d periods with stock numbers set according to initial herbage allowances per animal of 16, 32 and 64 kg organic matter per sheep. One area was grazed in summer and another area in the autumn.In the cutting experiment four ryegrass swards growing in boxes were prepared by cutting to either 2 or 6 cm at either 14-or 28-d intervals. The swards were cut back in autumn to 2 or 6 cm. During the regrowth period half the boxes were retained in full light and half shaded to 48% of incident light.Herbage weight, rates of leaf extension, senescence, leaf appearance and tillering, water soluble carbohydrate reserve levels in tiller bases and, in the cutting experiment, sheath tube lengths and lamina lengths of leaves which had grown through the sheath tube were measured at intervals during Ihe regrowth period.Final herbage weights reflected management history but net herbage accumulation over the four-week regrowth period, though affected by season, pretreatment and light level, was similar on swards subjected to different grazing or cutting treatments.This result was partially explained by changes in the balance between growth and senescence per tiller as herbage weight increased with time during regrowth. and partially by the reduced production per tiller in harder-grazed swards being offset by a rapid increase in tiller numbers.There was a positive curvilinear relationship between lamina length and the length of the sheath tubes through which the laminae emerged.Carbohydrate reserve levels declined rapidly after grazing or cutting, the extent of the decline being related to the severity of the defoliation. Recovery commenced after four days in summer and was complete within 3 weeks but reserve levels remained low in plants grazed or cut in autumn.The need is discussed for more detailed descriptions of sward states in management studies and for more infonnation on component processes of growth, the factors affecting them and how these interact with different kinds of management systems.

Using post-grazing sward height to impose dietary restrictions of varying duration in early lactation: its effects on spring-calving dairy cow production

“…However, there was no effect of treatment on sward DM production at any point during the experiment, which is perhaps attributable to the similarity in sward morphology, both above and below the grazing horizon, across treatments and the lack of difference in post-grazing HM >2.7 cm following P1. Furthermore, as swards were grazed at the target pre-grazing HM, there were similar proportions of leaf in both swards and it ensured that sufficient leaf remained post-grazing to intercept solar radiation, which is required for respiration and tissue growth (Grant et al, 1981). MacDonald et al (2008) found an increase in pasture quality as swards were defoliated to a lower PGSH, this is in contrast with the present experiment, which found no difference in sward quality.…”

Leaf and tiller growth ofLolium perenneandAgrostisspp. and leaf appearance rates ofTrifolium repensin set-stocked and rotationally grazed hill pastures

“…However, leaf production on an area basis is likely to be similar under both managements as leaf and tiller size and leaf extension rates were inversely related to tiller density. Similar effects have been reported by Grant et al (1981). Because such compensatory mechanisms operate in grazed swards, greater potential for improving pasture production in low fertility hill country would appear to lie in raising soil nutrient status than in changing grazing management practices, as shown by Lambert et al (1983).…”

Effects of postgrazing residue on morphogenetic and structural characteristics of Tifton 85 pastures

“…The FLL is a plastic characteristic of the plant that responds to grazing intensity imposed on pastures and it is considered a morphological plant strategy to be less affected in grazing (LEMAIRE; CHAPMAN, 1996). According to Grant et al (1981), the greater FLL values are associated with greater defoliation heights owing to the large sheath length, which is directly related to the SER. The leaf sheath size is greater at pastures kept higher than in pastures kept lower, which increases the distance that the leaf blade will travel from the apical meristem to the emergence, resulting in increased length of the expanded leaf.…”